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doc/ZEO/ClientStorage.txt
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......@@ -23,7 +23,9 @@ ClientStorage
- a sequence of the previous two
If a sequence of addresses is specified, the client will use the
first server from the list that it can connect to.
first server from the list that it can connect to, subject to the
constraints imposed by the optional read_only and
read_only_fallback keyword arguments.
The ClientStorage constructor provides a number of additional
options (arguments). The full list of arguments is:
......@@ -36,7 +38,7 @@ ClientStorage
default name for both the server and client is '1'.
cache_size -- The number of bytes to allow for the client cache.
The default is 20,000,000. A large cache can significantly
The default is 20MB. A large cache can significantly
increase the performance of a ZEO system. For applications that
have a large database, the default size may be too small.
......@@ -93,3 +95,8 @@ ClientStorage
Each storage served by a ZEO server can be configured as either
read-write or read-only.
read_only_fallback -- A flag indicating whether a read-only
remote storage should be acceptable as a fallback when no
writable storages are available. Defaults to false. At most
one of read_only and read_only_fallback should be true.
doc/ZEO/NonZopeREADME.txt
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......@@ -20,7 +20,7 @@ Zope Enterprize Objects
python test.py -v
Run the script with the -h option for a full list of options. The
ZEO 2.0a1 release contains 87 unit tests on Unix.
ZEO 2.0b2 release contains 122 unit tests on Unix.
Starting (and configuring) the ZEO Server
......@@ -75,6 +75,6 @@ Zope Enterprize Objects
Dependencies on other modules
ZEO depends on other modules that are distributed with
StandaloneZODB and with Zope. You can download StandaloneZODB
from http://www.zope.org/Products/StandaloneZODB.
ZEO depends on other modules that are distributed with ZODB3 and
with Zope. You can download ZODB3 from
http://www.zope.org/Products/StandaloneZODB.
doc/ZEO/ZopeREADME.txt
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Zope Enterprise Objects
Zope Enterprise Objects (ZEO)
Installation
......@@ -19,7 +19,7 @@ Zope Enterprise Objects
python test.py -v
Run the script with the -h option for a full list of options. The
ZEO 2.0a1 release contains 87 unit tests on Unix.
ZEO 2.0b2 release contains 122 unit tests on Unix.
Starting (and configuring) the ZEO Server
......@@ -93,4 +93,4 @@ Zope Enterprise Objects
once with the environment variable FORCE_PRODUCT_LOAD set.
The interaction between ZEO and Zope product installation is
unfortunate. In the future, this interaction will be removed by
unfortunate.
doc/guide/TODO
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Update text to use BTrees, not BTree
Write section on __setstate__
Connection.sync seems to work now; note this
Continue working on it
Suppress the full GFDL text in the PDF/PS versions
doc/guide/links.tex
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......@@ -17,6 +17,14 @@ how it's actually implemented. A definitive reference, and highly recommended.
\\
\url{http://www.python.org/workshops/2000-01/proceedings/papers/fulton/zodb3.html}
Persistent Programing with ZODB, by Jeremy Hylton and Barry Warsaw:
\\
Slides for a tutorial presented at the 10th Python conference. Covers
much of the same ground as this guide, with more details in some areas
and less in others.
\\
\url{http://www.zope.org/Members/bwarsaw/ipc10-slides}
Download link for ZEO: \\
\url{http://www.zope.org/Products/ZEO/}
......
doc/guide/modules.tex
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......@@ -2,13 +2,12 @@
% Related Modules
% PersistentMapping
% PersistentList
% BTree
% Catalog
% BTrees
\section{Related Modules}
The ZODB package includes a number of related modules that provide
useful data types such as BTrees or full-text indexes.
useful data types such as BTrees.
\subsection{\module{ZODB.PersistentMapping}}
......@@ -40,51 +39,92 @@ value for \var{initlist}, a regular Python list is used.
Python lists do.
\subsection{B-tree Modules}
%here's one: how does one implement searching? i would have expected the
%btree objects to have ``find key nearest to this'' and ``next'' methods,
%(like bsddb's set_location)...
%
% -- erno
\subsection{BTrees Package}
When programming with the ZODB, Python dictionaries aren't always what
you need. The most important case is where you want to store a very
large mapping. When a Python dictionary is accessed in a ZODB, the
whole dictionary has to be unpickled and brought into memory. If
you're storing something very large, such as a 100,000-entry user
database, unpickling such a large object will be slow. B-trees are a
database, unpickling such a large object will be slow. BTrees are a
balanced tree data structure that behave like a mapping but distribute
keys throughout a number of tree nodes. Nodes are then only unpickled
and brought into memory as they're accessed, so the entire tree
doesn't have to occupy memory (unless you really are touching every
single key).
There are four different BTree modules provided. One of them, the
\module{BTree} module, provides the most general data type; the keys
and values in the B-tree can be any Python object. Some specialized B-tree
modules require that the keys, and perhaps even the values, to be of a
certain type, and provide faster performance because of this limitation.
\begin{itemize}
\item[ \module{IOBTree} ] requires the keys to be integers.
The module name reminds you of this; the \module{IOBTree} module
maps Integers to Objects.
\item[ \module{OIBTree} ] requires the values to be integers,
mapping Objects to Integers.
\item[ \module{IIBTree} ] is strictest, requiring that both keys and values must be integers.
\end{itemize}
To use a B-tree, simply import the desired module and call the
constructor, always named \function{BTree()}, to get a B-tree
instance, and then use it like any other mapping:
keys throughout a number of tree nodes. The nodes are stored in
sorted order. Nodes are then only unpickled and brought into memory
as they're accessed, so the entire tree doesn't have to occupy memory
(unless you really are touching every single key).
The BTrees package provides a large collection of related data
structures. There are variants of the data structures specialized to
handle integer values, which are faster and use less memory. There
are four modules that handle the different variants. The first two
letters of the module name specify the types of the keys and values in
mappings -- O for any object and I for integer. The
\module{BTrees.IOBTree} module provides a mapping that accepts integer
keys and arbitrary objects as values.
The four data structures provide by each module are a btree, a bucket,
a tree set, and a set. The btree and bucket types are mappings and
support all the usual mapping methods, e.g. \function{update()} and
\function{keys()}. The tree set and set types are similar to mappings
but they have no values; they support the methods that make sense for
a mapping with no keys, e.g. \function{keys()} but not
\function{items()}. The bucket and set types are the individual
building blocks for btrees and tree sets, respectively. A bucket or
set can be used when you are sure that it will have few elements. If
the data structure will grow large, you should use a btree or tree
set.
The four modules are named \module{OOBTree}, \module{IOBTree},
\module{OIBTree}, and \module{IIBTree}. The two letter prefixes are
repeated in the data types names. The \module{BTrees.OOBTree} module
defines the following types: \class{OOBTree}, \class{OOBucket},
\class{OOSet}, and \class{OOTreeSet}.
The \function{keys()}, \function{values()}, and \function{items()}
methods do not materialize a list with all of the data. Instead, they
return lazy sequences that fetch data from the BTree as needed. They
also support optional arguments to specify the minium and maximum
values to return.
A BTree object supports all the methods you would expect of a mapping
with a few extensions that exploit the fact that the keys are sorted.
The example below demonstrates how some of the methods work. The
extra methods re \function{minKey()} and \function{maxKey()}, which
find the minimum and maximum key value subject to an optional bound
argument, and \function{byValue()}, which returns value, key pairs
in reversed sorted order subject to an optional minimum bound argument.
\begin{verbatim}
import IIBTree
iimap = IIBTree.BTree()
iimap[1972] = 27
>>> from BTrees.OOBTree import OOBTree
>>> t = OOBTree()
>>> t.update({ 1: "red", 2: "green", 3: "blue", 4: "spades" })
>>> len(t)
4
>>> t[2]
'green'
>>> t.keys()
<OOBTreeItems object at 0x40269098>
>>> [k for k in t.keys()] # use a listcomp to get a printable sequence
[1, 2, 3, 4]
>>> [k for k in t.values()]
['red', 'green', 'blue', 'spades']
>>> [k for k in t.values(1, 2)]
['red', 'green']
>>> [k for k in t.values(2)]
['green', 'blue', 'spades']
>>> t.byValue("glue") # all values > "glue"
[('spades', 4), ('red', 1), ('green', 2)]
>>> t.minKey(1.5)
2
\end{verbatim}
Each of the modules also defines some functions that operate on
BTrees -- \function{difference()}, \function{union()}, and
\function{difference()}. The \function{difference()} function returns
a bucket, while the other two methods return a set.
If the keys are integers, then the module also defines
\function{multiunion()}. If the values are integers, then the module
also defines \function{weightedIntersection()} and
\function{weighterUnion()}. The function doc strings describe each
function briefly.
doc/guide/prog-zodb.tex
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doc/guide/transactions.tex
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......@@ -35,7 +35,7 @@ or \method{abort()} method of the \class{Transaction} object.
\begin{verbatim}
# Commit a subtransaction
get_transaction().commit(1)
get_transaction().commit(1)
# Abort a subtransaction
get_transaction().abort(1)
......@@ -103,6 +103,16 @@ transaction''. Usually this will happen because later transactions
modified the objects affected by the transaction you're trying to
undo.
After you call \method{undo()} you must commit the transaction for the
undo to actually be applied.
\footnote{There are actually two different ways a storage can
implement the undo feature. Most of the storages that ship with ZODB
use the transactional form of undo described in the main text. Some
storages may use a non-transactional undo makes changes visible
immediately.} There is one glitch in the undo process. The thread
that calls undo may not see the changes to the object until it calls
\method{Connection.sync()} or commits another transaction.
\subsection{Versions}
While many subtransactions can be contained within a single regular
......@@ -161,6 +171,3 @@ The \class{Storage} and \class{DB} instances can be shared among
several threads, as long as individual \class{Connection} instances
are created for each thread.
XXX I can't think of anything else to say about multithreaded ZODB
programs. Suggestions? An example program?
doc/guide/zeo.tex
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......@@ -18,22 +18,21 @@ them in a distributed fashion without Zope ever entering the picture.
The combination of ZEO and ZODB is essentially a Python-specific
object database.
ZEO consists of about 1400 lines of Python code. The code is
relatively small because it contains only code for a TCP/IP server,
and for a new type of Storage, \class{ClientStorage}.
\class{ClientStorage} doesn't use disk files at all; it simply
makes remote procedure calls to the server, which then passes them on
a regular \class{Storage} class such as \class{FileStorage}. The
following diagram lays out the system:
ZEO consists of about 6000 lines of Python code, excluding tests. The
code is relatively small because it contains only code for a TCP/IP
server, and for a new type of Storage, \class{ClientStorage}.
\class{ClientStorage} simply makes remote procedure calls to the
server, which then passes them on a regular \class{Storage} class such
as \class{FileStorage}. The following diagram lays out the system:
XXX insert diagram here later
Any number of processes can create a \class{ClientStorage}
instance, and any number of threads in each process can be using that
instance. \class{ClientStorage} aggressively caches objects
locally, so in order to avoid using stale data, the ZEO server sends
an invalidate message to all the connected \class{ClientStorage}
instances on every write operation. The invalidate message contains
locally, so in order to avoid using stale data. The ZEO server sends
an invalidation message to all the connected \class{ClientStorage}
instances on every write operation. The invalidation message contains
the object ID for each object that's been modified, letting the
\class{ClientStorage} instances delete the old data for the
given object from their caches.
......@@ -46,7 +45,9 @@ writes, and ZEO is therefore better suited for read-intensive
applications. If every \class{ClientStorage} is writing to the
database all the time, this will result in a storm of invalidate
messages being sent, and this might take up more processing time than
the actual database operations themselves.
the actual database operations themselves.\footnote{These messages are
small and sent in batches, so there would need to be a lot of writes
before it became a problem.}
On the other hand, for applications that have few writes in comparison
to the number of read accesses, this aggressive caching can be a major
......@@ -69,36 +70,17 @@ configure and run a ZEO Storage Server on a machine.
\subsubsection{Requirements}
To run a ZEO server, you'll need Python 1.5.2 or 2.0, and the ZODB
packages from \url{http://www.amk.ca/files/zodb/}
have to be installed.
\emph{Note for Python 1.5.2 users}: ZEO requires updated versions
of the \module{asyncore.py} and \module{asynchat.py} modules that are
included in 1.5.2's standard library. Current versions of the ZODB
distribution install private versions of these modules, so you
shouldn't need to grab updated versions yourself. (The symptom of
this problem is a traceback on attempting to run a ZEO client program:
the traceback is ``TypeError: too many arguments; expected 2, got 3''
around line 100 of \file{smac.py}.
\subsubsection{Installation}
Installing the ZEO package is easy. Just run \code{python setup.py
install}. This will install the ZEO/ package into your Python
installation, and copy various files into their proper locations:
\file{zeo.conf} will be put into \file{/usr/local/etc/}, a \file{zeo} startup
script will be put in \file{/etc/rc.d/init.d/}, and the \file{zeod}
daemon program will be placed in \file{/usr/local/bin}.
\subsection{Configuring and Running a ZEO Server}
Edit \code{/usr/local/etc/zeo.conf} appropriately for your desired
setup. This configuration file controls the port on which ZEO will
listen for connections, the user and group IDs under which the server
will be executed, and the location of the concrete \class{Storage}
object that will be made network-accessible.
The ZEO server software is included in ZODB3. As with the rest of
ZODB3, you'll need Python 2.1 or higher.
\subsubsection{Running a server}
The start.py script in the ZEO directory can be used to start a
server. Run it with the -h option to see the various values. If
you're just experimenting, a good choise is to use
\code{python ZEO/start.py -D -U /tmp/zeosocket} to run ZEO in
debug mode and with a Unix domain socket.
\subsection{Testing the ZEO Installation}
Once a ZEO server is up and running, using it is just like using ZODB
......@@ -137,15 +119,15 @@ If this code runs properly, then your ZEO server is working correctly.
\subsection{ZEO Programming Notes}
XXX The Connection.sync() method and its necessity (if it works at all!)
% That doesn't work. I tested it. sync() doesn't seem to get into
% the asyncore loop. One of us should probably look into adding an
% API for this when we have some free time. It would be a nice
% small project that would get into ZODB's guts.
ZEO is written using \module{asyncore}, from the Python standard
library. It assumes that some part of the user application is running
an \module{asyncore} mainloop. For example, Zope run the loop in a
separate thread and ZEO uses that. If your application does not have
a mainloop, ZEO will not process incoming invalidation messages until
you make some call into ZEO. The \method{Connection.sync} method can
be used to process pending invalidation messages. You can call it
when you want to make sure the \class{Connection} has the most recent
version of every object, but you don't have any other work for ZEO to do.
\subsection{Sample Application: chatter.py}
......@@ -174,7 +156,7 @@ class ChatSession(Persistent):
def __init__(self, name):
self.name = name
# Internal attribute: _messages holds all the chat messages.
self._messages = BTree.BTree()
self._messages = BTrees.OOBTree.OOBTree()
\end{verbatim}
\method{add_message()} has to add a message to the
......
doc/guide/zodb.dvi
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doc/guide/zodb.tex
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\documentclass{howto}
\title{ZODB/ZEO Programming Guide}
\release{0.03}
\release{0.04}
\date{\today}
\author{A.M.\ Kuchling}
......
doc/guide/zodb/about.html
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......@@ -6,19 +6,20 @@
<META NAME="keywords" CONTENT="zodb">
<META NAME="resource-type" CONTENT="document">
<META NAME="distribution" CONTENT="global">
<meta http-equiv="Content-Type" content="text/html; charset=">
<link rel="STYLESHEET" href="zodb.css">
<meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1">
<link rel="STYLESHEET" href="zodb.css" type='text/css'>
<link rel="first" href="zodb.html">
<link rel="contents" href="contents.html" title="Contents">
<LINK REL="previous" HREF="node41.html">
<LINK REL="previous" HREF="node39.html">
<LINK REL="up" HREF="zodb.html">
<meta name='aesop' content='information'>
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<body>
<DIV CLASS="navigation">
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border="0" height="32"
alt="Previous Page" width="32"></A></td>
<td><A HREF="zodb.html"><img src="/python/writing/icons/up.gif"
......@@ -38,7 +39,7 @@
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alt="" width="32"></td>
</tr></table>
<b class="navlabel">Previous:</b> <a class="sectref" HREF="node53.html">ADDENDUM: How to use</A>
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<b class="navlabel">Up:</b> <a class="sectref" HREF="zodb.html">ZODB/ZEO Programming Guide</A>
<br><hr>
</DIV>
......@@ -48,7 +49,7 @@
About this document ...</A>
</H1>
<strong>ZODB/ZEO Programming Guide</strong>,
February 8, 2002, Release 0.03
October 4, 2002, Release 0.04
<p> This document was generated using the <a
href="http://saftsack.fs.uni-bayreuth.de/~latex2ht/">
<strong>LaTeX</strong>2<tt>HTML</tt></a> translator.
