tdb2: update design doc.

ccan/tdb2/doc/design.lyx

@@ -53,8 +53,8 @@ Rusty Russell, IBM Corporation
 
 \change_deleted 0 1283307542
 26-July
-\change_inserted 0 1284016854
-9-September
+\change_inserted 0 1284423485
+14-September
 \change_unchanged
 -2010
 \end_layout
@@ -476,6 +476,17 @@ The tdb_open() call was expanded to tdb_open_ex(), which added an optional
 
 \begin_layout Subsubsection
 Proposed Solution
+\change_inserted 0 1284422789
+
+\begin_inset CommandInset label
+LatexCommand label
+name "attributes"
+
+\end_inset
+
+
+\change_unchanged
+
 \end_layout
 
 \begin_layout Standard
@@ -1289,13 +1300,69 @@ Proposed Solution
 
 \begin_layout Standard
 
-\change_inserted 0 1284016847
+\change_inserted 0 1284422552
 We often have extra padding at the tail of a record.
  If we ensure that the first byte (if any) of this padding is zero, we will
  have a way for future changes to detect code which doesn't understand a
  new format: the new code would write (say) a 1 at the tail, and thus if
  there is no tail or the first byte is 0, we would know the extension is
  not present on that record.
+\end_layout
+
+\begin_layout Subsection
+
+\change_inserted 0 1284422568
+TDB Does Not Use Talloc
+\end_layout
+
+\begin_layout Standard
+
+\change_inserted 0 1284422646
+Many users of TDB (particularly Samba) use the talloc allocator, and thus
+ have to wrap TDB in a talloc context to use it conveniently.
+\end_layout
+
+\begin_layout Subsubsection
+
+\change_inserted 0 1284422656
+Proposed Solution
+\end_layout
+
+\begin_layout Standard
+
+\change_inserted 0 1284423065
+The allocation within TDB is not complicated enough to justify the use of
+ talloc, and I am reluctant to force another (excellent) library on TDB
+ users.
+ Nonetheless a compromise is possible.
+ An attribute (see 
+\begin_inset CommandInset ref
+LatexCommand ref
+reference "attributes"
+
+\end_inset
+
+) can be added later to tdb_open() to provide an alternate allocation mechanism,
+ specifically for talloc but usable by any other allocator (which would
+ ignore the 
+\begin_inset Quotes eld
+\end_inset
+
+context
+\begin_inset Quotes erd
+\end_inset
+
+ argument).
+\end_layout
+
+\begin_layout Standard
+
+\change_inserted 0 1284423042
+This would form a talloc heirarchy as expected, but the caller would still
+ have to attach a destructor to the tdb context returned from tdb_open to
+ close it.
+ All TDB_DATA fields would be children of the tdb_context, and the caller
+ would still have to manage them (using talloc_free() or talloc_steal()).
 \change_unchanged
 
 \end_layout
@@ -1875,7 +1942,7 @@ status open
 
 \begin_layout Plain Layout
 
-\change_inserted 0 1283310945
+\change_inserted 0 1284424151
 Using 
 \begin_inset Formula $2^{16+N*3}$
 \end_inset
@@ -1886,6 +1953,8 @@ means 0 gives a minimal 65536-byte zone, 15 gives the maximal
 
  byte zone.
  Zones range in factor of 8 steps.
+ Given the zone size for the zone the current record is in, we can determine
+ the start of the zone.
 \change_unchanged
 
 \end_layout
@@ -2330,6 +2399,8 @@ TDB Does Not Have Snapshot Support
 
 \begin_layout Subsubsection
 Proposed Solution
+\change_deleted 0 1284423472
+
 \end_layout
 
 \begin_layout Standard
@@ -2342,7 +2413,23 @@ use a real database
 \begin_inset Quotes erd
 \end_inset
 
+
+\change_inserted 0 1284423891
+ 
+\change_deleted 0 1284423891
 .
+
+\change_inserted 0 1284423901
+ (but see 
+\begin_inset CommandInset ref
+LatexCommand ref
+reference "replay-attribute"
+
+\end_inset
+
+).
+\change_unchanged
+
 \end_layout
 
 \begin_layout Standard
@@ -2365,6 +2452,8 @@ This would not allow arbitrary changes to the database, such as tdb_repack
 \begin_layout Standard
 We could then implement snapshots using a similar method, using multiple
  different hash tables/free tables.
+\change_inserted 0 1284423495
+
 \end_layout
 
