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NEWS
What's new in ZODB3 3.1.5?
Release date: 12-Feb-2004
There were no changes after the release candidate.
What's new in ZODB3 3.1.5 release candidate 1?
Release date: 20-Jan-2004
Fixed a serious bug in the new FileStorage pack implementation. If pack was called on the storage and passed a time earlier than a previous pack time, data could be lost. In other words, if there are any two pack calls, where the time argument passed to the second call was earlier than the first call, data loss could occur. The bug was fixed by causing the second call to raise a StorageError before performing any work.
Fixed a bug in BDBFullStorage that would cause tpc_abort() to fail if the aborted transaction had performed version operations or an undo that did not create new pickles.
What's new in ZODB3 3.1.4?
Release date: 11-Sep-2003
A new feature to allow removal of connection pools for versions was ported from Zope 2.6. This feature is needed by Zope to avoid denial of service attacks that allow a client to create an arbitrary number of version pools.
A pair of new scripts from Jim Fulton can be used to synthesize workloads and measure ZEO performance: see zodbload.py and zeoserverlog.py in the Tools directory. Note that these require Zope.
Tools/checkbtrees.py was strengthened in two ways:
- In addition to running the _check() method on each BTree B found, BTrees.check.check(B) is also run. The check() function was written after checkbtrees.py, and identifies kinds of damage B._check() cannot find.
- Cycles in the object graph no longer lead to unbounded output. Note that preventing this requires remembering the oid of each persistent object found, which increases the memory needed by the script.
What's new in ZODB3 3.1.3?
Release date: 18-Aug-2003
Fixed several critical ZEO bugs.
- If a storage server fails or times out between the vote and the finish, the ZEO cache could get populated with objects that didn't make it to the storage server.
- If a client loses its connection to the server near the end of a transaction, it is now guaranteed to get a ClientDisconnected error even if it reconnects before the transaction finishes. This is necessary because the server will always abort the transaction. In some cases, the client would never see an error for the aborted transaction.
- In tpc_finish(), reordered the calls so that the server's tpc_finish() is called (and must succeed) before we update the ZEO client cache.
- The storage name is now prepended to the sort key, to ensure a unique global sort order if storages are named uniquely. This can prevent deadlock in some unusual cases.
A variety of fixes and improvements to Berkeley storage (aka BDBStorage) were back-ported from ZODB 4. This release now contains the most current version of the Berkeley storage code. Many tests have been back-ported, but not all.
Modified the Windows tests to wait longer at the end of ZEO tests for the server to shut down. Before Python 2.3, there is no waitpid() on Windows, and, thus, no way to know if the server has shut down. The change makes the Windows ZEO tests much less likely to fail or hang, at the cost of increasing the time needed to run the tests.
Fixed a bug in ExtensionClass when comparing ExtensionClass instances. The code could raise RuntimeWarning under Python 2.3, and produce incorrect results on 64-bit platforms.
Fixed bugs in Tools/repozo.py, including a timing-dependent one that could cause the following invocation of repozo to do a full backup when an incremental backup would have sufficed.
Added Tools/README.txt that explains what each of the scripts in the Tools directory does.
There were many small changes and improvements to the test suite.
What's new in ZODB3 3.1.2 final?
Fixed bug in FileStorage pack that caused it to fail if it encountered an old undo record (status "u").
Fixed several bugs in FileStorage pack that could cause OverflowErrors for storages > 2 GB.
Fixed memory leak in TimeStamp.laterThan() that only occurred when it had to create a new TimeStamp.
Fixed two BTree bugs that were fixed on the head a while ago:
- bug in fsBTree that would cause byValue searches to end early. (fsBTrees are never used this way, but it was still a bug.)
- bug that lead to segfault if BTree was mutated via deletion while it was being iterated over.
What's new in ZODB3 3.1.2 beta 2?
Fixed critical race conditions in ZEO's cache consistency code that could cause invalidations to be lost or stale data to be written to the cache. These bugs can lead to data loss or data corruption. These bugs are relatively unlikely to be provoked in sites with few conflicts, but the possibility of failure existed any time an object was loaded and stored concurrently.
Fixed a bug in conflict resolution that failed to ghostify an object if it was involved in a conflict. (This code may be redundant, but it has been fixed regardless.)
The ZEO server was fixed so that it does not perform any I/O until all of a transactions' invalidations are queued. If it performs I/O in the middle of sending invalidations, it would be possible to overlap a load from a client with the invalidation being sent to it.
The ZEO cache now handles invalidations atomically. This is the same sort of bug that is described in the 3.1.2b1 section below, but it affects the ZEO cache.