......@@ -78,7 +79,7 @@ February 8, 2002, Release 0.03
<p><hr>
<table align="center" width="100%" cellpadding="0" cellspacing="2">
<tr>
<td><A HREF="node53.html"><img src="/python/writing/icons/previous.gif"
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border="0" height="32"
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......@@ -98,10 +99,10 @@ February 8, 2002, Release 0.03
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alt="" width="32"></td>
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<b class="navlabel">Previous:</b> <a class="sectref" HREF="node53.html">ADDENDUM: How to use</A>
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<b class="navlabel">Up:</b> <a class="sectref" HREF="zodb.html">ZODB/ZEO Programming Guide</A>
<hr>
<span class="release-info">Release 0.03, documentation updated on February 8, 2002.</span>
<span class="release-info">Release 0.04, documentation updated on October 4, 2002.</span>
</DIV>
<!--End of Navigation Panel-->
......
doc/guide/zodb/contents.html
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......@@ -6,8 +6,8 @@
<META NAME="keywords" CONTENT="zodb">
<META NAME="resource-type" CONTENT="document">
<META NAME="distribution" CONTENT="global">
<meta http-equiv="Content-Type" content="text/html; charset=">
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<link rel="STYLESHEET" href="zodb.css" type='text/css'>
<link rel="first" href="zodb.html">
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......@@ -15,6 +15,7 @@
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<LINK REL="up" HREF="zodb.html">
<LINK REL="next" HREF="node2.html">
<meta name='aesop' content='information'>
</head>
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<DIV CLASS="navigation">
......@@ -66,45 +67,44 @@ Contents</A>
<LI><A href="node13.html">2.3 Opening a ZODB</a>
<LI><A href="node14.html">2.4 Writing a Persistent Class</a>
<LI><A href="node15.html">2.5 Rules for Writing Persistent Classes</a>
<LI><A href="node20.html">2.6 Writing Persistent Classes</a>
<LI><A href="node19.html">2.6 Writing Persistent Classes</a>
</ul>
<LI><A href="zeo.html">3 ZEO</a>
<UL>
<LI><A href="node23.html">3.1 How ZEO Works</a>
<LI><A href="node24.html">3.2 Installing ZEO</a>
<LI><A href="node27.html">3.3 Configuring and Running a ZEO Server</a>
<LI><A href="node28.html">3.4 Testing the ZEO Installation</a>
<LI><A href="node29.html">3.5 ZEO Programming Notes</a>
<LI><A href="node30.html">3.6 Sample Application: chatter.py</a>
<LI><A href="node22.html">3.1 How ZEO Works</a>
<LI><A href="node23.html">3.2 Installing ZEO</a>
<LI><A href="node26.html">3.3 Testing the ZEO Installation</a>
<LI><A href="node27.html">3.4 ZEO Programming Notes</a>
<LI><A href="node28.html">3.5 Sample Application: chatter.py</a>
</ul>
<LI><A href="node31.html">4 Transactions and Versioning</a>
<LI><A href="node29.html">4 Transactions and Versioning</a>
<UL>
<LI><A href="node32.html">4.1 Subtransactions</a>
<LI><A href="node33.html">4.2 Undoing Changes</a>
<LI><A href="node34.html">4.3 Versions</a>
<LI><A href="node35.html">4.4 Multithreaded ZODB Programs</a>
<LI><A href="node30.html">4.1 Subtransactions</a>
<LI><A href="node31.html">4.2 Undoing Changes</a>
<LI><A href="node32.html">4.3 Versions</a>
<LI><A href="node33.html">4.4 Multithreaded ZODB Programs</a>
</ul>
<LI><A href="node36.html">5 Related Modules</a>
<LI><A href="node34.html">5 Related Modules</a>
<UL>
<LI><A href="node37.html">5.1 <tt class="module">ZODB.PersistentMapping</tt></a>
<LI><A href="node38.html">5.2 <tt class="module">ZODB.PersistentList</tt></a>
<LI><A href="node39.html">5.3 B-tree Modules</a>
<LI><A href="node35.html">5.1 <tt class="module">ZODB.PersistentMapping</tt></a>
<LI><A href="node36.html">5.2 <tt class="module">ZODB.PersistentList</tt></a>
<LI><A href="node37.html">5.3 BTrees Package</a>
</ul>
<LI><A href="node40.html">A. Resources</a>
<LI><A href="node41.html">B. GNU Free Documentation License</a>
<LI><A href="node38.html">A. Resources</a>
<LI><A href="node39.html">B. GNU Free Documentation License</a>
<UL>
<LI><A href="node42.html">Preamble</a>
<LI><A href="node43.html">B..1 Applicability and Definitions</a>
<LI><A href="node44.html">B..2 Verbatim Copying</a>
<LI><A href="node45.html">B..3 Copying in Quantity</a>
<LI><A href="node46.html">B..4 Modifications</a>
<LI><A href="node47.html">B..5 Combining Documents</a>
<LI><A href="node48.html">B..6 Collections of Documents</a>
<LI><A href="node49.html">B..7 Aggregation With Independent Works</a>
<LI><A href="node50.html">B..8 Translation</a>
<LI><A href="node51.html">B..9 Termination</a>
<LI><A href="node52.html">B..10 Future Revisions of This Licence</a>
<LI><A href="node53.html">ADDENDUM: How to use this License for your documents</a>
<LI><A href="node40.html">Preamble</a>
<LI><A href="node41.html">B..1 Applicability and Definitions</a>
<LI><A href="node42.html">B..2 Verbatim Copying</a>
<LI><A href="node43.html">B..3 Copying in Quantity</a>
<LI><A href="node44.html">B..4 Modifications</a>
<LI><A href="node45.html">B..5 Combining Documents</a>
<LI><A href="node46.html">B..6 Collections of Documents</a>
<LI><A href="node47.html">B..7 Aggregation With Independent Works</a>
<LI><A href="node48.html">B..8 Translation</a>
<LI><A href="node49.html">B..9 Termination</a>
<LI><A href="node50.html">B..10 Future Revisions of This Licence</a>
<LI><A href="node51.html">ADDENDUM: How to use this License for your documents</a>
</ul>
<LI><A href="about.html">About this document ...</a>
</ul>
......@@ -147,7 +147,7 @@ Contents</A>
<b class="navlabel">Up:</b> <a class="sectref" HREF="zodb.html">ZODB/ZEO Programming Guide</A>
<b class="navlabel">Next:</b> <a class="sectref" HREF="node2.html">1 Introduction</A>
<hr>
<span class="release-info">Release 0.03, documentation updated on February 8, 2002.</span>
<span class="release-info">Release 0.04, documentation updated on October 4, 2002.</span>
</DIV>
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\title{ZODB/ZEO Programming Guide}
\release{0.03}
\release{0.04}
\date{\today}
\author{A.M.\ Kuchling}\authoraddress{akuchlin@mems-exchange.org}
......@@ -150,7 +150,6 @@
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{\newpage\clearpage
\lthtmlinlinemathA{tex2html_wrap_inline847}%
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$\copyright$%
\lthtmlinlinemathZ
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<META NAME="keywords" CONTENT="zodb">
<META NAME="resource-type" CONTENT="document">
<META NAME="distribution" CONTENT="global">
<meta http-equiv="Content-Type" content="text/html; charset=">
<link rel="STYLESHEET" href="zodb.css">
<meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1">
<link rel="STYLESHEET" href="zodb.css" type='text/css'>
<link rel="first" href="zodb.html">
<link rel="contents" href="contents.html" title="Contents">
<LINK REL="next" href="contents.html">
<meta name='aesop' content='information'>
</head>
<body>
<DIV CLASS="navigation">
......@@ -47,8 +48,8 @@
<h1>ZODB/ZEO Programming Guide</h1>
<p><b><font size="+2">A.M. Kuchling</font></b></p>
<p>akuchlin@mems-exchange.org</p>
<p><strong>Release 0.03</strong><br>
<strong>February 8, 2002</strong></p>
<p><strong>Release 0.04</strong><br>
<strong>October 4, 2002</strong></p>
<p>
</center>
</div>
......@@ -81,55 +82,53 @@
<UL>
<LI><A href="node16.html">2.5.1 Modifying Mutable Objects</a>
<LI><A href="node17.html">2.5.2 Some Special Methods Don't Work</a>
<LI><A href="node18.html">2.5.3 Fixing <tt class="function">isinstance</tt> and <tt class="function">issubclass</tt></a>
<LI><A href="node19.html">2.5.4 <tt class="method">__getattr__</tt>, <tt class="method">__delattr__</tt>, and <tt class="method">__setattr__</tt></a>
<LI><A href="node18.html">2.5.3 <tt class="method">__getattr__</tt>, <tt class="method">__delattr__</tt>, and <tt class="method">__setattr__</tt></a>
</ul>
<LI><A href="node20.html">2.6 Writing Persistent Classes</a>
<LI><A href="node19.html">2.6 Writing Persistent Classes</a>
<UL>
<LI><A href="node21.html">2.6.1 Changing Instance Attributes</a>
<LI><A href="node20.html">2.6.1 Changing Instance Attributes</a>
</ul>
</ul>
<LI><A href="zeo.html">3 ZEO</a>
<UL>
<LI><A href="node23.html">3.1 How ZEO Works</a>
<LI><A href="node24.html">3.2 Installing ZEO</a>
<LI><A href="node22.html">3.1 How ZEO Works</a>
<LI><A href="node23.html">3.2 Installing ZEO</a>
<UL>
<LI><A href="node25.html">3.2.1 Requirements</a>
<LI><A href="node26.html">3.2.2 Installation</a>
<LI><A href="node24.html">3.2.1 Requirements</a>
<LI><A href="node25.html">3.2.2 Running a server</a>
</ul>
<LI><A href="node27.html">3.3 Configuring and Running a ZEO Server</a>
<LI><A href="node28.html">3.4 Testing the ZEO Installation</a>
<LI><A href="node29.html">3.5 ZEO Programming Notes</a>
<LI><A href="node30.html">3.6 Sample Application: chatter.py</a>
<LI><A href="node26.html">3.3 Testing the ZEO Installation</a>
<LI><A href="node27.html">3.4 ZEO Programming Notes</a>
<LI><A href="node28.html">3.5 Sample Application: chatter.py</a>
</ul>
<LI><A href="node31.html">4 Transactions and Versioning</a>
<LI><A href="node29.html">4 Transactions and Versioning</a>
<UL>
<LI><A href="node32.html">4.1 Subtransactions</a>
<LI><A href="node33.html">4.2 Undoing Changes</a>
<LI><A href="node34.html">4.3 Versions</a>
<LI><A href="node35.html">4.4 Multithreaded ZODB Programs</a>
<LI><A href="node30.html">4.1 Subtransactions</a>
<LI><A href="node31.html">4.2 Undoing Changes</a>
<LI><A href="node32.html">4.3 Versions</a>
<LI><A href="node33.html">4.4 Multithreaded ZODB Programs</a>
</ul>
<LI><A href="node36.html">5 Related Modules</a>
<LI><A href="node34.html">5 Related Modules</a>
<UL>
<LI><A href="node37.html">5.1 <tt class="module">ZODB.PersistentMapping</tt></a>
<LI><A href="node38.html">5.2 <tt class="module">ZODB.PersistentList</tt></a>
<LI><A href="node39.html">5.3 B-tree Modules</a>
<LI><A href="node35.html">5.1 <tt class="module">ZODB.PersistentMapping</tt></a>
<LI><A href="node36.html">5.2 <tt class="module">ZODB.PersistentList</tt></a>
<LI><A href="node37.html">5.3 BTrees Package</a>
</ul>
<LI><A href="node40.html">A. Resources</a>
<LI><A href="node41.html">B. GNU Free Documentation License</a>
<LI><A href="node38.html">A. Resources</a>
<LI><A href="node39.html">B. GNU Free Documentation License</a>
<UL>
<LI><A href="node42.html">Preamble</a>
<LI><A href="node43.html">B..1 Applicability and Definitions</a>
<LI><A href="node44.html">B..2 Verbatim Copying</a>
<LI><A href="node45.html">B..3 Copying in Quantity</a>
<LI><A href="node46.html">B..4 Modifications</a>
<LI><A href="node47.html">B..5 Combining Documents</a>
<LI><A href="node48.html">B..6 Collections of Documents</a>
<LI><A href="node49.html">B..7 Aggregation With Independent Works</a>
<LI><A href="node50.html">B..8 Translation</a>
<LI><A href="node51.html">B..9 Termination</a>
<LI><A href="node52.html">B..10 Future Revisions of This Licence</a>
<LI><A href="node53.html">ADDENDUM: How to use this License for your documents</a>
<LI><A href="node40.html">Preamble</a>
<LI><A href="node41.html">B..1 Applicability and Definitions</a>
<LI><A href="node42.html">B..2 Verbatim Copying</a>
<LI><A href="node43.html">B..3 Copying in Quantity</a>
<LI><A href="node44.html">B..4 Modifications</a>
<LI><A href="node45.html">B..5 Combining Documents</a>
<LI><A href="node46.html">B..6 Collections of Documents</a>
<LI><A href="node47.html">B..7 Aggregation With Independent Works</a>
<LI><A href="node48.html">B..8 Translation</a>
<LI><A href="node49.html">B..9 Termination</a>
<LI><A href="node50.html">B..10 Future Revisions of This Licence</a>
<LI><A href="node51.html">ADDENDUM: How to use this License for your documents</a>
</ul>
<LI><A href="about.html">About this document ...</a>
</ul>
......@@ -161,7 +160,7 @@
</tr></table>
<b class="navlabel">Next:</b> <a class="sectref" href="contents.html">Contents</A>
<hr>
<span class="release-info">Release 0.03, documentation updated on February 8, 2002.</span>
<span class="release-info">Release 0.04, documentation updated on October 4, 2002.</span>
</DIV>
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<META NAME="distribution" CONTENT="global">
<meta http-equiv="Content-Type" content="text/html; charset=">
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<meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1">
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......@@ -52,36 +53,15 @@
</H3>
<P>
You'll need Python, of course; version 1.5.2 works with some fixes,
and it also works with Python 2.0, which is what I primarily use.
<P>
The code is packaged using Distutils, the new distribution tools for
Python introduced in Python 2.0. If you're using 1.5.2, first you'll
have to get the latest Distutils release from the Distutils SIG page
at <a class="url" href="http://www.python.org/sigs/distutils-sig/download.html">http://www.python.org/sigs/distutils-sig/download.html</a> and
install it. This is simply a matter of untarring or unzipping the
You will need Python 2.1 or higher. The code is packaged using
Distutils. So it is simply a matter of untarring or unzipping the
release package, and then running <code>python setup.py install</code>.
<P>
If you're using 1.5.2 and have installed previous versions of the
Distutils, be sure to get the very latest version, since developing
the ZODB distribution turned up some bugs along the way. If you
encounter problems compiling <span class="file">ZODB/TimeStamp.c</span> or your compiler reports
an error like ``Can't create build/temp.linux2/ExtensionClass.o: No
such file or directory'', you need an updated version. Old versions of
Distutils have two bugs which affect the setup scripts. First, for a
long time the <code>define_macros</code> keyword in setup.py files didn't work due
to a Distutils bug, so I hacked TimeStamp.c in earlier releases. The
Distutils have since been fixed, and the hack became unnecessary, so I
removed it. Second, the code that creates directories tries to be
smart and caches them to save time by not trying to create a directory
twice, but this code was broken in old versions.
<P>
You'll need a C compiler to build the packages, because there are
various C extension modules. At the moment no one is making Windows
binaries available, so you'll need a Windows development environment to use the
binaries available, so you'll need a Windows development environment
to build ZODB.
<P>
......@@ -113,7 +93,7 @@ binaries available, so you'll need a Windows development environment to use the
<b class="navlabel">Up:</b> <a class="sectref" HREF="node9.html">2.1 Installing ZODB</A>
<b class="navlabel">Next:</b> <a class="sectref" HREF="node11.html">2.1.2 Installing the Packages</A>
<hr>
<span class="release-info">Release 0.03, documentation updated on February 8, 2002.</span>
<span class="release-info">Release 0.04, documentation updated on October 4, 2002.</span>
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<META NAME="keywords" CONTENT="zodb">
<META NAME="resource-type" CONTENT="document">
<META NAME="distribution" CONTENT="global">
<meta http-equiv="Content-Type" content="text/html; charset=">
<link rel="STYLESHEET" href="zodb.css">
<meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1">
<link rel="STYLESHEET" href="zodb.css" type='text/css'>
<link rel="first" href="zodb.html">
<link rel="contents" href="contents.html" title="Contents">
<LINK REL="previous" HREF="node10.html">
<LINK REL="up" HREF="node9.html">
<LINK REL="next" HREF="node12.html">
<meta name='aesop' content='information'>
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......@@ -52,38 +53,9 @@
<P>
Download the ZODB tarball containing all the packages for both ZODB
and ZEO from <a class="url" href="http://www.amk.ca/files/zodb/">http://www.amk.ca/files/zodb/</a>.
<P>
To build the packages, you must go into the individual directories and
build and install them one by one. They should be built and installed
in this order:
<P>
<OL>
<LI><code>zodb-basic</code>
</LI>
<LI>ExtensionClass
</LI>
<LI>ZODB
</LI>
<LI><code>BTree</code> and <code>BTrees</code>
</LI>
<LI>ZEO
</LI>
</OL>
<P>
In particular, you must install ExtensionClass before building the
ZODB package; otherwise, the compilation in the ZODB package will die
complaining that it can't find ExtensionClass.h. You can manually
hack the #include path to make it work without installing
ExtensionClass first, but that's a bit hackish.
<P>
If you encounter any problems, please let me know at
<span class="email">akuchlin@mems-exchange.org</span>.
and ZEO from <a class="url" href="http://www.zope.org/Products/StandaloneZODB">http://www.zope.org/Products/StandaloneZODB</a>. See
the <span class="file">README.txt</span> file in the top level of the release directory
for details on building, testing, and installing.
<P>
......@@ -115,7 +87,7 @@ If you encounter any problems, please let me know at
<b class="navlabel">Up:</b> <a class="sectref" HREF="node9.html">2.1 Installing ZODB</A>
<b class="navlabel">Next:</b> <a class="sectref" HREF="node12.html">2.2 How ZODB Works</A>
<hr>
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<span class="release-info">Release 0.04, documentation updated on October 4, 2002.</span>
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<META NAME="resource-type" CONTENT="document">
<META NAME="distribution" CONTENT="global">
<meta http-equiv="Content-Type" content="text/html; charset=">
<link rel="STYLESHEET" href="zodb.css">
<meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1">
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<link rel="first" href="zodb.html">
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<LINK REL="previous" HREF="node9.html">
<LINK REL="up" HREF="node8.html">
<LINK REL="next" HREF="node13.html">
<meta name='aesop' content='information'>
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......@@ -91,10 +92,16 @@ state.
