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ZODB 5.0.0b1

Zope Object Database: object database and persistence

The Zope Object Database provides an object-oriented database for Python that provides a high-degree of transparency. Applications can take advantage of object database features with few, if any, changes to application logic. ZODB includes features such as a plugable storage interface, rich transaction support, and undo.



The ZODB package provides a set of tools for using the Zope Object Database (ZODB).

Our primary development platforms are Linux and Mac OS X. The test suite should pass without error on these platforms and, hopefully, Windows, although it can take a long time on Windows – longer if you use ZoneAlarm.


ZODB 4.3 requires Python 2.7 or Python >= 3.3.

Travis: winbot:


You must have Python installed. If you’re using a system Python install, make sure development support is installed too.

You also need the transaction, BTrees, persistent, six, zc.lockfile, ZConfig, zodbpickle, zope.interface packages, and optionally manuel and zope.testing. If you don’t have them and you can connect to the Python Package Index, then these will be installed for you if you don’t have them.


ZODB is released as a distutils package. The easiest ways to build and install it are to use easy_install, or zc.buildout.

To install by hand, first install the dependencies listed in Prerequisites. These can be found in the Python Package Index.

To run the tests, use the test setup command:

python test

It will download dependencies if needed. If this happens, ou may get an import error when the test command gets to looking for tests. Try running the test command a second time and you should see the tests run.

python test

To install, use the install command:

python install

Testing for Developers

The ZODB checkouts are buildouts. When working from a ZODB checkout, first run the script to initialize the buildout:

% python

and then use the buildout script to build ZODB and gather the dependencies:

% bin/buildout

This creates a test script:

% bin/test -v

This command will run all the tests, printing a single dot for each test. When it finishes, it will print a test summary. The exact number of tests can vary depending on platform and available third-party libraries.:

Ran 1182 tests in 241.269s


The test script has many more options. Use the -h or --help options to see a file list of options. The default test suite omits several tests that depend on third-party software or that take a long time to run. To run all the available tests use the --all option. Running all the tests takes much longer.:

Ran 1561 tests in 1461.557s


Maintenance scripts

Several scripts are provided with the ZODB and can help for analyzing, debugging, checking for consistency, summarizing content, reporting space used by objects, doing backups, artificial load testing, etc. Look at the ZODB/script directory for more informations.


ZODB is distributed under the Zope Public License, an OSI-approved open source license. Please see the LICENSE.txt file for terms and conditions.

More information


There is a Mailman mailing list in place to discuss all issues related to ZODB. You can send questions to

or subscribe at

and view its archives at

Note that Zope Corp mailing lists have a subscriber-only posting policy.

Bugs and Patches

Bug reports and patches should be added to the Launchpad:

Change History

5.0.0b1 (2016-08-04)

  • fstail: print the txn offset and header size, instead of only the data offset. fstail can now be used to truncate a DB at the right offset.

Numerous internal cleanups, including:

  • Changed the way the root object was created. Now the root object is created using a database connection, rather than by making low-level storage calls.
  • Drop support for the old commit protocol.
  • Internal FileStorage-undo fixes that should allow undo in some cases where it didn’t work before.
  • Drop the version argument to some methods where it was the last argument and optional.

5.0.0a6 (2016-07-21)

  • Added a connection prefetch method that can be used to request that a storage prefect data an application will need:

    conn.prefetch(obj, ...)

    Where arguments can be objects, object ids, or iterables of objects or object ids.

    Added optional prefetch methods to the storage APIs. If a storage doesn’t support prefetch, then the connection prefetch method is a noop.

5.0.0a5 (2016-07-06)

Drop support for old commit protocol. All of the build-in storages implement the new protocol. This new protocol allows storages to provide better write performance by allowing multiple commits to execute in parallel.

5.0.0a1 (2016-06-20)

Major internal implementation changes to the Multi Version Concurrency Control (MVCC) implementation:

  • For storages that implement IMVCCStorage (RelStorage), no longer implement MVCC in ZODB.

  • For other storages, MVCC is implemented using an additional storage layer. This underlying layer works by calling loadBefore. The low-level storage load method isn’t used any more.

    This change allows server-nased storages like ZEO and NEO to be implemented more simply and cleanly.

4.4.3 (2016-08-04)

  • Internal FileStorage-undo fixes that should allow undo in some cases where it didn’t work before.
  • fstail: print the txn offset and header size, instead of only the data offset. fstail can now be used to truncate a DB at the right offset.

4.4.2 (2016-07-08)

Better support of the new commit protocol. This fixes issues with blobs and undo. See pull requests #77, #80, #83

4.4.1 (2016-07-01)

Added IMultiCommitStorage to directly represent the changes in the 4.4.0 release and to make complient storages introspectable.

4.4.0 (2016-06-30)

This release begins evolution to a more effcient commit protocol that allows storage implementations, like NEO, to support multiple transactions committing at the same time, for greater write parallelism.