 \begin_layout Subsection
@@ -2384,6 +2473,18 @@ Proposed Solution
 \end_layout
 
 \begin_layout Standard
+
+\change_inserted 0 1284424201
+None (but see 
+\begin_inset CommandInset ref
+LatexCommand ref
+reference "replay-attribute"
+
+\end_inset
+
+).
+ 
+\change_unchanged
 We could solve a small part of the problem by providing read-only transactions.
  These would allow one write transaction to begin, but it could not commit
  until all r/o transactions are done.
@@ -2569,6 +2670,53 @@ At some later point, a sync would allow recovery of the old data into the
  free lists (perhaps when the array of top-level pointers filled).
  On crash, tdb_open() would examine the array of top levels, and apply the
  transactions until it encountered an invalid checksum.
+\change_inserted 0 1284423555
+
+\end_layout
+
+\begin_layout Subsection
+
+\change_inserted 0 1284423617
+Tracing Is Fragile, Replay Is External
+\end_layout
+
+\begin_layout Standard
+
+\change_inserted 0 1284423719
+The current TDB has compile-time-enabled tracing code, but it often breaks
+ as it is not enabled by default.
+ In a similar way, the ctdb code has an external wrapper which does replay
+ tracing so it can coordinate cluster-wide transactions.
+\end_layout
+
+\begin_layout Subsubsection
+
+\change_inserted 0 1284423864
+Proposed Solution
+\begin_inset CommandInset label
+LatexCommand label
+name "replay-attribute"
+
+\end_inset
+
+
+\end_layout
+
+\begin_layout Standard
+
+\change_inserted 0 1284423850
+Tridge points out that an attribute can be later added to tdb_open (see
+ 
+\begin_inset CommandInset ref
+LatexCommand ref
+reference "attributes"
+
+\end_inset
+
+) to provide replay/trace hooks, which could become the basis for this and
+ future parallel transactions and snapshot support.
+\change_unchanged
+
 \end_layout
 
 \end_body

ccan/tdb2/doc/design.lyx,v

-head	1.9;
+head	1.10;
 access;
 symbols;
 locks; strict;
 comment	@# @;
 
 
+1.10
+date	2010.09.14.00.33.57;	author rusty;	state Exp;
+branches;
+next	1.9;
+
 1.9
 date	2010.09.09.07.25.12;	author rusty;	state Exp;
 branches;
@@ -56,9 +61,9 @@ desc
 @
 
 
-1.9
+1.10
 log
-@Extension mechanism.
+@Tracing attribute, talloc support.
 @
 text
 @#LyX 1.6.5 created this file. For more info see http://www.lyx.org/
@@ -116,8 +121,8 @@ Rusty Russell, IBM Corporation
 
 \change_deleted 0 1283307542
 26-July
-\change_inserted 0 1284016854
-9-September
+\change_inserted 0 1284423485
+14-September
 \change_unchanged
 -2010
 \end_layout
@@ -539,6 +544,17 @@ The tdb_open() call was expanded to tdb_open_ex(), which added an optional
 
 \begin_layout Subsubsection
 Proposed Solution
+\change_inserted 0 1284422789
+
+\begin_inset CommandInset label
+LatexCommand label
+name "attributes"
+
+\end_inset
+
+
+\change_unchanged
+
 \end_layout
 
 \begin_layout Standard
@@ -1352,13 +1368,69 @@ Proposed Solution
 
 \begin_layout Standard
 
-\change_inserted 0 1284016847
+\change_inserted 0 1284422552
 We often have extra padding at the tail of a record.
  If we ensure that the first byte (if any) of this padding is zero, we will
  have a way for future changes to detect code which doesn't understand a
  new format: the new code would write (say) a 1 at the tail, and thus if
  there is no tail or the first byte is 0, we would know the extension is
  not present on that record.
+\end_layout
+
+\begin_layout Subsection
+
+\change_inserted 0 1284422568
+TDB Does Not Use Talloc
+\end_layout
+
+\begin_layout Standard
+
+\change_inserted 0 1284422646
+Many users of TDB (particularly Samba) use the talloc allocator, and thus
+ have to wrap TDB in a talloc context to use it conveniently.
+\end_layout
+
+\begin_layout Subsubsection
+
+\change_inserted 0 1284422656
+Proposed Solution
+\end_layout
+
+\begin_layout Standard
+
+\change_inserted 0 1284423065
+The allocation within TDB is not complicated enough to justify the use of
+ talloc, and I am reluctant to force another (excellent) library on TDB
+ users.
+ Nonetheless a compromise is possible.
+ An attribute (see 
+\begin_inset CommandInset ref
+LatexCommand ref
+reference "attributes"
+
+\end_inset
+
+) can be added later to tdb_open() to provide an alternate allocation mechanism,
+ specifically for talloc but usable by any other allocator (which would
+ ignore the 
+\begin_inset Quotes eld
+\end_inset
+
+context
+\begin_inset Quotes erd
+\end_inset
+
+ argument).
+\end_layout
+
+\begin_layout Standard
+
+\change_inserted 0 1284423042
+This would form a talloc heirarchy as expected, but the caller would still
+ have to attach a destructor to the tdb context returned from tdb_open to
+ close it.
+ All TDB_DATA fields would be children of the tdb_context, and the caller
+ would still have to manage them (using talloc_free() or talloc_steal()).
 \change_unchanged
 