<DT>Consistency</DT>
<DD>means that the data cannot be placed into a
logically invalid state; sanity checks can be written and enforced.
Usually this is done by defining a database schema, and requiring the
data always matches the schema. For example, this might enforce that
the <code>order_number</code> attribute is always an integer, and not a
string, tuple, or other object.
Usually this is done by defining a database schema, and requiring
the data always matches the schema. There are two typical
approaches to consistency. One is to enforce rules about the types
of objects and attribute; for example, enforce that the
<code>order_number</code> attribute is always an integer, and not a
string, tuple, or other object. Another is to guarantee consistency
across data structures; for example, that any object with an
<code>order_number</code> attribute must also appear in the
<code>orders_table</code> object. In general, atomicity and isolation make
it possible for applications to provide consistency.
<P>
</DD>
......@@ -148,7 +155,7 @@ has no way of enforcing consistency with a schema.
<b class="navlabel">Up:</b> <a class="sectref" HREF="node8.html">2 ZODB Programming</A>
<b class="navlabel">Next:</b> <a class="sectref" HREF="node13.html">2.3 Opening a ZODB</A>
<hr>
<span class="release-info">Release 0.03, documentation updated on February 8, 2002.</span>
<span class="release-info">Release 0.04, documentation updated on October 4, 2002.</span>
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<META NAME="resource-type" CONTENT="document">
<META NAME="distribution" CONTENT="global">
<meta http-equiv="Content-Type" content="text/html; charset=">
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<LINK REL="up" HREF="node8.html">
<LINK REL="next" HREF="node14.html">
<meta name='aesop' content='information'>
</head>
<body>
<DIV CLASS="navigation">
......@@ -65,7 +66,7 @@ implement the <tt class="class">Storage</tt> interface.
storing and retrieving objects from some form of long-term storage.
A few different types of Storage have been written, such as
<tt class="class">FileStorage</tt>, which uses regular disk files, and
<tt class="class">BerkeleyStorage</tt>, which uses Sleepycat Software's BerkeleyDB
<tt class="class">bsddb3Storage</tt>, which uses Sleepycat Software's BerkeleyDB
database. You could write a new Storage that stored objects in a
relational database or Metakit file, for example, if that would
better suit your application. Two example storages,
......@@ -81,7 +82,7 @@ implement the <tt class="class">Storage</tt> interface.
<P>
</LI>
<LI>Finally, the <tt class="class">Connection</tt> class caches objects, and moves
them into and out of object storage. A multi-threaded program can
them into and out of object storage. A multi-threaded program should
open a separate <tt class="class">Connection</tt> instance for each thread.
Different threads can then modify objects and commit their
modifications independently.
......@@ -97,13 +98,13 @@ a <tt class="class">Connection</tt> from the <tt class="class">DB instance</tt>.
code:
<P>
<dl><dd><pre class="verbatim">
<div class="verbatim"><pre>
from ZODB import FileStorage, DB
storage = FileStorage.FileStorage('/tmp/test-filestorage.fs')
db = DB(storage)
conn = db.open()
</pre></dl>
</pre></div>
<P>
Note that you can use a completely different data storage mechanism by
......@@ -141,7 +142,7 @@ you'll see how ZEO uses this flexibility to good effect.
<b class="navlabel">Up:</b> <a class="sectref" HREF="node8.html">2 ZODB Programming</A>
<b class="navlabel">Next:</b> <a class="sectref" HREF="node14.html">2.4 Writing a Persistent</A>
<hr>
<span class="release-info">Release 0.03, documentation updated on February 8, 2002.</span>
<span class="release-info">Release 0.04, documentation updated on October 4, 2002.</span>
</DIV>
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<META NAME="resource-type" CONTENT="document">
<META NAME="distribution" CONTENT="global">
<meta http-equiv="Content-Type" content="text/html; charset=">
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<LINK REL="previous" HREF="node13.html">
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<meta name='aesop' content='information'>
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......@@ -56,13 +57,13 @@ Making a Python class persistent is quite simple; it simply needs to
subclass from the <tt class="class">Persistent</tt> class, as shown in this example:
<P>
<dl><dd><pre class="verbatim">
<div class="verbatim"><pre>
import ZODB
from Persistence import Persistent
class User(Persistent):
pass
</pre></dl>
</pre></div>
<P>
The apparently unnecessary <code>import ZODB</code> statement is
......@@ -70,6 +71,11 @@ needed for the following <code>from...import</code> statement to work
correctly, since the ZODB code does some magical tricks with
importing.
<P>
The <tt class="class">Persistent</tt> base class is an <tt class="module">ExtensionClass</tt>
class. As a result, it not compatible with new-style classes or types
in Python 2.2 and up.
<P>
For simplicity, in the examples the <tt class="class">User</tt> class will
simply be used as a holder for a bunch of attributes. Normally the
......@@ -96,7 +102,7 @@ that will contain all the <tt class="class">User</tt> objects. (The
<tt class="class">BTree</tt> module is also included as part of Zope.)
<P>
<dl><dd><pre class="verbatim">
<div class="verbatim"><pre>
dbroot = conn.root()
# Ensure that a 'userdb' key is present
......@@ -106,7 +112,7 @@ if not dbroot.has_key('userdb'):
dbroot['userdb'] = BTree.BTree()
userdb = dbroot['userdb']
</pre></dl>
</pre></div>
<P>
Inserting a new user is simple: create the <tt class="class">User</tt> object, fill
......@@ -114,7 +120,7 @@ it with data, insert it into the <tt class="class">BTree</tt> instance, and comm
this transaction.
<P>
<dl><dd><pre class="verbatim"># Create new User instance
<div class="verbatim"><pre># Create new User instance
newuser = User()
# Add whatever attributes you want to track
......@@ -127,7 +133,7 @@ userdb[newuser.id] = newuser
# Commit the change
get_transaction().commit()
</pre></dl>
</pre></div>
<P>
When you import the ZODB package, it adds a new function,
......@@ -146,7 +152,7 @@ having transactional semantics for your program's variables, and you
can experiment with transactions at the Python interpreter's prompt:
<P>
<dl><dd><pre class="verbatim">&gt;&gt;&gt; newuser
<div class="verbatim"><pre>&gt;&gt;&gt; newuser
&lt;User instance at 81b1f40&gt;
&gt;&gt;&gt; newuser.first_name # Print initial value
'Andrew'
......@@ -156,7 +162,7 @@ can experiment with transactions at the Python interpreter's prompt:
&gt;&gt;&gt; get_transaction().abort() # Abort transaction
&gt;&gt;&gt; newuser.first_name # The value has changed back
'Andrew'
</pre></dl>
</pre></div>
<P>
......@@ -188,7 +194,7 @@ can experiment with transactions at the Python interpreter's prompt:
<b class="navlabel">Up:</b> <a class="sectref" HREF="node8.html">2 ZODB Programming</A>
<b class="navlabel">Next:</b> <a class="sectref" HREF="node15.html">2.5 Rules for Writing</A>
<hr>
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<span class="release-info">Release 0.04, documentation updated on October 4, 2002.</span>
</DIV>
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<meta name='aesop' content='information'>
</head>
<body>
<DIV CLASS="navigation">
......@@ -81,13 +82,6 @@ defined on ExtensionClasses. The most important ones are the
arithmetic operations: <tt class="method">__radd__</tt>, <tt class="method">__rsub__</tt>, and so
forth.
<P>
</LI>
<LI>Python's built-in <tt class="function">isinstance()</tt> and <tt class="function">issubclass()</tt>
functions don't work properly on ExtensionClasses. Solution: use
custom <tt class="function">isinstance()</tt> and <tt class="function">issubclass()</tt> functions
that handle ExtensionClasses correctly.
<P>
</LI>
<LI>Recent versions of the ZODB allow writing a class with
......@@ -111,8 +105,7 @@ Let's look at each of these rules in detail.
<UL>
<LI><A href="node16.html">2.5.1 Modifying Mutable Objects</a>
<LI><A href="node17.html">2.5.2 Some Special Methods Don't Work</a>
<LI><A href="node18.html">2.5.3 Fixing <tt class="function">isinstance</tt> and <tt class="function">issubclass</tt></a>
<LI><A href="node19.html">2.5.4 <tt class="method">__getattr__</tt>, <tt class="method">__delattr__</tt>, and <tt class="method">__setattr__</tt></a>
<LI><A href="node18.html">2.5.3 <tt class="method">__getattr__</tt>, <tt class="method">__delattr__</tt>, and <tt class="method">__setattr__</tt></a>
</ul>
<!--End of Table of Child-Links-->
......@@ -144,7 +137,7 @@ Let's look at each of these rules in detail.
<b class="navlabel">Up:</b> <a class="sectref" HREF="node8.html">2 ZODB Programming</A>
<b class="navlabel">Next:</b> <a class="sectref" HREF="node16.html">2.5.1 Modifying Mutable Objects</A>
<hr>
<span class="release-info">Release 0.03, documentation updated on February 8, 2002.</span>
<span class="release-info">Release 0.04, documentation updated on October 4, 2002.</span>
</DIV>
<!--End of Navigation Panel-->
......
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View file @ 243c4e27
......@@ -6,8 +6,8 @@
<META NAME="keywords" CONTENT="zodb">
<META NAME="resource-type" CONTENT="document">
<META NAME="distribution" CONTENT="global">
<meta http-equiv="Content-Type" content="text/html; charset=">
<link rel="STYLESHEET" href="zodb.css">
<meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1">
<link rel="STYLESHEET" href="zodb.css" type='text/css'>
<link rel="first" href="zodb.html">
<link rel="contents" href="contents.html" title="Contents">
......@@ -15,6 +15,7 @@
<LINK REL="previous" HREF="node15.html">
<LINK REL="up" HREF="node15.html">
<LINK REL="next" HREF="node17.html">
<meta name='aesop' content='information'>
</head>
<body>
<DIV CLASS="navigation">
......@@ -77,10 +78,10 @@ its dirty bit to true. This is done by setting the
<tt class="member">_p_changed</tt> attribute of the object to true:
<P>
<dl><dd><pre class="verbatim">
<div class="verbatim"><pre>
userobj.friends.append(otherUser)
userobj._p_changed = 1
</pre></dl>
</pre></div>
<P>
An obsolete way of doing this that's still supported is calling the
......@@ -98,11 +99,11 @@ an <tt class="method">add_friend()</tt> modifier method to the class. <tt class
would then look like this:
<P>
<dl><dd><pre class="verbatim">
<div class="verbatim"><pre>
def add_friend(self, friend):
self.friends.append(otherUser)
self._p_changed = 1
</pre></dl>
</pre></div>
<P>
Alternatively, you could use a ZODB-aware list or mapping type that
......@@ -141,7 +142,7 @@ and may make it into a future upstream release of Zope.
<b class="navlabel">Up:</b> <a class="sectref" HREF="node15.html">2.5 Rules for Writing</A>
<b class="navlabel">Next:</b> <a class="sectref" HREF="node17.html">2.5.2 Some Special Methods</A>
<hr>
<span class="release-info">Release 0.03, documentation updated on February 8, 2002.</span>
<span class="release-info">Release 0.04, documentation updated on October 4, 2002.</span>
</DIV>
<!--End of Navigation Panel-->
......
doc/guide/zodb/node17.html
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......@@ -6,8 +6,8 @@
<META NAME="keywords" CONTENT="zodb">
<META NAME="resource-type" CONTENT="document">
<META NAME="distribution" CONTENT="global">
<meta http-equiv="Content-Type" content="text/html; charset=">
<link rel="STYLESHEET" href="zodb.css">
<meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1">
<link rel="STYLESHEET" href="zodb.css" type='text/css'>
<link rel="first" href="zodb.html">
<link rel="contents" href="contents.html" title="Contents">
......@@ -15,6 +15,7 @@
<LINK REL="previous" HREF="node16.html">
<LINK REL="up" HREF="node15.html">
<LINK REL="next" HREF="node18.html">
<meta name='aesop' content='information'>
</head>
<body>
<DIV CLASS="navigation">
......@@ -42,7 +43,7 @@
</tr></table>
<b class="navlabel">Previous:</b> <a class="sectref" HREF="node16.html">2.5.1 Modifying Mutable Objects</A>
<b class="navlabel">Up:</b> <a class="sectref" HREF="node15.html">2.5 Rules for Writing</A>
<b class="navlabel">Next:</b> <a class="sectref" HREF="node18.html">2.5.3 Fixing isinstance and</A>
<b class="navlabel">Next:</b> <a class="sectref" HREF="node18.html">2.5.3 __getattr__, __delattr__, and</A>
<br><hr>
</DIV>
<!--End of Navigation Panel-->
......@@ -77,13 +78,13 @@ instances, which means that <code>type(obj) == types.InstanceType</code>.
The code inside the Python interpreter looks like this:
<P>
<dl><dd><pre class="verbatim">
<div class="verbatim"><pre>
/* Code to compare objects v and w */
if (PyInstance_Check(v) || PyInstance_Check(w))
return PyInstance_DoBinOp(v, w, "__cmp__", "__rcmp__", do_cmp);
/* Do usual Python comparison of v,w */
c = PyObject_Compare(v, w);
</pre></dl>
</pre></div>
<P>
While ExtensionClasses try to behave as much like regular Python
......@@ -120,9 +121,9 @@ will repair this.
</tr></table>
<b class="navlabel">Previous:</b> <a class="sectref" HREF="node16.html">2.5.1 Modifying Mutable Objects</A>
<b class="navlabel">Up:</b> <a class="sectref" HREF="node15.html">2.5 Rules for Writing</A>
<b class="navlabel">Next:</b> <a class="sectref" HREF="node18.html">2.5.3 Fixing isinstance and</A>
<b class="navlabel">Next:</b> <a class="sectref" HREF="node18.html">2.5.3 __getattr__, __delattr__, and</A>
<hr>
<span class="release-info">Release 0.03, documentation updated on February 8, 2002.</span>
<span class="release-info">Release 0.04, documentation updated on October 4, 2002.</span>
</DIV>
<!--End of Navigation Panel-->
......
doc/guide/zodb/node18.html
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<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
<html>
<head>
<title>2.5.3 Fixing isinstance and issubclass</title>
<META NAME="description" CONTENT="2.5.3 Fixing isinstance and issubclass">
<title>2.5.3 __getattr__, __delattr__, and __setattr__</title>
<META NAME="description" CONTENT="2.5.3 __getattr__, __delattr__, and __setattr__">
<META NAME="keywords" CONTENT="zodb">
<META NAME="resource-type" CONTENT="document">
<META NAME="distribution" CONTENT="global">
<meta http-equiv="Content-Type" content="text/html; charset=">
<link rel="STYLESHEET" href="zodb.css">
<meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1">
<link rel="STYLESHEET" href="zodb.css" type='text/css'>
<link rel="first" href="zodb.html">
<link rel="contents" href="contents.html" title="Contents">
<LINK REL="next" HREF="node19.html">
<LINK REL="previous" HREF="node17.html">
<LINK REL="up" HREF="node15.html">
<LINK REL="next" HREF="node19.html">
<meta name='aesop' content='information'>
</head>
<body>
<DIV CLASS="navigation">
......@@ -42,112 +42,24 @@
</tr></table>
<b class="navlabel">Previous:</b> <a class="sectref" HREF="node17.html">2.5.2 Some Special Methods</A>
<b class="navlabel">Up:</b> <a class="sectref" HREF="node15.html">2.5 Rules for Writing</A>
<b class="navlabel">Next:</b> <a class="sectref" HREF="node19.html">2.5.4 __getattr__, __delattr__, and</A>
<b class="navlabel">Next:</b> <a class="sectref" HREF="node19.html">2.6 Writing Persistent Classes</A>
<br><hr>
</DIV>
<!--End of Navigation Panel-->
<H3><A NAME="SECTION000353000000000000000">
2.5.3 Fixing <tt class="function">isinstance</tt> and <tt class="function">issubclass</tt></A>
2.5.3 <tt class="method">__getattr__</tt>, <tt class="method">__delattr__</tt>, and <tt class="method">__setattr__</tt></A>
</H3>
<P>
Python's built-in functions
<tt class="function">isinstance()</tt> and <tt class="function">issubclass</tt> don't
work on ExtensionClass instances, for much the same reason that
<tt class="method">__cmp__</tt> is never called; in some bits of the Python core code,
branches are taken only if an object is of the <tt class="class">InstanceType</tt>
type, and this can never be true for an ExtensionClass instance.
Python 2.1 tried to fix this, and changed these functions slightly in
an effort to make them work for ExtensionClasses; unfortunately, the
changes didn't work.
<P>
The solution is to use customized versions of these functions that
handle ExtensionClasses specially and fall back to the built-in
version otherwise. Here are the versions we've written at the MEMS Exchange:
<P>
<dl><dd><pre class="verbatim">
# The built-in 'isinstance()' and 'issubclass()' won't work on
# ExtensionClasses, so you have to use the versions supplied here.
# (But those versions work fine on regular instances and classes too,
# so you should *always* use them.)
def issubclass (class1, class2):
"""A version of 'issubclass' that works with extension classes
as well as regular Python classes.