Fixed several serious bugs in fsrecover that caused it to fail catastrophically in certain cases because it thought it had found a checkpoint (status "c") record when it was in the middle of the file.
What's new in ZODB3 3.1.2 beta 1?
ZODB
Invalidations are now processed atomically. Each transaction will see all the changes caused by an earlier transaction or none of them. Before this patch, it was possible for a transaction to see invalid data because it saw only a subset of the invalidations. This is the most likely cause of reported BTrees corruption, where keys were stored in the wrong bucket. When a BTree bucket splits, the bucket and the bucket's parent are both modified. If a transaction sees the invalidation for the bucket but not the parent, the BTree in memory will be internally inconsistent and keys can be put in the wrong bucket. The atomic invalidation fix prevents this problem.
A number of minor reference count fixes in the object cache were fixed. That's the cPickleCache.c file.
It was possible for a transaction that failed in tpc_finish() to lose the traceback that caused the failure. The transaction code was fixed to report the original error as well as any errors that occur while trying to recover from the original error.
ZEO
A ZEO client will not read from its cache during cache verification. This fix was necessary to prevent the client from reading inconsistent data.
The isReadOnly() method of a ZEO client was fixed to return the false when the client is connected to a read-only fallback server.
The sync() method of ClientStorage and the pending() method of a zrpc connection now do both input and output.
The short_repr() function used to generate log messages was fixed so that it does not blow up creating a repr of very long tuples.
Storages
FileStorage has a new pack() implementation that fixes several reported problems that could lead to data loss.
Two small bugs were fixed in DemoStorage. undoLog() did not handle its arguments correctly and pack() could accidentally delete objects created in versions.
Fixed trivial bug in fsrecover that prevented it from working at all.
FileStorage will use fsync() on Windows starting with Python 2.2.3.
FileStorage's commit version was fixed. It used to stop after the first object, leaving all the other objects in the version.
BTrees
Trying to store an object of a non-integer type into an IIBTree or OIBTree could leave the bucket in a variety of insane states. For example, trying
b[obj] = "I'm a string, not an integer"
where b is an OIBTree. This manifested as a refcount leak in the test suite, but could have been much worse (most likely in real life is that a seemingly arbitrary existing key would "go missing").
When deleting the first child of a BTree node with more than one child, a reference to the second child leaked. This could cause the entire bucket chain to leak (not be collected as garbage despite not being referenced anymore).
Other minor BTree leak scenarios were also fixed.
Other
Comparing a Missing.Value object to a C type that provide its own comparison operation could lead to a segfault when the Missing.Value was on the right-hand side of the comparison operator. The Missing class was fixed so that its coercion and comparison operations are safe.
Tools
Four tools are now installed by setup.py: fsdump.py, fstest.py, repozo.py, and zeopack.py.
What's new in ZODB3 3.1.1 beta 2?
Release date: 03-Feb-2003
The Transaction "hosed" feature is disabled in this release. If a transaction fails during the tpc_finish() it is not possible, in general, to know whether the storage is in a consistent state. For example, a ZEO server may commit the data and then fail before sending confirmation of the commit to the client. If multiple storages are involved in a transaction, the problem is exacerbated: One storage may commit the data while another fails to commit. In previous versions of ZODB, the database would set a global "hosed" flag that prevented any other transaction from committing until an administrator could check the status of the various failed storages and ensure that the database is in a consistent state. This approach favors data consistency over availability. The new approach is to log a panic but continue. In practice, availability seems to be more important than consistency. The failure mode is exceedingly rare in either case.
The BTrees-based fsIndex for FileStorage is enabled. This version of the index is faster to load and store via pickle and uses less memory to store keys. We had intended to enable this feature in an earlier release, but failed to actually do it; thus, it's getting enabled as a bug fix now.
Two rare bugs were fixed in BTrees conflict resolution. The most probable symptom of the bug would have been a segfault. The bugs were found via synthetic stress tests rather than bug reports.
A value-based consistency checker for BTrees was added. See the module BTrees.check for the checker and other utilities for working with BTrees.
A new script called repozo.py was added. This script, originally written by Anthony Baxter, provides an incremental backup scheme for FileStorage based storages.
zeopack.py has been fixed to use a read-only connection.
Various small autopack-related race conditions have been fixed in the Berkeley storage implementations. There have been some table changes to the Berkeley storages so any storage you created in 3.1.1b1 may not work. Part of these changes was to add a storage version number to the schema so these types of incompatible changes can be avoided in the future.
Removed the chance of bogus warnings in the FileStorage iterator.