 \end_layout
@@ -1938,7 +2010,7 @@ status open
 
 \begin_layout Plain Layout
 
-\change_inserted 0 1283310945
+\change_inserted 0 1284424151
 Using 
 \begin_inset Formula $2^{16+N*3}$
 \end_inset
@@ -1949,6 +2021,8 @@ means 0 gives a minimal 65536-byte zone, 15 gives the maximal
 
  byte zone.
  Zones range in factor of 8 steps.
+ Given the zone size for the zone the current record is in, we can determine
+ the start of the zone.
 \change_unchanged
 
 \end_layout
@@ -2393,6 +2467,8 @@ TDB Does Not Have Snapshot Support
 
 \begin_layout Subsubsection
 Proposed Solution
+\change_deleted 0 1284423472
+
 \end_layout
 
 \begin_layout Standard
@@ -2405,7 +2481,23 @@ use a real database
 \begin_inset Quotes erd
 \end_inset
 
+
+\change_inserted 0 1284423891
+ 
+\change_deleted 0 1284423891
 .
+
+\change_inserted 0 1284423901
+ (but see 
+\begin_inset CommandInset ref
+LatexCommand ref
+reference "replay-attribute"
+
+\end_inset
+
+).
+\change_unchanged
+
 \end_layout
 
 \begin_layout Standard
@@ -2428,6 +2520,8 @@ This would not allow arbitrary changes to the database, such as tdb_repack
 \begin_layout Standard
 We could then implement snapshots using a similar method, using multiple
  different hash tables/free tables.
+\change_inserted 0 1284423495
+
 \end_layout
 
 \begin_layout Subsection
@@ -2447,6 +2541,18 @@ Proposed Solution
 \end_layout
 
 \begin_layout Standard
+
+\change_inserted 0 1284424201
+None (but see 
+\begin_inset CommandInset ref
+LatexCommand ref
+reference "replay-attribute"
+
+\end_inset
+
+).
+ 
+\change_unchanged
 We could solve a small part of the problem by providing read-only transactions.
  These would allow one write transaction to begin, but it could not commit
  until all r/o transactions are done.
@@ -2632,6 +2738,53 @@ At some later point, a sync would allow recovery of the old data into the
  free lists (perhaps when the array of top-level pointers filled).
  On crash, tdb_open() would examine the array of top levels, and apply the
  transactions until it encountered an invalid checksum.
+\change_inserted 0 1284423555
+
+\end_layout
+
+\begin_layout Subsection
+
+\change_inserted 0 1284423617
+Tracing Is Fragile, Replay Is External
+\end_layout
+
+\begin_layout Standard
+
+\change_inserted 0 1284423719
+The current TDB has compile-time-enabled tracing code, but it often breaks
+ as it is not enabled by default.
+ In a similar way, the ctdb code has an external wrapper which does replay
+ tracing so it can coordinate cluster-wide transactions.
+\end_layout
+
+\begin_layout Subsubsection
+
+\change_inserted 0 1284423864
+Proposed Solution
+\begin_inset CommandInset label
+LatexCommand label
+name "replay-attribute"
+
+\end_inset
+
+
+\end_layout
+
+\begin_layout Standard
+
+\change_inserted 0 1284423850
+Tridge points out that an attribute can be later added to tdb_open (see
+ 
+\begin_inset CommandInset ref
+LatexCommand ref
+reference "attributes"
+
+\end_inset
+
+) to provide replay/trace hooks, which could become the basis for this and
+ future parallel transactions and snapshot support.
+\change_unchanged
+
 \end_layout
 
 \end_body
@@ -2639,6 +2792,33 @@ At some later point, a sync would allow recovery of the old data into the
 @
 