"""
# Both class objects are regular Python classes, so use the
# built-in 'issubclass()'.
if type(class1) is ClassType and type(class2) is ClassType:
return __builtin__.issubclass(class1, class2)
# Both so-called class objects have a '__bases__' attribute: ie.,
# they aren't regular Python classes, but they sure look like them.
# Assume they are extension classes and reimplement what the builtin
# 'issubclass()' does behind the scenes.
elif hasattr(class1, '__bases__') and hasattr(class2, '__bases__'):
# XXX it appears that "ec.__class__ is type(ec)" for an
# extension class 'ec': could we/should we use this as an
# additional check for extension classes?
# Breadth-first traversal of class1's superclass tree. Order
# doesn't matter because we're just looking for a "yes/no"
# answer from the tree; if we were trying to resolve a name,
# order would be important!
stack = [class1]
while stack:
if stack[0] is class2:
return 1
stack.extend(list(stack[0].__bases__))
del stack[0]
else:
return 0
# Not a regular class, not an extension class: blow up for consistency
# with builtin 'issubclass()"
else:
raise TypeError, "arguments must be class or ExtensionClass objects"
# issubclass ()
def isinstance (object, klass):
"""A version of 'isinstance' that works with extension classes
as well as regular Python classes."""
if type(klass) is TypeType:
return __builtin__.isinstance(object, klass)
elif hasattr(object, '__class__'):
return issubclass(object.__class__, klass)
else:
return 0
</pre></dl>
<P>
I'd recommend putting these functions in a module that always gets
imported. The convention on my work project is to put them in
<span class="file">mems/lib/base.py</span>, which contains various fundamental classes
and functions for our system, and access them like this:
<P>
<dl><dd><pre class="verbatim">
from mems.lib import base
...
if base.isinstance(object, Class): ...
</pre></dl>
<P>
Don't insert the modified functions into Python's
<tt class="module">__builtin__</tt> module, or import just the
<tt class="function">isinstance()</tt> and <tt class="function">issubclass</tt> functions.
If you consistently use <tt class="function">base.isinstance()</tt>, then forgetting
to import the <tt class="module">base</tt> module will result in a
<tt class="exception">NameError</tt> exception. In the
case of a forgotten import, calling the functions directly would use
Python's built-in versions, leading to subtle bugs that might not be
noticed for some time.
Recent versions of ZODB allow writing persistent classes that have
<tt class="method">__getattr__</tt>, <tt class="method">__delattr__</tt>, or <tt class="method">__setattr__</tt>
methods. The one minor complication is that the machinery for
automatically detecting changes to the object is disabled while the
<tt class="method">__getattr__</tt>, <tt class="method">__delattr__</tt>, or <tt class="method">__setattr__</tt>
method is executing. This means that if the object is modified, the
object should be marked as dirty by setting the object's
<tt class="member">_p_changed</tt> method to true.
<P>
......@@ -177,9 +89,9 @@ noticed for some time.
</tr></table>
<b class="navlabel">Previous:</b> <a class="sectref" HREF="node17.html">2.5.2 Some Special Methods</A>
<b class="navlabel">Up:</b> <a class="sectref" HREF="node15.html">2.5 Rules for Writing</A>
<b class="navlabel">Next:</b> <a class="sectref" HREF="node19.html">2.5.4 __getattr__, __delattr__, and</A>
<b class="navlabel">Next:</b> <a class="sectref" HREF="node19.html">2.6 Writing Persistent Classes</A>
<hr>
<span class="release-info">Release 0.03, documentation updated on February 8, 2002.</span>
<span class="release-info">Release 0.04, documentation updated on October 4, 2002.</span>
</DIV>
<!--End of Navigation Panel-->
......
doc/guide/zodb/node19.html
View file @ 243c4e27
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
<html>
<head>
<title>2.5.4 __getattr__, __delattr__, and __setattr__</title>
<META NAME="description" CONTENT="2.5.4 __getattr__, __delattr__, and __setattr__">
<title>2.6 Writing Persistent Classes</title>
<META NAME="description" CONTENT="2.6 Writing Persistent Classes">
<META NAME="keywords" CONTENT="zodb">
<META NAME="resource-type" CONTENT="document">
<META NAME="distribution" CONTENT="global">
<meta http-equiv="Content-Type" content="text/html; charset=">
<link rel="STYLESHEET" href="zodb.css">
<meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1">
<link rel="STYLESHEET" href="zodb.css" type='text/css'>
<link rel="first" href="zodb.html">
<link rel="contents" href="contents.html" title="Contents">
<LINK REL="previous" HREF="node18.html">
<LINK REL="up" HREF="node15.html">
<LINK REL="previous" HREF="node15.html">
<LINK REL="up" HREF="node8.html">
<LINK REL="next" HREF="node20.html">
<meta name='aesop' content='information'>
</head>
<body>
<DIV CLASS="navigation">
......@@ -22,7 +23,7 @@
<td><A HREF="node18.html"><img src="/python/writing/icons/previous.gif"
border="0" height="32"
alt="Previous Page" width="32"></A></td>
<td><A HREF="node15.html"><img src="/python/writing/icons/up.gif"
<td><A HREF="node8.html"><img src="/python/writing/icons/up.gif"
border="0" height="32"
alt="Up One Level" width="32"></A></td>
<td><A HREF="node20.html"><img src="/python/writing/icons/next.gif"
......@@ -39,29 +40,33 @@
border="0" height="32"
alt="" width="32"></td>
</tr></table>
<b class="navlabel">Previous:</b> <a class="sectref" HREF="node18.html">2.5.3 Fixing isinstance and</A>
<b class="navlabel">Up:</b> <a class="sectref" HREF="node15.html">2.5 Rules for Writing</A>
<b class="navlabel">Next:</b> <a class="sectref" HREF="node20.html">2.6 Writing Persistent Classes</A>
<b class="navlabel">Previous:</b> <a class="sectref" HREF="node18.html">2.5.3 __getattr__, __delattr__, and</A>
<b class="navlabel">Up:</b> <a class="sectref" HREF="node8.html">2 ZODB Programming</A>
<b class="navlabel">Next:</b> <a class="sectref" HREF="node20.html">2.6.1 Changing Instance Attributes</A>
<br><hr>
</DIV>
<!--End of Navigation Panel-->
<H3><A NAME="SECTION000354000000000000000">
2.5.4 <tt class="method">__getattr__</tt>, <tt class="method">__delattr__</tt>, and <tt class="method">__setattr__</tt></A>
</H3>
<H2><A NAME="SECTION000360000000000000000">
2.6 Writing Persistent Classes</A>
</H2>
<P>
Recent versions of ZODB allow writing persistent classes that have
<tt class="method">__getattr__</tt>, <tt class="method">__delattr__</tt>, or <tt class="method">__setattr__</tt>
methods. The one minor complication is that the machinery for
automatically detecting changes to the object is disabled while the
<tt class="method">__getattr__</tt>, <tt class="method">__delattr__</tt>, or <tt class="method">__setattr__</tt>
method is executing. This means that if the object is modified, the
object should be marked as dirty by setting the object's
<tt class="member">_p_changed</tt> method to true.
Now that we've looked at the basics of programming using the ZODB,
we'll turn to some more subtle tasks that are likely to come up for
anyone using the ZODB in a production system.
<P>
<p><hr>
<!--Table of Child-Links-->
<A NAME="CHILD_LINKS"><STRONG>Subsections</STRONG></a>
<UL>
<LI><A href="node20.html">2.6.1 Changing Instance Attributes</a>
</ul>
<!--End of Table of Child-Links-->
<DIV CLASS="navigation">
<p><hr>
<table align="center" width="100%" cellpadding="0" cellspacing="2">
......@@ -69,7 +74,7 @@ object should be marked as dirty by setting the object's
<td><A HREF="node18.html"><img src="/python/writing/icons/previous.gif"
border="0" height="32"
alt="Previous Page" width="32"></A></td>
<td><A HREF="node15.html"><img src="/python/writing/icons/up.gif"
<td><A HREF="node8.html"><img src="/python/writing/icons/up.gif"
border="0" height="32"
alt="Up One Level" width="32"></A></td>
<td><A HREF="node20.html"><img src="/python/writing/icons/next.gif"
......@@ -86,11 +91,11 @@ object should be marked as dirty by setting the object's
border="0" height="32"
alt="" width="32"></td>
</tr></table>
<b class="navlabel">Previous:</b> <a class="sectref" HREF="node18.html">2.5.3 Fixing isinstance and</A>
<b class="navlabel">Up:</b> <a class="sectref" HREF="node15.html">2.5 Rules for Writing</A>
<b class="navlabel">Next:</b> <a class="sectref" HREF="node20.html">2.6 Writing Persistent Classes</A>
<b class="navlabel">Previous:</b> <a class="sectref" HREF="node18.html">2.5.3 __getattr__, __delattr__, and</A>
<b class="navlabel">Up:</b> <a class="sectref" HREF="node8.html">2 ZODB Programming</A>
<b class="navlabel">Next:</b> <a class="sectref" HREF="node20.html">2.6.1 Changing Instance Attributes</A>
<hr>
<span class="release-info">Release 0.03, documentation updated on February 8, 2002.</span>
<span class="release-info">Release 0.04, documentation updated on October 4, 2002.</span>
</DIV>
<!--End of Navigation Panel-->
......
doc/guide/zodb/node2.html
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......@@ -6,8 +6,8 @@
<META NAME="keywords" CONTENT="zodb">
<META NAME="resource-type" CONTENT="document">
<META NAME="distribution" CONTENT="global">
<meta http-equiv="Content-Type" content="text/html; charset=">
<link rel="STYLESHEET" href="zodb.css">
<meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1">
<link rel="STYLESHEET" href="zodb.css" type='text/css'>
<link rel="first" href="zodb.html">
<link rel="contents" href="contents.html" title="Contents">
......@@ -15,6 +15,7 @@
<LINK REL="previous" href="contents.html">
<LINK REL="up" HREF="zodb.html">
<LINK REL="next" HREF="node3.html">
<meta name='aesop' content='information'>
</head>
<body>
<DIV CLASS="navigation">
......@@ -100,7 +101,7 @@ of the guide is always available at
<b class="navlabel">Up:</b> <a class="sectref" HREF="zodb.html">ZODB/ZEO Programming Guide</A>
<b class="navlabel">Next:</b> <a class="sectref" HREF="node3.html">1.1 What is the</A>
<hr>
<span class="release-info">Release 0.03, documentation updated on February 8, 2002.</span>
<span class="release-info">Release 0.04, documentation updated on October 4, 2002.</span>
</DIV>
<!--End of Navigation Panel-->
......
doc/guide/zodb/node20.html
View file @ 243c4e27
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
<html>
<head>
<title>2.6 Writing Persistent Classes</title>
<META NAME="description" CONTENT="2.6 Writing Persistent Classes">
<title>2.6.1 Changing Instance Attributes</title>
<META NAME="description" CONTENT="2.6.1 Changing Instance Attributes">
<META NAME="keywords" CONTENT="zodb">
<META NAME="resource-type" CONTENT="document">
<META NAME="distribution" CONTENT="global">
<meta http-equiv="Content-Type" content="text/html; charset=">
<link rel="STYLESHEET" href="zodb.css">
<meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1">
<link rel="STYLESHEET" href="zodb.css" type='text/css'>
<link rel="first" href="zodb.html">
<link rel="contents" href="contents.html" title="Contents">
<LINK REL="previous" HREF="node15.html">
<LINK REL="up" HREF="node8.html">
<LINK REL="next" HREF="node21.html">
<LINK REL="previous" HREF="node19.html">
<LINK REL="up" HREF="node19.html">
<LINK REL="next" href="zeo.html">
<meta name='aesop' content='information'>
</head>
<body>
<DIV CLASS="navigation">
......@@ -22,10 +23,10 @@
<td><A HREF="node19.html"><img src="/python/writing/icons/previous.gif"
border="0" height="32"
alt="Previous Page" width="32"></A></td>
<td><A HREF="node8.html"><img src="/python/writing/icons/up.gif"
<td><A HREF="node19.html"><img src="/python/writing/icons/up.gif"
border="0" height="32"
alt="Up One Level" width="32"></A></td>
<td><A HREF="node21.html"><img src="/python/writing/icons/next.gif"
<td><A href="zeo.html"><img src="/python/writing/icons/next.gif"
border="0" height="32"
alt="Next Page" width="32"></A></td>
<td align="center" width="100%">ZODB/ZEO Programming Guide</td>
......@@ -39,33 +40,65 @@
border="0" height="32"
alt="" width="32"></td>
</tr></table>
<b class="navlabel">Previous:</b> <a class="sectref" HREF="node19.html">2.5.4 __getattr__, __delattr__, and</A>
<b class="navlabel">Up:</b> <a class="sectref" HREF="node8.html">2 ZODB Programming</A>
<b class="navlabel">Next:</b> <a class="sectref" HREF="node21.html">2.6.1 Changing Instance Attributes</A>
<b class="navlabel">Previous:</b> <a class="sectref" HREF="node19.html">2.6 Writing Persistent Classes</A>
<b class="navlabel">Up:</b> <a class="sectref" HREF="node19.html">2.6 Writing Persistent Classes</A>
<b class="navlabel">Next:</b> <a class="sectref" href="zeo.html">3 ZEO</A>
<br><hr>
</DIV>
<!--End of Navigation Panel-->
<H2><A NAME="SECTION000360000000000000000">
2.6 Writing Persistent Classes</A>
</H2>
<H3><A NAME="SECTION000361000000000000000">
2.6.1 Changing Instance Attributes</A>
</H3>
<P>
Now that we've looked at the basics of programming using the ZODB,
we'll turn to some more subtle tasks that are likely to come up for
anyone using the ZODB in a production system.
Ideally, before making a class persistent you would get its interface
right the first time, so that no attributes would ever need to be
added, removed, or have their interpretation change over time. It's a
worthy goal, but also an impractical one unless you're gifted with
perfect knowledge of the future. Such unnatural foresight can't be
required of any person, so you therefore have to be prepared to handle
such structural changes gracefully. In object-oriented database
terminology, this is a schema update. The ZODB doesn't have an actual
schema specification, but you're changing the software's expectations
of the data contained by an object, so you're implicitly changing the
schema.
<P>
One way to handle such a change is to write a one-time conversion
program that will loop over every single object in the database and
update them to match the new schema. This can be easy if your network
of object references is quite structured, making it easy to find all
the instances of the class being modified. For example, if all
<tt class="class">User</tt> objects can be found inside a single dictionary or
BTree, then it would be a simple matter to loop over every
<tt class="class">User</tt> instance with a <tt class="keyword">for</tt> statement.
This is more difficult if your object graph is less structured; if
<tt class="class">User</tt> objects can be found as attributes of any number of
different class instances, then there's no longer any easy way to find
them all, short of writing a generalized object traversal function
that would walk over every single object in a ZODB, checking each one
to see if it's an instance of <tt class="class">User</tt>.
<A NAME="tex2html1"
HREF="#foot262"><SUP>1</SUP></A>Some OODBs support a feature called extents, which allow quickly
finding all the instances of a given class, no matter where they are
in the object graph; unfortunately the ZODB doesn't offer extents as a
feature.
<p><hr>
<!--Table of Child-Links-->
<A NAME="CHILD_LINKS"><STRONG>Subsections</STRONG></a>
<P>
XXX Rest of section not written yet: __getstate__/__setstate__
<UL>
<LI><A href="node21.html">2.6.1 Changing Instance Attributes</a>
</ul>
<!--End of Table of Child-Links-->
<P>
<BR><HR><H4>Footnotes</H4>
<DL>
<DT><A NAME="foot262">...User.
</A><A NAME="foot262"
HREF="node20.html#tex2html1"><SUP>1</SUP></A>
<DD>XXX is there a convenience method for walking the object graph hiding
somewhere inside DC's code? Should there be a utility method for
doing this? Should I write one and include it in this section?
</DL>
<DIV CLASS="navigation">
<p><hr>
<table align="center" width="100%" cellpadding="0" cellspacing="2">
......@@ -73,10 +106,10 @@ anyone using the ZODB in a production system.
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......@@ -90,11 +123,11 @@ anyone using the ZODB in a production system.
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<hr>
<span class="release-info">Release 0.03, documentation updated on February 8, 2002.</span>
<span class="release-info">Release 0.04, documentation updated on October 4, 2002.</span>
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<H2><A NAME="SECTION000410000000000000000">
3.1 How ZEO Works</A>
</H2>
<P>
The ZODB, as I've described it so far, can only be used within a
single Python process (though perhaps with multiple threads). ZEO,
Zope Enterprise Objects, extends the ZODB machinery to provide access
to objects over a network. The name "Zope Enterprise Objects" is a
bit misleading; ZEO can be used to store Python objects and access
them in a distributed fashion without Zope ever entering the picture.
The combination of ZEO and ZODB is essentially a Python-specific
object database.
<P>
ZEO consists of about 6000 lines of Python code, excluding tests. The
code is relatively small because it contains only code for a TCP/IP
server, and for a new type of Storage, <tt class="class">ClientStorage</tt>.
<tt class="class">ClientStorage</tt> simply makes remote procedure calls to the
server, which then passes them on a regular <tt class="class">Storage</tt> class such
as <tt class="class">FileStorage</tt>. The following diagram lays out the system:
<P>
XXX insert diagram here later
<P>
Any number of processes can create a <tt class="class">ClientStorage</tt>
instance, and any number of threads in each process can be using that
instance. <tt class="class">ClientStorage</tt> aggressively caches objects
locally, so in order to avoid using stale data. The ZEO server sends
an invalidation message to all the connected <tt class="class">ClientStorage</tt>
instances on every write operation. The invalidation message contains
the object ID for each object that's been modified, letting the
<tt class="class">ClientStorage</tt> instances delete the old data for the
given object from their caches.
<P>
This design decision has some consequences you should be aware of.
First, while ZEO isn't tied to Zope, it was first written for use with
Zope, which stores HTML, images, and program code in the database. As
a result, reads from the database are <i>far</i> more frequent than
writes, and ZEO is therefore better suited for read-intensive
applications. If every <tt class="class">ClientStorage</tt> is writing to the
database all the time, this will result in a storm of invalidate
messages being sent, and this might take up more processing time than
the actual database operations themselves.<A NAME="tex2html2"
HREF="#foot429"><SUP>2</SUP></A>
<P>
On the other hand, for applications that have few writes in comparison
to the number of read accesses, this aggressive caching can be a major
win. Consider a Slashdot-like discussion forum that divides the load
among several Web servers. If news items and postings are represented
by objects and accessed through ZEO, then the most heavily accessed
objects - the most recent or most popular postings - will very
quickly wind up in the caches of the
<tt class="class">ClientStorage</tt> instances on the front-end servers. The
back-end ZEO server will do relatively little work, only being called
upon to return the occasional older posting that's requested, and to
send the occasional invalidate message when a new posting is added.
