[Zope-Checkins] CVS: StandaloneZODB/ZODB - FileStorage.py:1.89
Jeremy Hylton
jeremy@zope.com
Sat, 30 Mar 2002 01:05:09 -0500
Update of /cvs-repository/StandaloneZODB/ZODB
In directory cvs.zope.org:/tmp/cvs-serv12308
Modified Files:
FileStorage.py
Log Message:
Simplify transactional undo implementation.
Use the file position stored in the transaction_id whenever possible.
It is possible when _check_txn_pos() returns true; i.e. when the file
position does point to the transaction record header.
Remove ostloc and here arguments to _txn_undo_write(), as they can be
computed after the call.
Omit redundant tests in _txn_undo_write(). All the paths that lead
here verify that the file position is valid.
Remove some attribute lookup optimizations.
=== StandaloneZODB/ZODB/FileStorage.py 1.88 => 1.89 ===
'Undo is currently disabled for database maintenance.<p>')
pos = self._pos
- # BAW: Why 39 please? This makes no sense (see also below).
- if pos < 39:
- return []
- file=self._file
- seek=file.seek
- read=file.read
r = []
i = 0
+ # BAW: Why 39 please? This makes no sense (see also below).
while i < last and pos > 39:
self._file.seek(pos - 8)
pos = pos - U64(self._file.read(8)) - 8
@@ -1097,7 +1092,7 @@
e = loads(read(el))
except:
pass
- next = read(8)
+ next = self._file.read(8)
# next is either the redundant txn length - 8, or an oid
if next == tl:
# There were no objects in this txn
@@ -1136,64 +1131,72 @@
self._lock_acquire()
try:
- return self._transactional_undo(transaction_id)
+ return self._txn_undo(transaction_id)
finally:
self._lock_release()
- def _transactional_undo(self, transaction_id):
- # As seen in undoLog() below, transaction_id encodes the tid and
- # possibly the oid of the first object in the transaction record.
- # transaction_id will be of length 16 if there were objects
- # affected by the txn, and 8 if there weren't (e.g. abortVersion()
- # and commitVersion()). In the latter case, we could still find
- # the transaction through an expensive search of the file, but
- # we're punting on that for now.
+ def _txn_undo(self, transaction_id):
+ # Find the right transaction to undo and call _txn_undo_write().
transaction_id = base64.decodestring(transaction_id + '\n')
tid = transaction_id[:8]
- pos = U64(transaction_id[8:16])
- # XXX
- oid = transaction_id[16:]
- if oid == '' or not self._index.has_key(oid):
- # We can't get the position of the transaction easily.
- # Note that there is a position encoded in the
- # transaction_id at [8:16], but it can't be used reliably
- # across multiple file storages and thus breaks
- # transactional integrity.
- raise UndoError, 'Undoing a non-object affecting transaction'
- # Find the file position for the current revision of this object,
- # and search back for the beginning of its transaction record
- pos = self._index[oid]
- ostloc = p64(self._pos)
- here = self._pos + (self._tfile.tell() + self._thl)
- while 1:
- self._file.seek(pos)
- h = self._file.read(DATA_HDR_LEN)
- doid, serial, prev, tpos, vlen, plen = \
- unpack('>8s8s8s8sH8s', h)
- tpos = U64(tpos)
- self._file.seek(tpos)
- # Read transaction id to see if we've got a match
- thistid = self._file.read(8)
- if thistid == tid:
- break # Yeee ha!
- # Keep looking
- pos = U64(prev)
- if not pos:
- # We never found the right transaction
- raise UndoError('Invalid undo transaction id')
- # We're sitting at the transaction we want to undo, but let's move
- # the file pointer back to the start of the txn record.
- tindex = self._txn_undo_write(tpos, tid, ostloc, here)
+ tpos = U64(transaction_id[8:16])
+ if not self._check_txn_pos(tpos, tid):
+ # If the pos and tid don't match, we must use the oid to
+ # find the transaction record. Find the file position for
+ # the current revision of this object, and search back for
+ # the beginning of its transaction record
+ oid = transaction_id[16:]
+ if oid == '' or not self._index.has_key(oid):
+ # XXX Is this the right error message?
+ raise UndoError('Undoing a non-object affecting transaction')
+ pos = self._index[oid]
+ while 1:
+ self._file.seek(pos)
+ h = self._file.read(DATA_HDR_LEN)
+ doid, serial, prev, tpos, vlen, plen = \
+ unpack('>8s8s8s8sH8s', h)
+ tpos = U64(tpos)
+ self._file.seek(tpos)
+ # Read transaction id to see if we've got a match
+ thistid = self._file.read(8)
+ if thistid == tid:
+ break # Yeee ha!
+ # Keep looking
+ pos = U64(prev)
+ if not pos:
+ # We never found the right transaction
+ raise UndoError('Invalid undo transaction id')
+ tindex = self._txn_undo_write(tpos, tid)
self._tindex.update(tindex)
return tindex.keys()
- def _txn_undo_write(self, tpos, tid, ostloc, here):
+ def _check_txn_pos(self, pos, tid):
+ "Return true if pos is location of the transaction record for tid."
+ self._file.seek(pos)
+ this_tid = self._file.read(8)
+ if this_tid != tid:
+ return 0
+ # be extra cautious: Check the record length makes sense, to
+ # guard against a random file location that happens to have
+ # the right 8-byte pattern.
+ stlen = self._file.read(8)
+ tlen = U64(stlen)
+ self._file.seek(tlen, 1)
+ redundant_stlen = self._file.read(8)
+ if len(redundant_stlen) != 8:
+ return 0
+ if redundant_stlen != stlen:
+ return 0
+ return 1
+
+ def _txn_undo_write(self, tpos, tid):
# a helper function to write the data records for transactional undo
+
+ ostloc = p64(self._pos)
+ here = self._pos + (self._tfile.tell() + self._thl)
+ # Let's move the file pointer back to the start of the txn record.
self._file.seek(tpos)
h = self._file.read(TRANS_HDR_LEN)
- # XXX jer: don't think the second test is needed at this point
- if len(h) != TRANS_HDR_LEN or h[:8] != tid:
- raise UndoError('Invalid undo transaction id')
if h[16] == 'u':
return
if h[16] != ' ':
@@ -1230,7 +1233,7 @@
# Don't fail right away. We may be redeemed later!
failures[oid] = v
else:
- plen =len(p)
+ plen = len(p)
self._tfile.write(pack(">8s8s8s8sH8s",
oid, self._serial, p64(ipos),
ostloc, len(v), p64(plen)))