 
+1.9
+log
+@Extension mechanism.
+@
+text
+@d56 2
+a57 2
+\change_inserted 0 1284016854
+9-September
+d479 11
+d1303 1
+a1303 1
+\change_inserted 0 1284016847
+d1310 56
+d1945 1
+a1945 1
+\change_inserted 0 1283310945
+d1956 2
+d2402 2
+d2416 4
+d2421 12
+d2455 2
+d2476 12
+d2673 47
+@
+
+
 1.8
 log
 @Remove bogus footnote

ccan/tdb2/doc/design.txt

@@ -2,7 +2,7 @@ TDB2: A Redesigning The Trivial DataBase
 
 Rusty Russell, IBM Corporation
 
-9-September-2010
+14-September-2010
 
 Abstract
 
@@ -74,7 +74,7 @@ optional hashing function and an optional logging function
 argument. Additional arguments to open would require the 
 introduction of a tdb_open_ex2 call etc.
 
-2.1.1 Proposed Solution
+2.1.1 Proposed Solution<attributes>
 
 tdb_open() will take a linked-list of attributes:
 
@@ -519,6 +519,28 @@ understand a new format: the new code would write (say) a 1 at
 the tail, and thus if there is no tail or the first byte is 0, we 
 would know the extension is not present on that record.
 
+2.17 TDB Does Not Use Talloc
+
+Many users of TDB (particularly Samba) use the talloc allocator, 
+and thus have to wrap TDB in a talloc context to use it 
+conveniently.
+
+2.17.1 Proposed Solution
+
+The allocation within TDB is not complicated enough to justify 
+the use of talloc, and I am reluctant to force another 
+(excellent) library on TDB users. Nonetheless a compromise is 
+possible. An attribute (see [attributes]) can be added later to 
+tdb_open() to provide an alternate allocation mechanism, 
+specifically for talloc but usable by any other allocator (which 
+would ignore the “context” argument).
+
+This would form a talloc heirarchy as expected, but the caller 
+would still have to attach a destructor to the tdb context 
+returned from tdb_open to close it. All TDB_DATA fields would be 
+children of the tdb_context, and the caller would still have to 
+manage them (using talloc_free() or talloc_steal()).
+
 3 Performance And Scalability Issues
 
 3.1 <TDB_CLEAR_IF_FIRST-Imposes-Performance>TDB_CLEAR_IF_FIRST 
@@ -790,7 +812,9 @@ question “what zone is this record in?” much harder (and “pick a
 random zone”, but that's less common). It could be done with as 
 few as 4 bits from the record header.[footnote:
 Using 2^{16+N*3}means 0 gives a minimal 65536-byte zone, 15 gives 
-the maximal 2^{61} byte zone. Zones range in factor of 8 steps.
+the maximal 2^{61} byte zone. Zones range in factor of 8 steps. 
+Given the zone size for the zone the current record is in, we can 
+determine the start of the zone.
 ]
 
 3.6 <sub:TDB-Becomes-Fragmented>TDB Becomes Fragmented
@@ -1009,7 +1033,8 @@ we need only check for recovery if this is set.
 
 3.9.1 Proposed Solution
 
-None. At some point you say “use a real database”.
+None. At some point you say “use a real database”  (but see [replay-attribute]
+).
 
 But as a thought experiment, if we implemented transactions to 
 only overwrite free entries (this is tricky: there must not be a 
@@ -1038,11 +1063,11 @@ failed.
 
 3.10.1 Proposed Solution
 
-We could solve a small part of the problem by providing read-only 
-transactions. These would allow one write transaction to begin, 
-but it could not commit until all r/o transactions are done. This 
-would require a new RO_TRANSACTION_LOCK, which would be upgraded 
-on commit.
+None (but see [replay-attribute]). We could solve a small part of 
+the problem by providing read-only transactions. These would 
+allow one write transaction to begin, but it could not commit 
+until all r/o transactions are done. This would require a new 
+RO_TRANSACTION_LOCK, which would be upgraded on commit.
 
 3.11 Default Hash Function Is Suboptimal
 
@@ -1137,3 +1162,17 @@ filled). On crash, tdb_open() would examine the array of top
 levels, and apply the transactions until it encountered an 
 invalid checksum.
 
+3.15 Tracing Is Fragile, Replay Is External
+
+The current TDB has compile-time-enabled tracing code, but it 
+often breaks as it is not enabled by default. In a similar way, 
+the ctdb code has an external wrapper which does replay tracing 
+so it can coordinate cluster-wide transactions.
+
+3.15.1 Proposed Solution<replay-attribute>
+
+Tridge points out that an attribute can be later added to 
+tdb_open (see [attributes]) to provide replay/trace hooks, which 
+could become the basis for this and future parallel transactions 
+and snapshot support.
+