The ZEO server isn't going to be contacted for every single request,
so its workload will remain manageable.
<P>
<BR><HR><H4>Footnotes</H4>
<DL>
<DT><A NAME="foot429">... themselves.</A><A NAME="foot429"
HREF="node22.html#tex2html2"><SUP>2</SUP></A>
<DD>These messages are
small and sent in batches, so there would need to be a lot of writes
before it became a problem.
</DL>
<DIV CLASS="navigation">
<p><hr>
<table align="center" width="100%" cellpadding="0" cellspacing="2">
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<hr>
<span class="release-info">Release 0.04, documentation updated on October 4, 2002.</span>
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<META NAME="resource-type" CONTENT="document">
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<link rel="first" href="zodb.html">
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<td><A href="zeo.html"><img src="/python/writing/icons/previous.gif"
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<H2><A NAME="SECTION000410000000000000000">
3.1 How ZEO Works</A>
<H2><A NAME="SECTION000420000000000000000">
3.2 Installing ZEO</A>
</H2>
<P>
The ZODB, as I've described it so far, can only be used within a
single Python process (though perhaps with multiple threads). ZEO,
Zope Enterprise Objects, extends the ZODB machinery to provide access
to objects over a network. The name "Zope Enterprise Objects" is a
bit misleading; ZEO can be used to store Python objects and access
them in a distributed fashion without Zope ever entering the picture.
The combination of ZEO and ZODB is essentially a Python-specific
object database.
<P>
ZEO consists of about 1400 lines of Python code. The code is
relatively small because it contains only code for a TCP/IP server,
and for a new type of Storage, <tt class="class">ClientStorage</tt>.
<tt class="class">ClientStorage</tt> doesn't use disk files at all; it simply
makes remote procedure calls to the server, which then passes them on
a regular <tt class="class">Storage</tt> class such as <tt class="class">FileStorage</tt>. The
following diagram lays out the system:
<P>
XXX insert diagram here later
This section covers how to install the ZEO package, and how to
configure and run a ZEO Storage Server on a machine.
<P>
Any number of processes can create a <tt class="class">ClientStorage</tt>
instance, and any number of threads in each process can be using that
instance. <tt class="class">ClientStorage</tt> aggressively caches objects
locally, so in order to avoid using stale data, the ZEO server sends
an invalidate message to all the connected <tt class="class">ClientStorage</tt>
instances on every write operation. The invalidate message contains
the object ID for each object that's been modified, letting the
<tt class="class">ClientStorage</tt> instances delete the old data for the
given object from their caches.
<P>
This design decision has some consequences you should be aware of.
First, while ZEO isn't tied to Zope, it was first written for use with
Zope, which stores HTML, images, and program code in the database. As
a result, reads from the database are <i>far</i> more frequent than
writes, and ZEO is therefore better suited for read-intensive
applications. If every <tt class="class">ClientStorage</tt> is writing to the
database all the time, this will result in a storm of invalidate
messages being sent, and this might take up more processing time than
the actual database operations themselves.
<P>
On the other hand, for applications that have few writes in comparison
to the number of read accesses, this aggressive caching can be a major
win. Consider a Slashdot-like discussion forum that divides the load
among several Web servers. If news items and postings are represented
by objects and accessed through ZEO, then the most heavily accessed
objects - the most recent or most popular postings - will very
quickly wind up in the caches of the
<tt class="class">ClientStorage</tt> instances on the front-end servers. The
back-end ZEO server will do relatively little work, only being called
upon to return the occasional older posting that's requested, and to
send the occasional invalidate message when a new posting is added.
The ZEO server isn't going to be contacted for every single request,
so its workload will remain manageable.
<p><hr>
<!--Table of Child-Links-->
<A NAME="CHILD_LINKS"><STRONG>Subsections</STRONG></a>
<P>
<UL>
<LI><A href="node24.html">3.2.1 Requirements</a>
<LI><A href="node25.html">3.2.2 Running a server</a>
</ul>
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<table align="center" width="100%" cellpadding="0" cellspacing="2">
<tr>
<td><A href="zeo.html"><img src="/python/writing/icons/previous.gif"
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<td><A href="zeo.html"><img src="/python/writing/icons/up.gif"
......@@ -136,11 +92,11 @@ so its workload will remain manageable.
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<hr>
<span class="release-info">Release 0.03, documentation updated on February 8, 2002.</span>
<span class="release-info">Release 0.04, documentation updated on October 4, 2002.</span>
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<H2><A NAME="SECTION000420000000000000000">
3.2 Installing ZEO</A>
</H2>
<H3><A NAME="SECTION000421000000000000000">
3.2.1 Requirements</A>
</H3>
<P>
This section covers how to install the ZEO package, and how to
configure and run a ZEO Storage Server on a machine.
The ZEO server software is included in ZODB3. As with the rest of
ZODB3, you'll need Python 2.1 or higher.
<P>
<p><hr>
<!--Table of Child-Links-->
<A NAME="CHILD_LINKS"><STRONG>Subsections</STRONG></a>
<UL>
<LI><A href="node25.html">3.2.1 Requirements</a>
<LI><A href="node26.html">3.2.2 Installation</a>
</ul>
<!--End of Table of Child-Links-->
<DIV CLASS="navigation">
<p><hr>
<table align="center" width="100%" cellpadding="0" cellspacing="2">
......@@ -74,7 +65,7 @@ configure and run a ZEO Storage Server on a machine.
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<td><A HREF="node25.html"><img src="/python/writing/icons/next.gif"
......@@ -91,11 +82,11 @@ configure and run a ZEO Storage Server on a machine.
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<hr>
<span class="release-info">Release 0.03, documentation updated on February 8, 2002.</span>
<span class="release-info">Release 0.04, documentation updated on October 4, 2002.</span>
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<H3><A NAME="SECTION000421000000000000000">
3.2.1 Requirements</A>
<H3><A NAME="SECTION000422000000000000000">
3.2.2 Running a server</A>
</H3>
<P>
To run a ZEO server, you'll need Python 1.5.2 or 2.0, and the ZODB
packages from <a class="url" href="http://www.amk.ca/files/zodb/">http://www.amk.ca/files/zodb/</a>have to be installed.
<P>
<i>Note for Python 1.5.2 users</i>: ZEO requires updated versions
of the <tt class="module">asyncore.py</tt> and <tt class="module">asynchat.py</tt> modules that are
included in 1.5.2's standard library. Current versions of the ZODB
distribution install private versions of these modules, so you
shouldn't need to grab updated versions yourself. (The symptom of
this problem is a traceback on attempting to run a ZEO client program:
the traceback is ``TypeError: too many arguments; expected 2, got 3''
around line 100 of <span class="file">smac.py</span>.
The start.py script in the ZEO directory can be used to start a
server. Run it with the -h option to see the various values. If
you're just experimenting, a good choise is to use
<code>python ZEO/start.py -D -U /tmp/zeosocket</code> to run ZEO in
debug mode and with a Unix domain socket.
<P>
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<H3><A NAME="SECTION000422000000000000000">
3.2.2 Installation</A>
</H3>
<H2><A NAME="SECTION000430000000000000000">
3.3 Testing the ZEO Installation</A>
</H2>
<P>
Once a ZEO server is up and running, using it is just like using ZODB
with a more conventional disk-based storage; no new programming
details are introduced by using a remote server. The only difference
is that programs must create a <tt class="class">ClientStorage</tt> instance instead
of a <tt class="class">FileStorage</tt> instance. From that point onward, ZODB-based
code is happily unaware that objects are being retrieved from a ZEO
server, and not from the local disk.
<P>
As an example, and to test whether ZEO is working correctly, try
running the following lines of code, which will connect to the server,
add some bits of data to the root of the ZODB, and commits the
transaction:
<P>
<div class="verbatim"><pre>
from ZEO import ClientStorage
from ZODB import DB
# Change next line to connect to your ZEO server
addr = ('kronos.example.com', 1975)
storage = ClientStorage.ClientStorage(addr)
db = DB(storage)
conn = db.open()
root = conn.root()
# Store some things in the root
root['list'] = ['a', 'b', 1.0, 3]
root['dict'] = {'a':1, 'b':4}
# Commit the transaction
get_transaction().commit()
</pre></div>
<P>
Installing the ZEO package is easy. Just run <code>python setup.py
install</code>. This will install the ZEO/ package into your Python
installation, and copy various files into their proper locations:
<span class="file">zeo.conf</span> will be put into <span class="file">/usr/local/etc/</span>, a <span class="file">zeo</span> startup
script will be put in <span class="file">/etc/rc.d/init.d/</span>, and the <span class="file">zeod</span>
daemon program will be placed in <span class="file">/usr/local/bin</span>.
If this code runs properly, then your ZEO server is working correctly.
<P>
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<H2><A NAME="SECTION000430000000000000000">
3.3 Configuring and Running a ZEO Server</A>
<H2><A NAME="SECTION000440000000000000000">
3.4 ZEO Programming Notes</A>
</H2>
<P>
Edit <code>/usr/local/etc/zeo.conf</code> appropriately for your desired
setup. This configuration file controls the port on which ZEO will
listen for connections, the user and group IDs under which the server
will be executed, and the location of the concrete <tt class="class">Storage</tt>
object that will be made network-accessible.
ZEO is written using <tt class="module">asyncore</tt>, from the Python standard
library. It assumes that some part of the user application is running
an <tt class="module">asyncore</tt> mainloop. For example, Zope run the loop in a
separate thread and ZEO uses that. If your application does not have
a mainloop, ZEO will not process incoming invalidation messages until
you make some call into ZEO. The <tt class="method">Connection.sync</tt> method can
be used to process pending invalidation messages. You can call it
when you want to make sure the <tt class="class">Connection</tt> has the most recent
version of every object, but you don't have any other work for ZEO to do.
<P>
......@@ -84,11 +89,11 @@ object that will be made network-accessible.
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3.4 Testing the ZEO Installation</A>
<H2><A NAME="SECTION000450000000000000000">
3.5 Sample Application: chatter.py</A>
</H2>
<P>
Once a ZEO server is up and running, using it is just like using ZODB
with a more conventional disk-based storage; no new programming
details are introduced by using a remote server. The only difference
is that programs must create a <tt class="class">ClientStorage</tt> instance instead
of a <tt class="class">FileStorage</tt> instance. From that point onward, ZODB-based
code is happily unaware that objects are being retrieved from a ZEO
server, and not from the local disk.
For an example application, we'll build a little chat application.
What's interesting is that none of the application's code deals with
network programming at all; instead, an object will hold chat
messages, and be magically shared between all the clients through ZEO.
I won't present the complete script here; it's included in my ZODB
distribution, and you can download it from
<a class="url" href="http://www.amk.ca/zodb/demos/">http://www.amk.ca/zodb/demos/</a>. Only the interesting portions of
the code will be covered here.
<P>
The basic data structure is the <tt class="class">ChatSession</tt> object,
which provides an <tt class="method">add_message()</tt> method that adds a
message, and a <tt class="method">new_messages()</tt> method that returns a list
of new messages that have accumulated since the last call to
<tt class="method">new_messages()</tt>. Internally, <tt class="class">ChatSession</tt>
maintains a B-tree that uses the time as the key, and stores the
message as the corresponding value.
<P>
The constructor for <tt class="class">ChatSession</tt> is pretty simple; it simply
creates an attribute containing a B-tree:
<P>
<div class="verbatim"><pre>
class ChatSession(Persistent):
def __init__(self, name):
self.name = name
# Internal attribute: _messages holds all the chat messages.
self._messages = BTrees.OOBTree.OOBTree()
</pre></div>
<P>
<tt class="method">add_message()</tt> has to add a message to the
<code>_messages</code> B-tree. A complication is that it's possible
that some other client is trying to add a message at the same time;
when this happens, the client that commits first wins, and the second
client will get a <tt class="exception">ConflictError</tt> exception when it tries to
commit. For this application, <tt class="exception">ConflictError</tt> isn't serious
but simply means that the operation has to be retried; other
applications might treat it as a fatal error. The code uses
<code>try...except...else</code> inside a <code>while</code> loop,
breaking out of the loop when the commit works without raising an
exception.
<P>
<div class="verbatim"><pre>
def add_message(self, message):
"""Add a message to the channel.
message -- text of the message to be added
"""
while 1:
try:
now = time.time()
self._messages[now] = message
get_transaction().commit()
except ConflictError:
# Conflict occurred; this process should pause and
# wait for a little bit, then try again.
time.sleep(.2)
pass
else:
# No ConflictError exception raised, so break
# out of the enclosing while loop.
break
# end while
</pre></div>
<P>
<tt class="method">new_messages()</tt> introduces the use of <i>volatile</i>
attributes. Attributes of a persistent object that begin with
<code>_v_</code> are considered volatile and are never stored in the
database. <tt class="method">new_messages()</tt> needs to store the last time
the method was called, but if the time was stored as a regular
attribute, its value would be committed to the database and shared
with all the other clients. <tt class="method">new_messages()</tt> would then
return the new messages accumulated since any other client called
<tt class="method">new_messages()</tt>, which isn't what we want.
<P>
<div class="verbatim"><pre>
def new_messages(self):
"Return new messages."
# self._v_last_time is the time of the most recent message
# returned to the user of this class.
if not hasattr(self, '_v_last_time'):
self._v_last_time = 0
new = []
T = self._v_last_time
for T2, message in self._messages.items():
if T2 &gt; T:
new.append(message)
self._v_last_time = T2
return new
</pre></div>
<P>
As an example, and to test whether ZEO is working correctly, try
running the following lines of code, which will connect to the server,
add some bits of data to the root of the ZODB, and commits the
transaction:
This application is interesting because it uses ZEO to easily share a
data structure; ZEO and ZODB are being used for their networking
ability, not primarily for their data storage ability. I can foresee
many interesting applications using ZEO in this way:
<P>
<dl><dd><pre class="verbatim">
from ZEO import ClientStorage
from ZODB import DB
# Change next line to connect to your ZEO server
addr = ('kronos.example.com', 1975)
storage = ClientStorage.ClientStorage(addr)
db = DB(storage)
conn = db.open()
root = conn.root()
<UL>
<LI>With a Tkinter front-end, and a cleverer, more scalable data
structure, you could build a shared whiteboard using the same
technique.
<P>
</LI>
<LI>A shared chessboard object would make writing a networked chess
game easy.
# Store some things in the root
root['list'] = ['a', 'b', 1.0, 3]
root['dict'] = {'a':1, 'b':4}
<P>
</LI>
<LI>You could create a Python class containing a CD's title and
track information. To make a CD database, a read-only ZEO server
could be opened to the world, or an HTTP or XML-RPC interface could
be written on top of the ZODB.
# Commit the transaction
get_transaction().commit()
</pre></dl>
<P>
</LI>
<LI>A program like Quicken could use a ZODB on the local disk to
store its data. This avoids the need to write and maintain
specialized I/O code that reads in your objects and writes them out;
instead you can concentrate on the problem domain, writing objects
that represent cheques, stock portfolios, or whatever.
<P>
If this code runs properly, then your ZEO server is working correctly.
</LI>
</UL>
<P>
......@@ -115,11 +215,11 @@ If this code runs properly, then your ZEO server is working correctly.
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<span class="release-info">Release 0.04, documentation updated on October 4, 2002.</span>
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3.5 ZEO Programming Notes</A>
</H2>
<H1><A NAME="SECTION000500000000000000000">
4 Transactions and Versioning</A>
</H1>
<P>
XXX The Connection.sync() method and its necessity (if it works at all!)
<P>
<p><hr>
<!--Table of Child-Links-->
<A NAME="CHILD_LINKS"><STRONG>Subsections</STRONG></a>
<UL>
<LI><A href="node30.html">4.1 Subtransactions</a>
<LI><A href="node31.html">4.2 Undoing Changes</a>
<LI><A href="node32.html">4.3 Versions</a>
<LI><A href="node33.html">4.4 Multithreaded ZODB Programs</a>
</ul>
<!--End of Table of Child-Links-->
<DIV CLASS="navigation">
<p><hr>
......@@ -63,7 +73,7 @@ XXX The Connection.sync() method and its necessity (if it works at all!)
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......@@ -80,11 +90,11 @@ XXX The Connection.sync() method and its necessity (if it works at all!)
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......@@ -6,8 +6,8 @@
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<META NAME="resource-type" CONTENT="document">
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......@@ -15,6 +15,7 @@
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......@@ -106,7 +107,7 @@ accessed in a while.
<b class="navlabel">Up:</b> <a class="sectref" HREF="node2.html">1 Introduction</A>
<b class="navlabel">Next:</b> <a class="sectref" HREF="node4.html">1.2 OODBs vs. Relational</A>
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<H1><A NAME="SECTION000500000000000000000">
4 Transactions and Versioning</A>
</H1>
<H2><A NAME="SECTION000520000000000000000">
4.2 Undoing Changes</A>
</H2>
<P>
Some types of <tt class="class">Storage</tt> support undoing a transaction even after
it's been committed. You can tell if this is the case by calling the
<tt class="method">supportsUndo()</tt> method of the <tt class="class">DB</tt> instance, which
returns true if the underlying storage supports undo. Alternatively
you can call the <tt class="method">supportsUndo()</tt> method on the underlying
storage instance.
<p><hr>
<!--Table of Child-Links-->
<A NAME="CHILD_LINKS"><STRONG>Subsections</STRONG></a>
<P>
If a database supports undo, then the <tt class="method">undoLog(<var>start</var>,
<var>end</var><big>[</big>, func<big>]</big>)</tt> method on the <tt class="class">DB</tt> instance returns
the log of past transactions, returning transactions between the times
<var>start</var> and <var>end</var>, measured in seconds from the epoch.