This release updates IStorage:

  • The committed transaction’s ID is returned by tpc_finish, rather than being returned in response store and tpc_vote results.
  • tpc_vote is now expected to return None or a list of object ids for objects for which conflicts were resolved.

This release works with storages that implemented the older version of the storage interface, but also supports storages that implement the updated interface.

4.3.1 (2016-06-06)

  • Fixed: FileStorage loadBefore didn’t handle deleted/undone data correctly.

4.3.0 (2016-05-31)

  • Drop support for Python 2.6 and 3.2.
  • Make the zodbpickle dependency required and not conditional. This fixes various packaging issues involving pip and its wheel cache. zodbpickle was only optional under Python 2.6 so this change only impacts users of that version. See
  • Add support for Python 3.5.
  • Avoid failure during cleanup of nested databases that provide MVCC on storage level (Relstorage).
  • Remove useless dependency to zdaemon in Remove ZEO documentation. Both were leftovers from the time where ZEO was part of this repository.
  • Fix possible data corruption after FileStorage is truncated to roll back a transaction.
  • DemoStorage: add support for conflict resolution and fix history()
  • Fixed a test that depended on implementation-specific behavior in tpc_finish

4.2.0 (2015-06-02)

4.2.0b1 (2015-05-22)

  • Log failed conflict resolution attempts at DEBUG level. See:
  • Fix command-line parsing of --verbose and --verify arguments. (The short versions, -v and -V, were parsed correctly.)
  • Add support for PyPy.
  • Fix the methods in ZODB.serialize that find object references under Python 2.7 (used in scripts like referrers, netspace, and fsrecover among others). This requires the addition of the zodbpickle dependency.
  • FileStorage: fix an edge case when disk space runs out while packing, do not leave the .pack file around. That would block any write to the to-be-packed Data.fs, because the disk would stay at 0 bytes free. See

4.1.0 (2015-01-11)

  • Fix registration of custom logging level names (“BLATHER”, “TRACE”).

    We have been registering them in the wrong order since 2004. Before Python 3.4, the stdlib logging module masked the error by registering them in both directions.

  • Add support for Python 3.4.

4.0.1 (2014-07-13)

  • Fix POSKeyError during transaction.commit when after savepoint.rollback. See
  • Ensure that the pickler used in PyPy always has a persistent_id attribute (inst_persistent_id is not present on the pure-Python pickler). (PR #17)
  • Provide better error reporting when trying to load an object on a closed connection.

4.0.0 (2013-08-18)

Finally released.

4.0.0b3 (2013-06-11)

  • Switch to using non-backward-compatible pickles (protocol 3, without storing bytes as strings) under Python 3. Updated the magic number for file-storage files under Python3 to indicate the incompatibility.
  • Fixed: A UnicodeDecodeError could happen for non-ASCII OIDs when using bushy blob layout.

4.0.0b2 (2013-05-14)

  • Extended the filename renormalizer used for blob doctests to support the filenames used by ZEO in non-shared mode.
  • Added url parameter to setup() (PyPI says it is required).

4.0.0b1 (2013-05-10)

  • Skipped non-unit tests in test. Use the buildout to run tests requiring “layer” support.
  • Included the filename in the exception message to support debugging in case loadBlob does not find the file.
  • Added support for Python 3.2 / 3.3.


ZODB 4.0.x is supported on Python 3.x for new applications only. Due to changes in the standard library’s pickle support, the Python3 support does not provide forward- or backward-compatibility at the data level with Python2. A future version of ZODB may add such support.

Applications which need migrate data from Python2 to Python3 should plan to script this migration using separte databases, e.g. via a “dump-and-reload” approach, or by providing explicit fix-ups of the pickled values as transactions are copied between storages.

4.0.0a4 (2012-12-17)

  • Enforced usage of bytes for _p_serial of persistent objects (fixes compatibility with recent persistent releases).

4.0.0a3 (2012-12-01)

  • Fixed: An elaborate test for trvial logic corrupted module state in a

    way that made other tests fail spuriously.

4.0.0a2 (2012-11-13)

Bugs Fixed

  • An unneeded left-over setting in caused installation with pip to fail.

4.0.0a1 (2012-11-07)

New Features

  • The persistent and BTrees packages are now released as separate distributions, on which ZODB now depends.
  • ZODB no longer depends on zope.event. It now uses ZODB.event, which uses zope.event if it is installed. You can override ZODB.event.notify to provide your own event handling, although zope.event is recommended.
  • BTrees allowed object keys with insane comparison. (Comparison inherited from object, which compares based on in-process address.) Now BTrees raise TypeError if an attempt is made to save a key with comparison inherited from object. (This doesn’t apply to old-style class instances.)

Bugs Fixed

  • Ensured that the export file and index file created by repozo share the same timestamp.

  • Pinned the transaction and manuel dependencies to Python 2.5- compatible versions when installing under Python 2.5.


Please see doc/HISTORY.txt for changelog entries for older versions of ZODB.

File Type Py Version Uploaded on Size
ZODB-5.0.0b1.tar.gz (md5) Source 2016-08-04 495KB