ZEO
The ZEO version number was bumped to 2.0.2 on account of the following minor feature additions.
The performance of full cache verification has improved dramatically. XXX Get measurements from Jim -- somewhere in 2x-5x recall. The implementation was fixed to use the very-fast getSerial() method on the storage instead of the comparatively slow load().
The ZEO server has an optional timeout feature that will abort a connection that does not commit within a certain amount of time. The timeout works by closing the socket the client is using, causing both client and server to abort the transaction and continue. This is a drastic step, but can be useful to prevent a hung client or other bug from blocking a server indefinitely.
If a client was disconnected during a transaction, the tpc_abort() call did not properly reset the internal state about the transaction. The bug caused the next transaction to fail in its tpc_finish(). Also, any ClientDisconnected exceptions raised during tpc_abort() are ignored.
ZEO logging has been improved by adding more logging for important events, and changing the logging level for existing messages to a more appropriate level (usually lower).
What's new in ZODB3 3.1.1 beta 1?
Release date: 10-Dec-2002
It was possible for earlier versions of ZODB to deadlock when using multiple storages. If multiple transactions committed concurrently and both transactions involved two or more shared storages, deadlock was possible. This problem has been fixed by introducing a sortKey() method to the transaction and storage APIs that is used to define an ordering on transaction participants. This solution will prevent deadlocks provided that all transaction participants that use locks define a valid sortKey() method. A warning is raised if a participant does not define sortKey(). For backwards compatibility, BaseStorage provides a sortKey() that uses __name__.
Added code to ThreadedAsync/LoopCallback.py to work around a bug in asyncore.py: a handled signal can cause unwanted reads to happen.
A bug in FileStorage related to object uncreation was fixed. If an a transaction that created an object was undone, FileStorage could write a bogus data record header that could lead to strange errors if the object was loaded. An attempt to load an uncreated object now raises KeyError, as expected.
The restore() implementation in FileStorage wrote incorrect backpointers for a few corner cases involving versions and undo. It also failed if the backpointer pointed to a record that was before the pack time. These specific bugs have been fixed and new test cases were added to cover them.
A bug was fixed in conflict resolution that raised a NameError when a class involved in a conflict could not be loaded. The bug did not affect correctness, but prevent ZODB from caching the fact that the class was unloadable. A related bug prevented spurious AttributeErrors when a class could not be loaded. It was also fixed.
The script Tools/zeopack.py was fixed to work with ZEO 2. It was untested and had two silly bugs.
Some C extensions included standard header files before including Python.h, which is not allowed. They now include Python.h first, which eliminates compiler warnings in certain configurations.
The BerkeleyDB based storages have been merged from the trunk, providing a much more robust version of the storages. They are not backwards compatible with the old storages, but the decision was made to update them in this micro release because the old storages did not work for all practical purposes. For details, see Doc/BDBStorage.txt.
What's new in ZODB3 3.1 final?
Release date: 28-Oct-2002
If an error occurs during conflict resolution, the store will silently catch the error, log it, and continue as if the conflict was unresolvable. ZODB used to behave this way, and the change to catch only ConflictError was causing problems in deployed systems. There are a lot of legitimate errors that should be caught, but it's too close to the final release to make the substantial changes needed to correct this.
What's new in ZODB3 3.1 beta 3?
Release date: 21-Oct-2002
A small extension was made to the iterator protocol. The Record objects, which are returned by the per-transaction iterators, contain a new data_txn attribute. It is None, unless the data contained in the record is a logical copy of an earlier transaction's data. For example, when transactional undo modifies an object, it creates a logical copy of the earlier transaction's data. Note that this provide a stronger statement about consistency than whether the data in two records is the same; it's possible for two different updates to an object to coincidentally have the same data.
The restore() method was extended to take the data_txn attribute mentioned above as an argument. FileStorage uses the new argument to write a backpointer if possible.
A few bugs were fixed.
The setattr slot of the cPersistence C API was being initialized to NULL. The proper initialization was restored, preventing crashes in some applications with C extensions that used persistence.
The return value of TimeStamp's __cmp__ method was clipped to return only 1, 0, -1.
The restore() method was fixed to write a valid backpointer if the update being restored is in a version.
Several bugs and improvements were made to zdaemon, which can be used to run the ZEO server. The parent now forwards signals to the child as intended. Pidfile handling was improved and the trailing newline was omitted.
What's new in ZODB3 3.1 beta 2?
Release date: 4-Oct-2002
A few bugs have been fixed, some that were found with the help of Neal Norwitz's PyChecker.