If present, <var>func</var> is a function that acts as a filter on the
transactions to be returned; it's passed a dictionary representing
each transaction, and only transactions for which <var>func</var> returns
true will be included in the list of transactions returned to the
caller of <tt class="method">undoLog()</tt>. The dictionary contains keys for
various properties of the transaction. The most important keys are
"<tt class="samp">id</tt>", for the transaction ID, and "<tt class="samp">time</tt>", for the time at
which the transaction was committed.
<P>
<div class="verbatim"><pre>
&gt;&gt;&gt; print storage.undoLog(0, sys.maxint)
[{'description': '',
'id': 'AzpGEGqU/0QAAAAAAAAGMA',
'time': 981126744.98,
'user_name': ''},
{'description': '',
'id': 'AzpGC/hUOKoAAAAAAAAFDQ',
'time': 981126478.202,
'user_name': ''}
...
</pre></div>
<P>
To store a description and a user name on a commit, get the current
transaction and call the <tt class="method">note(<var>text</var>)</tt> method to store a
description, and the
<tt class="method">setUser(<var>user_name</var>)</tt> method to store the user name.
While <tt class="method">setUser()</tt> overwrites the current user name and replaces
it with the new value, the <tt class="method">note()</tt> method always adds the text
to the transaction's description, so it can be called several times to
log several different changes made in the course of a single
transaction.
<UL>
<LI><A href="node32.html">4.1 Subtransactions</a>
<LI><A href="node33.html">4.2 Undoing Changes</a>
<LI><A href="node34.html">4.3 Versions</a>
<LI><A href="node35.html">4.4 Multithreaded ZODB Programs</a>
</ul>
<!--End of Table of Child-Links-->
<P>
<div class="verbatim"><pre>
get_transaction().setUser('amk')
get_transaction().note('Change ownership')
</pre></div>
<P>
To undo a transaction, call the <tt class="method">DB.undo(<var>id</var>)</tt> method,
passing it the ID of the transaction to undo. If the transaction
can't be undone, a <tt class="exception">ZODB.POSException.UndoError</tt> exception
will be raised, with the message ``non-undoable
transaction''. Usually this will happen because later transactions
modified the objects affected by the transaction you're trying to
undo.
<P>
After you call <tt class="method">undo()</tt> you must commit the transaction for the
undo to actually be applied.
<A NAME="tex2html3"
HREF="#foot583"><SUP>3</SUP></A> There is one glitch in the undo process. The thread
that calls undo may not see the changes to the object until it calls
<tt class="method">Connection.sync()</tt> or commits another transaction.
<P>
<BR><HR><H4>Footnotes</H4>
<DL>
<DT><A NAME="foot583">... applied.</A><A NAME="foot583"
HREF="node31.html#tex2html3"><SUP>3</SUP></A>
<DD>There are actually two different ways a storage can
implement the undo feature. Most of the storages that ship with ZODB
use the transactional form of undo described in the main text. Some
storages may use a non-transactional undo makes changes visible
immediately.
</DL>
<DIV CLASS="navigation">
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<span class="release-info">Release 0.04, documentation updated on October 4, 2002.</span>
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<H2><A NAME="SECTION000510000000000000000">
4.1 Subtransactions</A>
<H2><A NAME="SECTION000530000000000000000">
4.3 Versions</A>
</H2>
<P>
Subtransactions can be created within a transaction. Each
subtransaction can be individually committed and aborted, but the
changes within a subtransaction are not truly committed until the
containing transaction is committed.
While many subtransactions can be contained within a single regular
transaction, it's also possible to contain many regular transactions
within a long-running transaction, called a version in ZODB
terminology. Inside a version, any number of transactions can be
created and committed or rolled back, but the changes within a version
are not made visible to other connections to the same ZODB.
<P>
The primary purpose of subtransactions is to decrease the memory usage
of transactions that touch a very large number of objects. Consider a
transaction during which 200,000 objects are modified. All the
objects that are modified in a single transaction have to remain in
memory until the transaction is committed, because the ZODB can't
discard them from the object cache. This can potentially make the
memory usage quite large. With subtransactions, a commit can be be
performed at intervals, say, every 10,000 objects. Those 10,000
objects are then written to permanent storage and can be purged from
the cache to free more space.
Not all storages support versions, but you can test for versioning
ability by calling <tt class="method">supportsVersions()</tt> method of the
<tt class="class">DB</tt> instance, which returns true if the underlying storage
supports versioning.
<P>
To commit a subtransaction instead of a full transaction,
pass a true value to the <tt class="method">commit()</tt>
or <tt class="method">abort()</tt> method of the <tt class="class">Transaction</tt> object.
A version can be selected when creating the <tt class="class">Connection</tt>
instance using the <tt class="method">DB.open(<big>[</big><var>version</var><big>]</big>)</tt> method.
The <var>version</var> argument must be a string that will be used as the
name of the version.
<P>
<dl><dd><pre class="verbatim">
# Commit a subtransaction
get_transaction().commit(1)
<div class="verbatim"><pre>
vers_conn = db.open(version='Working version')
</pre></div>
# Abort a subtransaction
get_transaction().abort(1)
</pre></dl>
<P>
Transactions can then be committed and aborted using this versioned
connection. Other connections that don't specify a version, or
provide a different version name, will not see changes committed
within the version named "<tt class="samp">Working&nbsp;version</tt>". To commit or abort a
version, which will either make the changes visible to all clients or
roll them back, call the <tt class="method">DB.commitVersion()</tt> or
<tt class="method">DB.abortVersion()</tt> methods.
XXX what are the source and dest arguments for?
<P>
The ZODB makes no attempt to reconcile changes between different
versions. Instead, the first version which modifies an object will
gain a lock on that object. Attempting to modify the object from a
different version or from an unversioned connection will cause a
<tt class="exception">ZODB.POSException.VersionLockError</tt> to be raised:
<P>
<div class="verbatim"><pre>
from ZODB.POSException import VersionLockError
try:
get_transaction().commit()
except VersionLockError, (obj_id, version):
print ('Cannot commit; object %s '
'locked by version %s' % (obj_id, version))
</pre></div>
<P>
A new subtransaction is automatically started on committing or
aborting the previous subtransaction.
The exception provides the ID of the locked object, and the name of
the version having a lock on it.
<P>
......@@ -96,7 +118,7 @@ aborting the previous subtransaction.
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......@@ -113,11 +135,11 @@ aborting the previous subtransaction.
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<hr>
<span class="release-info">Release 0.03, documentation updated on February 8, 2002.</span>
<span class="release-info">Release 0.04, documentation updated on October 4, 2002.</span>
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<META NAME="description" CONTENT="4.2 Undoing Changes">
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<H2><A NAME="SECTION000520000000000000000">
4.2 Undoing Changes</A>
<H2><A NAME="SECTION000540000000000000000">
4.4 Multithreaded ZODB Programs</A>
</H2>
<P>
Some types of <tt class="class">Storage</tt> support undoing a transaction even after
it's been committed. You can tell if this is the case by calling the
<tt class="method">supportsUndo()</tt> method of the <tt class="class">DB</tt> instance, which
returns true if the underlying storage supports undo. Alternatively
you can call the <tt class="method">supportsUndo()</tt> method on the underlying
storage instance.
<P>
If a database supports undo, then the <tt class="method">undoLog(<var>start</var>,
<var>end</var><big>[</big>, func<big>]</big>)</tt> method on the <tt class="class">DB</tt> instance returns
the log of past transactions, returning transactions between the times
<var>start</var> and <var>end</var>, measured in seconds from the epoch.
If present, <var>func</var> is a function that acts as a filter on the
transactions to be returned; it's passed a dictionary representing
each transaction, and only transactions for which <var>func</var> returns
true will be included in the list of transactions returned to the
caller of <tt class="method">undoLog()</tt>. The dictionary contains keys for
various properties of the transaction. The most important keys are
"<tt class="samp">id</tt>", for the transaction ID, and "<tt class="samp">time</tt>", for the time at
which the transaction was committed.
<P>
<dl><dd><pre class="verbatim">
&gt;&gt;&gt; print storage.undoLog(0, sys.maxint)
[{'description': '',
'id': 'AzpGEGqU/0QAAAAAAAAGMA',
'time': 981126744.98,
'user_name': ''},
{'description': '',
'id': 'AzpGC/hUOKoAAAAAAAAFDQ',
'time': 981126478.202,
'user_name': ''}
...
</pre></dl>
<P>
To store a description and a user name on a commit, get the current
transaction and call the <tt class="method">note(<var>text</var>)</tt> method to store a
description, and the
<tt class="method">setUser(<var>user_name</var>)</tt> method to store the user name.
While <tt class="method">setUser()</tt> overwrites the current user name and replaces
it with the new value, the <tt class="method">note()</tt> method always adds the text
to the transaction's description, so it can be called several times to
log several different changes made in the course of a single
transaction.
<P>
<dl><dd><pre class="verbatim">
get_transaction().setUser('amk')
get_transaction().note('Change ownership')
</pre></dl>
<P>
To undo a transaction, call the <tt class="method">DB.undo(<var>id</var>)</tt> method,
passing it the ID of the transaction to undo. If the transaction
can't be undone, a <tt class="exception">ZODB.POSException.UndoError</tt> exception
will be raised, with the message ``non-undoable
transaction''. Usually this will happen because later transactions
modified the objects affected by the transaction you're trying to
undo.
ZODB databases can be accessed from multithreaded Python programs.
The <tt class="class">Storage</tt> and <tt class="class">DB</tt> instances can be shared among
several threads, as long as individual <tt class="class">Connection</tt> instances
are created for each thread.
<P>
......@@ -122,7 +66,7 @@ undo.
<td><A HREF="node32.html"><img src="/python/writing/icons/previous.gif"
border="0" height="32"
alt="Previous Page" width="32"></A></td>
<td><A HREF="node31.html"><img src="/python/writing/icons/up.gif"
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border="0" height="32"
alt="Up One Level" width="32"></A></td>
<td><A HREF="node34.html"><img src="/python/writing/icons/next.gif"
......@@ -139,11 +83,11 @@ undo.
border="0" height="32"
alt="" width="32"></td>
</tr></table>
<b class="navlabel">Previous:</b> <a class="sectref" HREF="node32.html">4.1 Subtransactions</A>
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<hr>
<span class="release-info">Release 0.03, documentation updated on February 8, 2002.</span>
<span class="release-info">Release 0.04, documentation updated on October 4, 2002.</span>
</DIV>
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<td><A HREF="node31.html"><img src="/python/writing/icons/up.gif"
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border="0" height="32"
alt="Up One Level" width="32"></A></td>
<td><A HREF="node35.html"><img src="/python/writing/icons/next.gif"
......@@ -40,75 +41,33 @@
border="0" height="32"
alt="" width="32"></td>
</tr></table>
<b class="navlabel">Previous:</b> <a class="sectref" HREF="node33.html">4.2 Undoing Changes</A>
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<H2><A NAME="SECTION000530000000000000000">
4.3 Versions</A>
</H2>
<P>
While many subtransactions can be contained within a single regular
transaction, it's also possible to contain many regular transactions
within a long-running transaction, called a version in ZODB
terminology. Inside a version, any number of transactions can be
created and committed or rolled back, but the changes within a version
are not made visible to other connections to the same ZODB.
<P>
Not all storages support versions, but you can test for versioning
ability by calling <tt class="method">supportsVersions()</tt> method of the
<tt class="class">DB</tt> instance, which returns true if the underlying storage
supports versioning.
<P>
A version can be selected when creating the <tt class="class">Connection</tt>
instance using the <tt class="method">DB.open(<big>[</big><var>version</var><big>]</big>)</tt> method.
The <var>version</var> argument must be a string that will be used as the
name of the version.
<H1><A NAME="SECTION000600000000000000000">
5 Related Modules</A>
</H1>
<P>
<dl><dd><pre class="verbatim">
vers_conn = db.open(version='Working version')
</pre></dl>
The ZODB package includes a number of related modules that provide
useful data types such as BTrees.
<P>
Transactions can then be committed and aborted using this versioned
connection. Other connections that don't specify a version, or
provide a different version name, will not see changes committed
within the version named "<tt class="samp">Working&nbsp;version</tt>". To commit or abort a
version, which will either make the changes visible to all clients or
roll them back, call the <tt class="method">DB.commitVersion()</tt> or
<tt class="method">DB.abortVersion()</tt> methods.
XXX what are the source and dest arguments for?
<P>
The ZODB makes no attempt to reconcile changes between different
versions. Instead, the first version which modifies an object will
gain a lock on that object. Attempting to modify the object from a
different version or from an unversioned connection will cause a
<tt class="exception">ZODB.POSException.VersionLockError</tt> to be raised:
<P>
<dl><dd><pre class="verbatim">
from ZODB.POSException import VersionLockError
try:
get_transaction().commit()
except VersionLockError, (obj_id, version):
print ('Cannot commit; object %s '
'locked by version %s' % (obj_id, version))
</pre></dl>
<P>
The exception provides the ID of the locked object, and the name of
the version having a lock on it.
<p><hr>
<!--Table of Child-Links-->
<A NAME="CHILD_LINKS"><STRONG>Subsections</STRONG></a>
<P>
<UL>
<LI><A href="node35.html">5.1 <tt class="module">ZODB.PersistentMapping</tt></a>
<LI><A href="node36.html">5.2 <tt class="module">ZODB.PersistentList</tt></a>
<LI><A href="node37.html">5.3 BTrees Package</a>
</ul>
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<DIV CLASS="navigation">
<p><hr>
......@@ -117,7 +76,7 @@ the version having a lock on it.
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<td><A HREF="node35.html"><img src="/python/writing/icons/next.gif"
......@@ -134,11 +93,11 @@ the version having a lock on it.
border="0" height="32"
alt="" width="32"></td>
</tr></table>
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<b class="navlabel">Up:</b> <a class="sectref" HREF="zodb.html">ZODB/ZEO Programming Guide</A>
<b class="navlabel">Next:</b> <a class="sectref" HREF="node35.html">5.1 ZODB.PersistentMapping</A>
<hr>
<span class="release-info">Release 0.03, documentation updated on February 8, 2002.</span>
<span class="release-info">Release 0.04, documentation updated on October 4, 2002.</span>
</DIV>
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<html>
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<title>5.1 ZODB.PersistentMapping</title>
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<td><A HREF="node31.html"><img src="/python/writing/icons/up.gif"
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border="0" height="32"
alt="Up One Level" width="32"></A></td>
<td><A HREF="node36.html"><img src="/python/writing/icons/next.gif"
......@@ -39,26 +41,33 @@
border="0" height="32"
alt="" width="32"></td>
</tr></table>
<b class="navlabel">Previous:</b> <a class="sectref" HREF="node34.html">4.3 Versions</A>
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<H2><A NAME="SECTION000540000000000000000">
4.4 Multithreaded ZODB Programs</A>
<H2><A NAME="SECTION000610000000000000000">
5.1 <tt class="module">ZODB.PersistentMapping</tt></A>
</H2>
<P>
ZODB databases can be accessed from multithreaded Python programs.
The <tt class="class">Storage</tt> and <tt class="class">DB</tt> instances can be shared among
several threads, as long as individual <tt class="class">Connection</tt> instances
are created for each thread.
The <tt class="class">PersistentMapping</tt> class is a wrapper for mapping objects
that will set the dirty bit when the mapping is modified by setting or
deleting a key.
<P>
<dl><dt><b><a name="l2h-1"><tt class="function">PersistentMapping</tt></a></b>(<var>container = {}</var>)
<dd>
Create a <tt class="class">PersistentMapping</tt> object that wraps the
mapping object <var>container</var>. If you don't specify a
value for <var>container</var>, a regular Python dictionary is used.
</dl>
<P>
XXX I can't think of anything else to say about multithreaded ZODB
programs. Suggestions? An example program?
<tt class="class">PersistentMapping</tt> objects support all the same methods as
Python dictionaries do.
<P>
......@@ -69,7 +78,7 @@ programs. Suggestions? An example program?
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<td><A HREF="node36.html"><img src="/python/writing/icons/next.gif"
......@@ -86,11 +95,11 @@ programs. Suggestions? An example program?
border="0" height="32"
alt="" width="32"></td>
</tr></table>
<b class="navlabel">Previous:</b> <a class="sectref" HREF="node34.html">4.3 Versions</A>
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<b class="navlabel">Next:</b> <a class="sectref" HREF="node36.html">5.2 ZODB.PersistentList</A>
<hr>
<span class="release-info">Release 0.03, documentation updated on February 8, 2002.</span>
<span class="release-info">Release 0.04, documentation updated on October 4, 2002.</span>
</DIV>
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border="0" height="32"
alt="Previous Page" width="32"></A></td>
<td><A HREF="zodb.html"><img src="/python/writing/icons/up.gif"
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border="0" height="32"
alt="Up One Level" width="32"></A></td>
<td><A HREF="node37.html"><img src="/python/writing/icons/next.gif"
......@@ -40,33 +41,34 @@
border="0" height="32"
alt="" width="32"></td>
</tr></table>
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<H1><A NAME="SECTION000600000000000000000">
5 Related Modules</A>
</H1>
<H2><A NAME="SECTION000620000000000000000">
5.2 <tt class="module">ZODB.PersistentList</tt></A>
</H2>
<P>
The ZODB package includes a number of related modules that provide
useful data types such as BTrees or full-text indexes.
The <tt class="class">PersistentList</tt> class is a wrapper for mutable sequence objects,
much as <tt class="class">PersistentMapping</tt> is a wrapper for mappings.
<P>
<dl><dt><b><a name="l2h-2"><tt class="function">PersistentList</tt></a></b>(<var>initlist = []</var>)
<dd>
Create a <tt class="class">PersistentList</tt> object that wraps the
mutable sequence object <var>initlist</var>. If you don't specify a
value for <var>initlist</var>, a regular Python list is used.
</dl>
<p><hr>
<!--Table of Child-Links-->
<A NAME="CHILD_LINKS"><STRONG>Subsections</STRONG></a>
<P>
<tt class="class">PersistentList</tt> objects support all the same methods as
Python lists do.
