Add a tool to print out the last n transactions in a storage.

Add fstools module with simple utilities for jumping around in a Data.fs.

src/ZODB/fstools.py

+##############################################################################
+#
+# Copyright (c) 2001, 2002 Zope Corporation and Contributors.
+# All Rights Reserved.
+#
+# This software is subject to the provisions of the Zope Public License,
+# Version 2.0 (ZPL).  A copy of the ZPL should accompany this distribution.
+# THIS SOFTWARE IS PROVIDED "AS IS" AND ANY AND ALL EXPRESS OR IMPLIED
+# WARRANTIES ARE DISCLAIMED, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
+# WARRANTIES OF TITLE, MERCHANTABILITY, AGAINST INFRINGEMENT, AND FITNESS
+# FOR A PARTICULAR PURPOSE
+#
+##############################################################################
+
+"""Tools for using FileStorage data files.
+
+XXX This module needs tests.
+XXX This file needs to be kept in sync with FileStorage.py.
+"""
+
+import cPickle
+import struct
+
+from ZODB.FileStorage import TRANS_HDR, DATA_HDR, TRANS_HDR_LEN, \
+     DATA_HDR_LEN, DATA_VERSION_HDR_LEN
+from ZODB.utils import p64, u64
+from ZODB.TimeStamp import TimeStamp
+
+class TxnHeader:
+    """Object representing a transaction record header.
+
+    Attribute   Position  Value
+    ---------   --------  -----
+    tid           0- 8    transaction id
+    length        8-16    length of entire transaction record - 8
+    status       16-17    status of transaction (' ', 'u', 'p'?)
+    user_len     17-19    length of user field (pack code H)
+    descr_len    19-21    length of description field (pack code H)
+    ext_len      21-23    length of extensions (pack code H)
+    """
+
+    def __init__(self, file, pos):
+        self._file = file
+        self._pos = pos
+        self._read_header()
+
+    def _read_header(self):
+        self._file.seek(self._pos)
+        self._hdr = self._file.read(TRANS_HDR_LEN)
+        (self.tid, length, self.status, self.user_len, self.descr_len,
+         self.ext_len) = struct.unpack(TRANS_HDR, self._hdr)
+        self.length = u64(length)
+
+    def read_meta(self):
+        """Load user, descr, and ext attributes."""
+        self.user = ""
+        self.descr = ""
+        self.ext = {}
+        if not (self.user_len or self.descr_len or self.ext_len):
+            return
+        self._file.seek(self._pos + TRANS_HDR_LEN)
+        if self.user_len:
+            self.user = self._file.read(self.user_len)
+        if self.descr_len:
+            self.descr = self._file.read(self.descr_len)
+        if self.ext_len:
+            self._ext = self._file.read(self.ext_len)
+            self.ext = cPickle.loads(self._ext)
+
+    def get_data_offset(self):
+        return (self._pos + TRANS_HDR_LEN + self.user_len + self.descr_len
+                + self.ext_len)
+
+    def get_timestamp(self):
+        return TimeStamp(self.tid)
+
+    def get_raw_data(self):
+        data_off = self.get_data_offset()
+        data_len = self.length - (data_off - self._pos)
+        self._file.seek(data_off)
+        return self._file.read(data_len)
+
+    def next_txn(self):
+        off = self._pos + self.length + 8
+        self._file.seek(off)
+        s = self._file.read(8)
+        if not s:
+            return None
+        return TxnHeader(self._file, off)
+
+    def prev_txn(self):
+        if self._pos == 4:
+            return None
+        self._file.seek(self._pos - 8)
+        tlen = u64(self._file.read(8))
+        return TxnHeader(self._file, self._pos - (tlen + 8))
+
+class DataHeader:
+    """Object representing a data record header.
+
+    Attribute         Position  Value
+    ---------         --------  -----
+    oid                 0- 8    object id
+    serial              8-16    object serial numver
+    prev_rec_pos       16-24    position of previous data record for object
+    txn_pos            24-32    position of txn header
+    version_len        32-34    length of version
+    data_len           34-42    length of data
+    nonversion_pos     42-50*   position of nonversion data record
+    prev_version_pos   50-58*   pos of previous version data record
+
+    * these attributes are only present if version_len != 0.
+    """
+
+    def __init__(self, file, pos):
+        self._file = file
+        self._pos = pos
+        self._read_header()
+
+    def _read_header(self):
+        self._file.seek(self._pos)
+        self._hdr = self._file.read(DATA_VERSION_HDR_LEN)
+        # always read the longer header, just in case
+        (self.oid, self.serial, prev_rec_pos, txn_pos, self.version_len,
+         data_len) = struct.unpack(DATA_HDR, self._hdr[:DATA_HDR_LEN])
+        self.prev_rec_pos = u64(prev_rec_pos)
+        self.txn_pos = u64(txn_pos)
+        self.data_len = u64(data_len)
+        if self.version_len:
+            s = self._hdr[DATA_HDR_LEN:]
+            self.nonversion_pos = u64(s[:8])
+            self.prev_version_pos = u64(s[8:])
+        else:
+            self.nonversion_pos = None
+            self.prev_version_pos = None
+
+    def next_offset(self):
+        """Return offset of next record."""
+        off = self._pos + self.data_len
+        if self.version_len:
+            off += self.version_len + DATA_VERSION_HDR_LEN
+        else:
+            off += DATA_HDR_LEN
+        if self.data_len == 0:
+            off += 8 # backpointer
+        return off
+
+def prev_txn(f):
+    """Return transaction located before current file position."""
+    f.seek(-8, 1)
+    tlen = u64(f.read(8)) + 8
+    return TxnHeader(f, f.tell() - tlen)

src/scripts/fstail.py

+#! /usr/bin/env python
+##############################################################################
+#
+# Copyright (c) 2001, 2002 Zope Corporation and Contributors.
+# All Rights Reserved.
+#
+# This software is subject to the provisions of the Zope Public License,
+# Version 2.0 (ZPL).  A copy of the ZPL should accompany this distribution.
+# THIS SOFTWARE IS PROVIDED "AS IS" AND ANY AND ALL EXPRESS OR IMPLIED
+# WARRANTIES ARE DISCLAIMED, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
+# WARRANTIES OF TITLE, MERCHANTABILITY, AGAINST INFRINGEMENT, AND FITNESS
+# FOR A PARTICULAR PURPOSE
+#
+##############################################################################
+"""Tool to dump the last few transactions from a FileStorage."""
+
+from ZODB.fstools import prev_txn, TxnHeader
+
+import binascii
+import getopt
+import sha
+import sys
+
+def main(path, ntxn):
+    f = open(path, "rb")
+    f.seek(0, 2)
+    th = prev_txn(f)
+    i = ntxn
+    while th and i > 0:
+        hash = sha.sha(th.get_raw_data()).digest()
+        l = len(str(th.get_timestamp())) + 1
+        th.read_meta()
+        print "%s: hash=%s" % (th.get_timestamp(),
+                               binascii.hexlify(hash))
+        print " " * l, ("user=%r description=%r length=%d"
+                        % (th.user, th.descr, th.length))
+        th = th.prev_txn()
+        i -= 1
+
+if __name__ == "__main__":
+    ntxn = 10
+    opts, args = getopt.getopt(sys.argv[1:], "n:")
+    path, = args
+    for k, v in opts:
+        if k == '-n':
+            ntxn = int(v)
+    main(path, ntxn)