The zeoup.py tool has been fixed to allow connecting to a read-only storage, when the --nowrite option is given.
Casey Duncan fixed a few bugs in the recent changes to undoLog().
The fstest.py script no longer checks that each object modified in a transaction has a serial number that matches the transaction id. This invariant is no longer maintained; several new features in the 3.1 release depend on it.
The ZopeUndo package was added. If ZODB3 is being used to run a ZEO server that will be used with Zope, it is usually best if the server and the Zope client don't share any software. The Zope undo framework, however, requires that a Prefix object be passed between client and server. To support this use, ZopeUndo was created to hold the Prefix object.
Many bugs were fixed in ZEO, and a couple of features added. See ZEO-NEWS.txt for details.
The ZODB guide included in the Doc directory has been updated. It is still incomplete, but most of the references to old ZODB packages have been removed. There is a new section that briefly explains how to use BTrees.
The zeoup.py tool connects using a read-only connection when --nowrite is specifified. This feature is useful for checking on read-only ZEO servers.
What's new in ZODB3 3.1 beta 1?
Release date: 12-Sep-2002
We've changed the name and version number of the project, but it's still the same old ZODB. There have been a lot of changes since the last release.
New ZODB cache
Toby Dickenson implemented a new Connection cache for ZODB. The cache is responsible for pointer swizzling (translating between oids and Python objects) and for keeping recently used objects in memory. The new cache is a big improvement over the old cache. It strictly honors its size limit, where size is specified in number of objects, and it evicts objects in least recently used (LRU) order.
Users should take care when setting the cache size, which has a default value of 400 objects. The old version of the cache often held many more objects than its specified size. An application may not perform as well with a small cache size, because the cache no longer exceeds the limit.
Storages
The index used by FileStorage was reimplemented using a custom BTrees object. The index maps oids to file offsets, and is kept in memory at all times. The new index uses about 1/4 the memory of the old, dictionary-based index. See the module ZODB.fsIndex for details.
A security flaw was corrected in transactionalUndo(). The transaction ids returned by undoLog() and used for transactionalUndo() contained a file offset. An attacker could construct a pickle with a bogus transaction record in its binary data, deduce the position of the pickle in the file from the undo log, then submit an undo with a bogus file position that caused the pickle to get written as a regular data record. The implementation was fixed so that file offsets are not included in the transaction ids.
Several storages now have an explicit read-only mode. For example, passing the keyword argument read_only=1 to FileStorage will make it read-only. If a write operation is performed on a read-only storage, a ReadOnlyError will be raised.
The storage API was extended with new methods that support the Zope Replication Service (ZRS), a proprietary Zope Corp product. We expect these methods to be generally useful. The methods are:
restore(oid, serialno, data, version, transaction)
Perform a store without doing consistency checks. A client can use this method to provide a new current revision of an object. The serialno argument is the new serialno to use for the object, not the serialno of the previous revision.
lastTransaction()
Returns the transaction id of the last committed transaction.
lastSerial(oid)
Return the current serialno for oid or None.
iterator(start=None, stop=None)
The iterator method isn't new, but the optional start and stop arguments are. These arguments can be used to specify the range of the iterator -- an inclusive range [start, stop].
FileStorage is now more cautious about creating a new file when it believes a file does not exist. This change is a workaround for bug in Python versions upto and including 2.1.3. If the interpreter was builtin without large file support but the platform had it, os.path.exists() would return false for large files. The fix is to try to open the file first, and decide whether to create a new file based on errno.
The undoLog() and undoInfo() methods of FileStorage can run concurrently with other methods. The internal storage lock is released periodically to give other threads a chance to run. This should increase responsiveness of ZEO clients when used with ZEO 2.
New serial numbers are assigned consistently for abortVersion() and commitVersion(). When a version is committed, the non-version data gets a new serial number. When a version is aborted, the serial number for non-version data does not change. This means that the abortVersion() transaction record has the unique property that its transaction id is not the serial number of the data records.
Berkeley Storages
Berkeley storage constructors now take an optional config argument, which is an instance whose attributes can be used to configure such BerkeleyDB policies as an automatic checkpointing interval, lock table sizing, and the log directory. See bsddb3Storage/BerkeleyBase.py for details.
A getSize() method has been added to all Berkeley storages.
Berkeley storages open their environments with the DB_THREAD flag.
Some performance optimizations have been implemented in Full storage, including the addition of a helper C extension when used with Python 2.2. More performance improvements will be added for the ZODB 3.1 final release.