<UL>
<LI><A href="node37.html">5.1 <tt class="module">ZODB.PersistentMapping</tt></a>
<LI><A href="node38.html">5.2 <tt class="module">ZODB.PersistentList</tt></a>
<LI><A href="node39.html">5.3 B-tree Modules</a>
</ul>
<!--End of Table of Child-Links-->
<P>
<DIV CLASS="navigation">
<p><hr>
......@@ -75,7 +77,7 @@ useful data types such as BTrees or full-text indexes.
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<td><A HREF="node37.html"><img src="/python/writing/icons/next.gif"
......@@ -92,11 +94,11 @@ useful data types such as BTrees or full-text indexes.
border="0" height="32"
alt="" width="32"></td>
</tr></table>
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<b class="navlabel">Next:</b> <a class="sectref" HREF="node37.html">5.3 BTrees Package</A>
<hr>
<span class="release-info">Release 0.03, documentation updated on February 8, 2002.</span>
<span class="release-info">Release 0.04, documentation updated on October 4, 2002.</span>
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<title>5.3 BTrees Package</title>
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<td><A HREF="node36.html"><img src="/python/writing/icons/up.gif"
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border="0" height="32"
alt="Up One Level" width="32"></A></td>
<td><A HREF="node38.html"><img src="/python/writing/icons/next.gif"
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border="0" height="32"
alt="" width="32"></td>
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<H2><A NAME="SECTION000610000000000000000">
5.1 <tt class="module">ZODB.PersistentMapping</tt></A>
<H2><A NAME="SECTION000630000000000000000">
5.3 BTrees Package</A>
</H2>
<P>
The <tt class="class">PersistentMapping</tt> class is a wrapper for mapping objects
that will set the dirty bit when the mapping is modified by setting or
deleting a key.
When programming with the ZODB, Python dictionaries aren't always what
you need. The most important case is where you want to store a very
large mapping. When a Python dictionary is accessed in a ZODB, the
whole dictionary has to be unpickled and brought into memory. If
you're storing something very large, such as a 100,000-entry user
database, unpickling such a large object will be slow. BTrees are a
balanced tree data structure that behave like a mapping but distribute
keys throughout a number of tree nodes. The nodes are stored in
sorted order. Nodes are then only unpickled and brought into memory
as they're accessed, so the entire tree doesn't have to occupy memory
(unless you really are touching every single key).
<P>
The BTrees package provides a large collection of related data
structures. There are variants of the data structures specialized to
handle integer values, which are faster and use less memory. There
are four modules that handle the different variants. The first two
letters of the module name specify the types of the keys and values in
mappings - O for any object and I for integer. The
<tt class="module">BTrees.IOBTree</tt> module provides a mapping that accepts integer
keys and arbitrary objects as values.
<P>
The four data structures provide by each module are a btree, a bucket,
a tree set, and a set. The btree and bucket types are mappings and
support all the usual mapping methods, e.g. <tt class="function">update()</tt> and
<tt class="function">keys()</tt>. The tree set and set types are similar to mappings
but they have no values; they support the methods that make sense for
a mapping with no keys, e.g. <tt class="function">keys()</tt> but not
<tt class="function">items()</tt>. The bucket and set types are the individual
building blocks for btrees and tree sets, respectively. A bucket or
set can be used when you are sure that it will have few elements. If
the data structure will grow large, you should use a btree or tree
set.
<P>
The four modules are named <tt class="module">OOBTree</tt>, <tt class="module">IOBTree</tt>,
<tt class="module">OIBTree</tt>, and <tt class="module">IIBTree</tt>. The two letter prefixes are
repeated in the data types names. The <tt class="module">BTrees.OOBTree</tt> module
defines the following types: <tt class="class">OOBTree</tt>, <tt class="class">OOBucket</tt>,
<tt class="class">OOSet</tt>, and <tt class="class">OOTreeSet</tt>.
<P>
<dl><dt><b><a name="l2h-1"><tt class="function">PersistentMapping</tt></a></b>(<var>container = {}</var>)
<dd>
Create a <tt class="class">PersistentMapping</tt> object that wraps the
mapping object <var>container</var>. If you don't specify a
value for <var>container</var>, a regular Python dictionary is used.
</dl>
The <tt class="function">keys()</tt>, <tt class="function">values()</tt>, and <tt class="function">items()</tt>
methods do not materialize a list with all of the data. Instead, they
return lazy sequences that fetch data from the BTree as needed. They
also support optional arguments to specify the minium and maximum
values to return.
<P>
<tt class="class">PersistentMapping</tt> objects support all the same methods as
Python dictionaries do.
A BTree object supports all the methods you would expect of a mapping
with a few extensions that exploit the fact that the keys are sorted.
The example below demonstrates how some of the methods work. The
extra methods re <tt class="function">minKey()</tt> and <tt class="function">maxKey()</tt>, which
find the minimum and maximum key value subject to an optional bound
argument, and <tt class="function">byValue()</tt>, which returns value, key pairs
in reversed sorted order subject to an optional minimum bound argument.
<P>
<div class="verbatim"><pre>
&gt;&gt;&gt; from BTrees.OOBTree import OOBTree
&gt;&gt;&gt; t = OOBTree()
&gt;&gt;&gt; t.update({ 1: "red", 2: "green", 3: "blue", 4: "spades" })
&gt;&gt;&gt; len(t)
4
&gt;&gt;&gt; t[2]
'green'
&gt;&gt;&gt; t.keys()
&lt;OOBTreeItems object at 0x40269098&gt;
&gt;&gt;&gt; [k for k in t.keys()] # use a listcomp to get a printable sequence
[1, 2, 3, 4]
&gt;&gt;&gt; [k for k in t.values()]
['red', 'green', 'blue', 'spades']
&gt;&gt;&gt; [k for k in t.values(1, 2)]
['red', 'green']
&gt;&gt;&gt; [k for k in t.values(2)]
['green', 'blue', 'spades']
&gt;&gt;&gt; t.byValue("glue") # all values &gt; "glue"
[('spades', 4), ('red', 1), ('green', 2)]
&gt;&gt;&gt; t.minKey(1.5)
2
</pre></div>
<P>
Each of the modules also defines some functions that operate on
BTrees - <tt class="function">difference()</tt>, <tt class="function">union()</tt>, and
<tt class="function">difference()</tt>. The <tt class="function">difference()</tt> function returns
a bucket, while the other two methods return a set.
If the keys are integers, then the module also defines
<tt class="function">multiunion()</tt>. If the values are integers, then the module
also defines <tt class="function">weightedIntersection()</tt> and
<tt class="function">weighterUnion()</tt>. The function doc strings describe each
function briefly.
<P>
<P>
......@@ -77,7 +158,7 @@ Python dictionaries do.
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......@@ -94,11 +175,11 @@ Python dictionaries do.
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<span class="release-info">Release 0.04, documentation updated on October 4, 2002.</span>
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<td><A HREF="node36.html"><img src="/python/writing/icons/up.gif"
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......@@ -40,32 +41,45 @@
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<H2><A NAME="SECTION000620000000000000000">
5.2 <tt class="module">ZODB.PersistentList</tt></A>
</H2>
<H1><A NAME="SECTION000700000000000000000">
A. Resources</A>
</H1>
<P>
The <tt class="class">PersistentList</tt> class is a wrapper for mutable sequence objects,
much as <tt class="class">PersistentMapping</tt> is a wrapper for mappings.
ZODB HOWTO, by Michel Pelletier:
<BR>
Goes into slightly more detail about the rules for writing applications using the ZODB.
<BR><a class="url" href="http://www.zope.org/Members/michel/HowTos/ZODB-How-To">http://www.zope.org/Members/michel/HowTos/ZODB-How-To</a>
<P>
Introduction to the Zope Object Database, by Jim Fulton:
<BR>
Goes into much greater detail, explaining advanced uses of the ZODB and
how it's actually implemented. A definitive reference, and highly recommended.
<BR><a class="url" href="http://www.python.org/workshops/2000-01/proceedings/papers/fulton/zodb3.html">http://www.python.org/workshops/2000-01/proceedings/papers/fulton/zodb3.html</a>
<P>
<dl><dt><b><a name="l2h-2"><tt class="function">PersistentList</tt></a></b>(<var>initlist = []</var>)
<dd>
Create a <tt class="class">PersistentList</tt> object that wraps the
mutable sequence object <var>initlist</var>. If you don't specify a
value for <var>initlist</var>, a regular Python list is used.
</dl>
Persistent Programing with ZODB, by Jeremy Hylton and Barry Warsaw:
<BR>
Slides for a tutorial presented at the 10th Python conference. Covers
much of the same ground as this guide, with more details in some areas
and less in others.
<BR><a class="url" href="http://www.zope.org/Members/bwarsaw/ipc10-slides">http://www.zope.org/Members/bwarsaw/ipc10-slides</a>
<P>
Download link for ZEO:
<BR><a class="url" href="http://www.zope.org/Products/ZEO/">http://www.zope.org/Products/ZEO/</a>
<P>
<tt class="class">PersistentList</tt> objects support all the same methods as
Python lists do.
<P>
......@@ -76,7 +90,7 @@ Python lists do.
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<td><A HREF="node39.html"><img src="/python/writing/icons/next.gif"
......@@ -93,11 +107,11 @@ Python lists do.
border="0" height="32"
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<b class="navlabel">Next:</b> <a class="sectref" HREF="node39.html">B. GNU Free Documentation</A>
<hr>
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<span class="release-info">Release 0.04, documentation updated on October 4, 2002.</span>
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border="0" height="32"
alt="Previous Page" width="32"></A></td>
<td><A HREF="node36.html"><img src="/python/writing/icons/up.gif"
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alt="Up One Level" width="32"></A></td>
<td><A HREF="node40.html"><img src="/python/writing/icons/next.gif"
......@@ -39,75 +41,52 @@
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<H2><A NAME="SECTION000630000000000000000">
5.3 B-tree Modules</A>
</H2>
<H1><A NAME="SECTION000800000000000000000">
B. GNU Free Documentation License</A>
</H1>
<P>
When programming with the ZODB, Python dictionaries aren't always what
you need. The most important case is where you want to store a very
large mapping. When a Python dictionary is accessed in a ZODB, the
whole dictionary has to be unpickled and brought into memory. If
you're storing something very large, such as a 100,000-entry user
database, unpickling such a large object will be slow. B-trees are a
balanced tree data structure that behave like a mapping but distribute
keys throughout a number of tree nodes. Nodes are then only unpickled
and brought into memory as they're accessed, so the entire tree
doesn't have to occupy memory (unless you really are touching every
single key).
<P>
There are four different BTree modules provided. One of them, the
<tt class="module">BTree</tt> module, provides the most general data type; the keys
and values in the B-tree can be any Python object. Some specialized B-tree
modules require that the keys, and perhaps even the values, to be of a
certain type, and provide faster performance because of this limitation.
<P>
<DL COMPACT>
<DT> <tt class="module">IOBTree</tt> </DT>
<DD>requires the keys to be integers.
The module name reminds you of this; the <tt class="module">IOBTree</tt> module
maps Integers to Objects.
<P>
</DD>
<DT> <tt class="module">OIBTree</tt> </DT>
<DD>requires the values to be integers,
mapping Objects to Integers.
Version 1.1, March 2000
<BR>
<P>
</DD>
<DT> <tt class="module">IIBTree</tt> </DT>
<DD>is strictest, requiring that both keys and values must be integers.
<P>
</DD>
</DL>
<P>
To use a B-tree, simply import the desired module and call the
constructor, always named <tt class="function">BTree()</tt>, to get a B-tree
instance, and then use it like any other mapping:
<P>
<dl><dd><pre class="verbatim">
import IIBTree
iimap = IIBTree.BTree()
iimap[1972] = 27
</pre></dl>
Copyright <SPAN CLASS="MATH"><IMG
WIDTH="20" HEIGHT="29" ALIGN="MIDDLE" BORDER="0"
SRC="img1.gif"
ALT="$\copyright$"></SPAN> 2000 Free Software Foundation, Inc.
<BR>
59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
<BR>
Everyone is permitted to copy and distribute verbatim copies
of this license document, but changing it is not allowed.
<P>
<p><hr>
<!--Table of Child-Links-->
<A NAME="CHILD_LINKS"><STRONG>Subsections</STRONG></a>
<P>
<UL>
<LI><A href="node40.html">Preamble</a>
<LI><A href="node41.html">B..1 Applicability and Definitions</a>
<LI><A href="node42.html">B..2 Verbatim Copying</a>
<LI><A href="node43.html">B..3 Copying in Quantity</a>
<LI><A href="node44.html">B..4 Modifications</a>
<LI><A href="node45.html">B..5 Combining Documents</a>
<LI><A href="node46.html">B..6 Collections of Documents</a>
<LI><A href="node47.html">B..7 Aggregation With Independent Works</a>
<LI><A href="node48.html">B..8 Translation</a>
<LI><A href="node49.html">B..9 Termination</a>
<LI><A href="node50.html">B..10 Future Revisions of This Licence</a>
<LI><A href="node51.html">ADDENDUM: How to use this License for your documents</a>
</ul>
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<p><hr>
......@@ -116,7 +95,7 @@ iimap[1972] = 27
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<td><A HREF="node40.html"><img src="/python/writing/icons/next.gif"
......@@ -133,11 +112,11 @@ iimap[1972] = 27
border="0" height="32"
alt="" width="32"></td>
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<span class="release-info">Release 0.04, documentation updated on October 4, 2002.</span>
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......@@ -87,7 +88,7 @@ depositing, and 2) how much should be deposited. You might deposit
Mapping these structures to a relational database is straightforward:
<P>
<dl><dd><pre class="verbatim">
<div class="verbatim"><pre>
CREATE TABLE runs (
int run_id,
varchar owner,
......@@ -113,7 +114,7 @@ CREATE TABLE parameters (
FOREIGN KEY(run_id, step_num)
REFERENCES operations(run_id, step_num),
);
</pre></dl>
</pre></div>
<P>
In Python, you would write three classes named <tt class="class">Run</tt>,
......@@ -208,7 +209,7 @@ runs, therefore, is still inefficient, but not grossly inefficient.
<b class="navlabel">Up:</b> <a class="sectref" HREF="node2.html">1 Introduction</A>
<b class="navlabel">Next:</b> <a class="sectref" HREF="node5.html">1.3 What is ZEO?</A>
<hr>
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border="0" height="32"
alt="Previous Page" width="32"></A></td>
<td><A HREF="zodb.html"><img src="/python/writing/icons/up.gif"
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border="0" height="32"
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<H1><A NAME="SECTION000700000000000000000">
A. Resources</A>
</H1>
<H2><A NAME="SECTION000810000000000000000">
Preamble</A>
</H2>
<P>
ZODB HOWTO, by Michel Pelletier:
The purpose of this License is to make a manual, textbook, or other
written document ``free'' in the sense of freedom: to assure everyone
the effective freedom to copy and redistribute it, with or without
modifying it, either commercially or noncommercially. Secondarily,
this License preserves for the author and publisher a way to get
credit for their work, while not being considered responsible for
modifications made by others.
<BR>
Goes into slightly more detail about the rules for writing applications using the ZODB.
<BR><a class="url" href="http://www.zope.org/Members/michel/HowTos/ZODB-How-To">http://www.zope.org/Members/michel/HowTos/ZODB-How-To</a>
<P>
Introduction to the Zope Object Database, by Jim Fulton:
<BR>
Goes into much greater detail, explaining advanced uses of the ZODB and
how it's actually implemented. A definitive reference, and highly recommended.
This License is a kind of ``copyleft'', which means that derivative
works of the document must themselves be free in the same sense. It
complements the GNU General Public License, which is a copyleft
license designed for free software.
<BR><a class="url" href="http://www.python.org/workshops/2000-01/proceedings/papers/fulton/zodb3.html">http://www.python.org/workshops/2000-01/proceedings/papers/fulton/zodb3.html</a>
<P>
Download link for ZEO:
<BR><a class="url" href="http://www.zope.org/Products/ZEO/">http://www.zope.org/Products/ZEO/</a>
<P>
We have designed this License in order to use it for manuals for free
software, because free software needs free documentation: a free
program should come with manuals providing the same freedoms that the
software does. But this License is not limited to software manuals;
it can be used for any textual work, regardless of subject matter or
whether it is published as a printed book. We recommend this License
principally for works whose purpose is instruction or reference.