A new experimental Autopack storage was added which keeps only a certain amount of old revision information. The concepts in this storage will be folded into Full and Autopack will likely go away in ZODB 3.1 final. ZODB 3.1 final will also have much improved Minimal and Full storages, which eliminate Berkeley lock exhaustion problems, reduce memory use, and improve performance.
It is recommended that you use BerkeleyDB 4.0.14 and PyBSDDB 3.4.0 with the Berkeley storages. See bsddb3Storage/README.txt for details.
BTrees
BTrees no longer ignore exceptions raised when two keys are compared.
Tim Peters fixed several endcase bugs in the BTrees code. Most importantly, after a mix of inserts and deletes in a BTree or TreeSet, it was possible (but unlikely) for the internal state of the object to become inconsistent. Symptoms then varied; most often this manifested as a mysterious failure to find a key that you knew was present, or that tree.keys() would yield an object that disgreed with the tree about how many keys there were.
If you suspect such a problem, BTrees and TreeSets now support a ._check() method, which does a thorough job of examining the internal tree pointers for consistency. It raises AssertionError if it finds any problems, else returns None. If ._check() raises an exception, the object is damaged, and rebuilding the object is the best solution. All known ways for a BTree or TreeSet object to become internally inconsistent have been repaired.
Other fixes include:
- Many fixes for range search endcases, including the "range search bug:" If the smallest key S in a bucket in a BTree was deleted, doing a range search on the BTree with S on the high end could claim that the range was empty even when it wasn't.
- Zope Collector #419: repaired off-by-1 errors and IndexErrors when slicing BTree-based data structures. For example, an_IIBTree.items()[0:0] had length 1 (should be empty) if the tree wasn't empty.
- The BTree module functions weightedIntersection() and weightedUnion() now treat negative weights as documented. It's hard to explain what their effects were before this fix, as the sign bits were getting confused with an internal distinction between whether the result should be a set or a mapping.
ZEO
For news about ZEO2, see the file ZEO-NEWS.txt.
This version of ZODB ships with two different versions of ZEO. It includes ZEO 2.0 beta 1, the recommended new version. (ZEO 2 will reach final release before ZODB3.) The ZEO 2.0 protocol is not compatible with ZEO 1.0, so we have also included ZEO 1.0 to support people already using ZEO 1.0.
Other features
When a ConflictError is raised, the exception object now has a sensible structure, thanks to a patch from Greg Ward. The exception now uses the following standard attributes: oid, class_name, message, serials. See the ZODB.POSException.ConflictError doc string for details.
It is now easier to customize the registration of persistent objects with a transaction. The low-level persistence mechanism in cPersistence.c registers with the object's jar instead of with the current transaction. The jar (Connection) then registers with the transaction. This redirection would allow specialized Connections to change the default policy on how the transaction manager is selected without hacking the Transaction module.
Empty transactions can be committed without interacting with the storage. It is possible for registration to occur unintentionally and for a persistent object to compensate by making itself as unchanged. When this happens, it's possible to commit a transaction with no modified objects. The change allows such transactions to finish even on a read-only storage.
Two new tools were added to the Tools directory. The analyze.py script, based on a tool by Matt Kromer, prints a summary of space usage in a FileStorage Data.fs. The checkbtrees.py script scans a FileStorage Data.fs. When it finds a BTrees object, it loads the object and calls the _check method. It prints warning messages for any corrupt BTrees objects found.
Documentation
The user's guide included with this release is still woefully out of date.
Other bugs fixed
If an exception occurs inside an _p_deactivate() method, a traceback is printed on stderr. Previous versions of ZODB silently cleared the exception.
ExtensionClass and ZODB now work correctly with a Python debug build.
All C code has been fixed to use a consistent set of functions from the Python memory API. This allows ZODB to be used in conjunction with pymalloc, the default allocator in Python 2.3.
zdaemon, which can be used to run a ZEO server, more clearly reports the exit status of its child processes.
The ZEO server will reinitialize zLOG when it receives a SIGHUP. This allows log file rotation without restarting the server.
What's new in StandaloneZODB 1.0 final?
Release date: 08-Feb-2002
All copyright notices have been updated to reflect the fact that the ZPL 2.0 covers this release.
Added a cleanroom PersistentList.py implementation, which multiply inherits from UserDict and Persistent.
Some improvements in setup.py and test.py for sites that don't have the Berkeley libraries installed.
A new program, zeoup.py was added which simply verifies that a ZEO server is reachable. Also, a new program zeopack.py was added which connects to a ZEO server and packs it.
What's new in StandaloneZODB 1.0 c1?
Release Date: 25-Jan-2002
This was the first public release of the StandaloneZODB from Zope Corporation. Everything's new! :)