<P>
......@@ -80,7 +85,7 @@ Download link for ZEO:
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border="0" height="32"
alt="Previous Page" width="32"></A></td>
<td><A HREF="zodb.html"><img src="/python/writing/icons/up.gif"
<td><A HREF="node39.html"><img src="/python/writing/icons/up.gif"
border="0" height="32"
alt="Up One Level" width="32"></A></td>
<td><A HREF="node41.html"><img src="/python/writing/icons/next.gif"
......@@ -97,11 +102,11 @@ Download link for ZEO:
border="0" height="32"
alt="" width="32"></td>
</tr></table>
<b class="navlabel">Previous:</b> <a class="sectref" HREF="node39.html">5.3 B-tree Modules</A>
<b class="navlabel">Up:</b> <a class="sectref" HREF="zodb.html">ZODB/ZEO Programming Guide</A>
<b class="navlabel">Next:</b> <a class="sectref" HREF="node41.html">B. GNU Free Documentation</A>
<b class="navlabel">Previous:</b> <a class="sectref" HREF="node39.html">B. GNU Free Documentation</A>
<b class="navlabel">Up:</b> <a class="sectref" HREF="node39.html">B. GNU Free Documentation</A>
<b class="navlabel">Next:</b> <a class="sectref" HREF="node41.html">B..1 Applicability and Definitions</A>
<hr>
<span class="release-info">Release 0.03, documentation updated on February 8, 2002.</span>
<span class="release-info">Release 0.04, documentation updated on October 4, 2002.</span>
</DIV>
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<html>
<head>
<title>B. GNU Free Documentation License</title>
<META NAME="description" CONTENT="B. GNU Free Documentation License">
<title>B..1 Applicability and Definitions</title>
<META NAME="description" CONTENT="B..1 Applicability and Definitions">
<META NAME="keywords" CONTENT="zodb">
<META NAME="resource-type" CONTENT="document">
<META NAME="distribution" CONTENT="global">
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<meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1">
<link rel="STYLESHEET" href="zodb.css" type='text/css'>
<link rel="first" href="zodb.html">
<link rel="contents" href="contents.html" title="Contents">
<LINK REL="next" href="about.html">
<LINK REL="next" HREF="node42.html">
<LINK REL="previous" HREF="node40.html">
<LINK REL="up" HREF="zodb.html">
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<LINK REL="next" HREF="node42.html">
<meta name='aesop' content='information'>
</head>
<body>
<DIV CLASS="navigation">
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border="0" height="32"
alt="Previous Page" width="32"></A></td>
<td><A HREF="zodb.html"><img src="/python/writing/icons/up.gif"
<td><A HREF="node39.html"><img src="/python/writing/icons/up.gif"
border="0" height="32"
alt="Up One Level" width="32"></A></td>
<td><A HREF="node42.html"><img src="/python/writing/icons/next.gif"
......@@ -40,52 +41,84 @@
border="0" height="32"
alt="" width="32"></td>
</tr></table>
<b class="navlabel">Previous:</b> <a class="sectref" HREF="node40.html">A. Resources</A>
<b class="navlabel">Up:</b> <a class="sectref" HREF="zodb.html">ZODB/ZEO Programming Guide</A>
<b class="navlabel">Next:</b> <a class="sectref" HREF="node42.html">Preamble</A>
<b class="navlabel">Previous:</b> <a class="sectref" HREF="node40.html">Preamble</A>
<b class="navlabel">Up:</b> <a class="sectref" HREF="node39.html">B. GNU Free Documentation</A>
<b class="navlabel">Next:</b> <a class="sectref" HREF="node42.html">B..2 Verbatim Copying</A>
<br><hr>
</DIV>
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<H1><A NAME="SECTION000800000000000000000">
B. GNU Free Documentation License</A>
</H1>
<H2><A NAME="SECTION000820000000000000000">
B..1 Applicability and Definitions</A>
</H2>
<P>
Version 1.1, March 2000
<BR>
This License applies to any manual or other work that contains a
notice placed by the copyright holder saying it can be distributed
under the terms of this License. The ``Document'', below, refers to any
such manual or work. Any member of the public is a licensee, and is
addressed as ``you''.
<P>
Copyright <SPAN CLASS="MATH"><IMG
WIDTH="20" HEIGHT="29" ALIGN="MIDDLE" BORDER="0"
SRC="img1.gif"
ALT="$\copyright$"></SPAN> 2000 Free Software Foundation, Inc.
<BR>
59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
<BR>
Everyone is permitted to copy and distribute verbatim copies
of this license document, but changing it is not allowed.
A ``Modified Version'' of the Document means any work containing the
Document or a portion of it, either copied verbatim, or with
modifications and/or translated into another language.
<P>
A ``Secondary Section'' is a named appendix or a front-matter section of
the Document that deals exclusively with the relationship of the
publishers or authors of the Document to the Document's overall subject
(or to related matters) and contains nothing that could fall directly
within that overall subject. (For example, if the Document is in part a
textbook of mathematics, a Secondary Section may not explain any
mathematics.) The relationship could be a matter of historical
connection with the subject or with related matters, or of legal,
commercial, philosophical, ethical or political position regarding
them.
<p><hr>
<!--Table of Child-Links-->
<A NAME="CHILD_LINKS"><STRONG>Subsections</STRONG></a>
<P>
The ``Invariant Sections'' are certain Secondary Sections whose titles
are designated, as being those of Invariant Sections, in the notice
that says that the Document is released under this License.
<UL>
<LI><A href="node42.html">Preamble</a>
<LI><A href="node43.html">B..1 Applicability and Definitions</a>
<LI><A href="node44.html">B..2 Verbatim Copying</a>
<LI><A href="node45.html">B..3 Copying in Quantity</a>
<LI><A href="node46.html">B..4 Modifications</a>
<LI><A href="node47.html">B..5 Combining Documents</a>
<LI><A href="node48.html">B..6 Collections of Documents</a>
<LI><A href="node49.html">B..7 Aggregation With Independent Works</a>
<LI><A href="node50.html">B..8 Translation</a>
<LI><A href="node51.html">B..9 Termination</a>
<LI><A href="node52.html">B..10 Future Revisions of This Licence</a>
<LI><A href="node53.html">ADDENDUM: How to use this License for your documents</a>
</ul>
<!--End of Table of Child-Links-->
<P>
The ``Cover Texts'' are certain short passages of text that are listed,
as Front-Cover Texts or Back-Cover Texts, in the notice that says that
the Document is released under this License.
<P>
A ``Transparent'' copy of the Document means a machine-readable copy,
represented in a format whose specification is available to the
general public, whose contents can be viewed and edited directly and
straightforwardly with generic text editors or (for images composed of
pixels) generic paint programs or (for drawings) some widely available
drawing editor, and that is suitable for input to text formatters or
for automatic translation to a variety of formats suitable for input
to text formatters. A copy made in an otherwise Transparent file
format whose markup has been designed to thwart or discourage
subsequent modification by readers is not Transparent. A copy that is
not ``Transparent'' is called ``Opaque''.
<P>
Examples of suitable formats for Transparent copies include plain
ASCII without markup, Texinfo input format, <SPAN CLASS="logo,LaTeX">L<SUP><SMALL>A</SMALL></SUP>T<SMALL>E</SMALL>X</SPAN>&nbsp;input format, SGML
or XML using a publicly available DTD, and standard-conforming simple
HTML designed for human modification. Opaque formats include
PostScript, PDF, proprietary formats that can be read and edited only
by proprietary word processors, SGML or XML for which the DTD and/or
processing tools are not generally available, and the
machine-generated HTML produced by some word processors for output
purposes only.
<P>
The ``Title Page'' means, for a printed book, the title page itself,
plus such following pages as are needed to hold, legibly, the material
this License requires to appear in the title page. For works in
formats which do not have any title page as such, ``Title Page'' means
the text near the most prominent appearance of the work's title,
preceding the beginning of the body of the text.
<P>
<DIV CLASS="navigation">
<p><hr>
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<td><A HREF="node40.html"><img src="/python/writing/icons/previous.gif"
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<td><A HREF="zodb.html"><img src="/python/writing/icons/up.gif"
<td><A HREF="node39.html"><img src="/python/writing/icons/up.gif"
border="0" height="32"
alt="Up One Level" width="32"></A></td>
<td><A HREF="node42.html"><img src="/python/writing/icons/next.gif"
......@@ -111,11 +144,11 @@ Everyone is permitted to copy and distribute verbatim copies
border="0" height="32"
alt="" width="32"></td>
</tr></table>
<b class="navlabel">Previous:</b> <a class="sectref" HREF="node40.html">A. Resources</A>
<b class="navlabel">Up:</b> <a class="sectref" HREF="zodb.html">ZODB/ZEO Programming Guide</A>
<b class="navlabel">Next:</b> <a class="sectref" HREF="node42.html">Preamble</A>
<b class="navlabel">Previous:</b> <a class="sectref" HREF="node40.html">Preamble</A>
<b class="navlabel">Up:</b> <a class="sectref" HREF="node39.html">B. GNU Free Documentation</A>
<b class="navlabel">Next:</b> <a class="sectref" HREF="node42.html">B..2 Verbatim Copying</A>
<hr>
<span class="release-info">Release 0.03, documentation updated on February 8, 2002.</span>
<span class="release-info">Release 0.04, documentation updated on October 4, 2002.</span>
</DIV>
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<title>B..2 Verbatim Copying</title>
<META NAME="description" CONTENT="B..2 Verbatim Copying">
<META NAME="keywords" CONTENT="zodb">
<META NAME="resource-type" CONTENT="document">
<META NAME="distribution" CONTENT="global">
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<meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1">
<link rel="STYLESHEET" href="zodb.css" type='text/css'>
<link rel="first" href="zodb.html">
<link rel="contents" href="contents.html" title="Contents">
<LINK REL="next" HREF="node43.html">
<LINK REL="previous" HREF="node41.html">
<LINK REL="up" HREF="node41.html">
<LINK REL="up" HREF="node39.html">
<LINK REL="next" HREF="node43.html">
<meta name='aesop' content='information'>
</head>
<body>
<DIV CLASS="navigation">
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<td><A HREF="node41.html"><img src="/python/writing/icons/previous.gif"
border="0" height="32"
alt="Previous Page" width="32"></A></td>
<td><A HREF="node41.html"><img src="/python/writing/icons/up.gif"
<td><A HREF="node39.html"><img src="/python/writing/icons/up.gif"
border="0" height="32"
alt="Up One Level" width="32"></A></td>
<td><A HREF="node43.html"><img src="/python/writing/icons/next.gif"
......@@ -40,40 +41,31 @@
border="0" height="32"
alt="" width="32"></td>
</tr></table>
<b class="navlabel">Previous:</b> <a class="sectref" HREF="node41.html">B. GNU Free Documentation</A>
<b class="navlabel">Up:</b> <a class="sectref" HREF="node41.html">B. GNU Free Documentation</A>
<b class="navlabel">Next:</b> <a class="sectref" HREF="node43.html">B..1 Applicability and Definitions</A>
<b class="navlabel">Previous:</b> <a class="sectref" HREF="node41.html">B..1 Applicability and Definitions</A>
<b class="navlabel">Up:</b> <a class="sectref" HREF="node39.html">B. GNU Free Documentation</A>
<b class="navlabel">Next:</b> <a class="sectref" HREF="node43.html">B..3 Copying in Quantity</A>
<br><hr>
</DIV>
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<H2><A NAME="SECTION000810000000000000000">
Preamble</A>
<H2><A NAME="SECTION000830000000000000000">
B..2 Verbatim Copying</A>
</H2>
<P>
The purpose of this License is to make a manual, textbook, or other
written document ``free'' in the sense of freedom: to assure everyone
the effective freedom to copy and redistribute it, with or without
modifying it, either commercially or noncommercially. Secondarily,
this License preserves for the author and publisher a way to get
credit for their work, while not being considered responsible for
modifications made by others.
You may copy and distribute the Document in any medium, either
commercially or noncommercially, provided that this License, the
copyright notices, and the license notice saying this License applies
to the Document are reproduced in all copies, and that you add no other
conditions whatsoever to those of this License. You may not use
technical measures to obstruct or control the reading or further
copying of the copies you make or distribute. However, you may accept
compensation in exchange for copies. If you distribute a large enough
number of copies you must also follow the conditions in section 3.
<P>
This License is a kind of ``copyleft'', which means that derivative
works of the document must themselves be free in the same sense. It
complements the GNU General Public License, which is a copyleft
license designed for free software.
<P>
We have designed this License in order to use it for manuals for free
software, because free software needs free documentation: a free
program should come with manuals providing the same freedoms that the
software does. But this License is not limited to software manuals;
it can be used for any textual work, regardless of subject matter or
whether it is published as a printed book. We recommend this License
principally for works whose purpose is instruction or reference.
You may also lend copies, under the same conditions stated above, and
you may publicly display copies.
<P>
......@@ -84,7 +76,7 @@ principally for works whose purpose is instruction or reference.
<td><A HREF="node41.html"><img src="/python/writing/icons/previous.gif"
border="0" height="32"
alt="Previous Page" width="32"></A></td>
<td><A HREF="node41.html"><img src="/python/writing/icons/up.gif"
<td><A HREF="node39.html"><img src="/python/writing/icons/up.gif"
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alt="Up One Level" width="32"></A></td>
<td><A HREF="node43.html"><img src="/python/writing/icons/next.gif"
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border="0" height="32"
alt="" width="32"></td>
</tr></table>
<b class="navlabel">Previous:</b> <a class="sectref" HREF="node41.html">B. GNU Free Documentation</A>
<b class="navlabel">Up:</b> <a class="sectref" HREF="node41.html">B. GNU Free Documentation</A>
<b class="navlabel">Next:</b> <a class="sectref" HREF="node43.html">B..1 Applicability and Definitions</A>
<b class="navlabel">Previous:</b> <a class="sectref" HREF="node41.html">B..1 Applicability and Definitions</A>
<b class="navlabel">Up:</b> <a class="sectref" HREF="node39.html">B. GNU Free Documentation</A>
<b class="navlabel">Next:</b> <a class="sectref" HREF="node43.html">B..3 Copying in Quantity</A>
<hr>
<span class="release-info">Release 0.03, documentation updated on February 8, 2002.</span>
<span class="release-info">Release 0.04, documentation updated on October 4, 2002.</span>
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<html>
<head>
<title>B..6 Collections of Documents</title>
<META NAME="description" CONTENT="B..6 Collections of Documents">
<title>B..8 Translation</title>
<META NAME="description" CONTENT="B..8 Translation">
<META NAME="keywords" CONTENT="zodb">
<META NAME="resource-type" CONTENT="document">
<META NAME="distribution" CONTENT="global">
<meta http-equiv="Content-Type" content="text/html; charset=">
<link rel="STYLESHEET" href="zodb.css">
<meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1">
<link rel="STYLESHEET" href="zodb.css" type='text/css'>
<link rel="first" href="zodb.html">
<link rel="contents" href="contents.html" title="Contents">
<LINK REL="next" HREF="node49.html">
<LINK REL="previous" HREF="node47.html">
<LINK REL="up" HREF="node41.html">
<LINK REL="up" HREF="node39.html">
<LINK REL="next" HREF="node49.html">
<meta name='aesop' content='information'>
</head>
<body>
<DIV CLASS="navigation">
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<td><A HREF="node47.html"><img src="/python/writing/icons/previous.gif"
border="0" height="32"
alt="Previous Page" width="32"></A></td>
<td><A HREF="node41.html"><img src="/python/writing/icons/up.gif"
<td><A HREF="node39.html"><img src="/python/writing/icons/up.gif"
border="0" height="32"
alt="Up One Level" width="32"></A></td>
<td><A HREF="node49.html"><img src="/python/writing/icons/next.gif"
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border="0" height="32"
alt="" width="32"></td>
</tr></table>
<b class="navlabel">Previous:</b> <a class="sectref" HREF="node47.html">B..5 Combining Documents</A>
<b class="navlabel">Up:</b> <a class="sectref" HREF="node41.html">B. GNU Free Documentation</A>
<b class="navlabel">Next:</b> <a class="sectref" HREF="node49.html">B..7 Aggregation With Independent</A>
<b class="navlabel">Previous:</b> <a class="sectref" HREF="node47.html">B..7 Aggregation With Independent</A>
<b class="navlabel">Up:</b> <a class="sectref" HREF="node39.html">B. GNU Free Documentation</A>
<b class="navlabel">Next:</b> <a class="sectref" HREF="node49.html">B..9 Termination</A>
<br><hr>
</DIV>
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<H2><A NAME="SECTION000870000000000000000">
B..6 Collections of Documents</A>
<H2><A NAME="SECTION000890000000000000000">
B..8 Translation</A>
</H2>
<P>
You may make a collection consisting of the Document and other documents
released under this License, and replace the individual copies of this
License in the various documents with a single copy that is included in
the collection, provided that you follow the rules of this License for
verbatim copying of each of the documents in all other respects.
<P>
You may extract a single document from such a collection, and distribute
it individually under this License, provided you insert a copy of this
License into the extracted document, and follow this License in all
other respects regarding verbatim copying of that document.
Translation is considered a kind of modification, so you may
distribute translations of the Document under the terms of section 4.
Replacing Invariant Sections with translations requires special
permission from their copyright holders, but you may include
translations of some or all Invariant Sections in addition to the
original versions of these Invariant Sections. You may include a
translation of this License provided that you also include the
original English version of this License. In case of a disagreement
between the translation and the original English version of this
License, the original English version will prevail.
<P>
......@@ -73,7 +73,7 @@ other respects regarding verbatim copying of that document.
<td><A HREF="node47.html"><img src="/python/writing/icons/previous.gif"
border="0" height="32"
alt="Previous Page" width="32"></A></td>
<td><A HREF="node41.html"><img src="/python/writing/icons/up.gif"
<td><A HREF="node39.html"><img src="/python/writing/icons/up.gif"
border="0" height="32"
alt="Up One Level" width="32"></A></td>
<td><A HREF="node49.html"><img src="/python/writing/icons/next.gif"
......@@ -90,11 +90,11 @@ other respects regarding verbatim copying of that document.
border="0" height="32"
alt="" width="32"></td>
</tr></table>
<b class="navlabel">Previous:</b> <a class="sectref" HREF="node47.html">B..5 Combining Documents</A>
<b class="navlabel">Up:</b> <a class="sectref" HREF="node41.html">B. GNU Free Documentation</A>
<b class="navlabel">Next:</b> <a class="sectref" HREF="node49.html">B..7 Aggregation With Independent</A>
<b class="navlabel">Previous:</b> <a class="sectref" HREF="node47.html">B..7 Aggregation With Independent</A>
<b class="navlabel">Up:</b> <a class="sectref" HREF="node39.html">B. GNU Free Documentation</A>
<b class="navlabel">Next:</b> <a class="sectref" HREF="node49.html">B..9 Termination</A>
<hr>
<span class="release-info">Release 0.03, documentation updated on February 8, 2002.</span>
<span class="release-info">Release 0.04, documentation updated on October 4, 2002.</span>
</DIV>
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"""Internal helper to reset the logging label (e.g. after fork())."""
global _label
_label = "ZSS:%s" % os.getpid()
def log(message, level=zLOG.INFO, label=None, error=None):
"""Internal helper to log a message using zLOG."""
zLOG.LOG(label or _label, level, message, error=error)
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