ZODB 5.2.0

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.


.. contents::

====
ZODB
====

Introduction
============

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.

Compatibility
=============

ZODB 5 requires Python 2.7 (>= 2.7.9) or Python >= 3.3.

Documentation
=============

See http://zodb-docs.readthedocs.io/en/latest/

For developers of ZODB
======================

Building
---------

Bootstrap buildout, if necessary using ``bootstrap.py``::

python bootstrap.py

Run the buildout::

bin/buildout

Testing
-------

The ZODB checkouts are `buildouts <http://www.python.org/pypi/zc.buildout>`_.
When working from a ZODB checkout, first run the bootstrap.py script
to initialize the buildout:

% python bootstrap.py

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

OK

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

OK

Generating docs
---------------

cd to the doc directory and::

make html

Contributing
------------

Almost any code change should include tests.

Any change that changes features should include documentation updates.

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.

License
=======

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
================

See http://zodb.org/


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================
Change History
================

5.2.0 (2017-02-09)
==================

- Call new afterCompletion API on storages to allow them to free
resources after transaction complete. See:
https://github.com/zodb/relstorage/issues/147

- Take advantage of the new transaction-manager explicit mode to avoid
starting transactions unnecessarily when transactions end.

- ``Connection.new_oid`` delegates to its storage, not the DB. This is
helpful for improving concurrency in MVCC storages like RelStorage.
See `issue 139 <https://github.com/zopefoundation/ZODB/issues/139`_.

- ``persistent`` is no longer required at setup time.
See `issue 119 <https://github.com/zopefoundation/ZODB/issues/119>`_.

- ``Connection.close`` and ``Connection.open`` no longer race on
``self.transaction_manager``, which could lead to
``AttributeError``. This was a bug introduced in 5.0.1. See `issue
142 <https://github.com/zopefoundation/ZODB/pull/143>`_.


5.1.1 (2016-11-18)
==================

- Fixed: ``ZODB.Connection.TransactionMetaData`` didn't support custom data
storage that some storages rely on.

5.1.0 (2016-11-17)
==================

- ZODB now translates transaction meta data, ``user`` and
``description`` from text to bytes before passing them to storages,
and converts them back to text when retrieving them from storages in
the ``history``, ``undoLog`` and ``undoInfo`` methods.

The ``IDatabase`` interface was updated to reflect that ``history``,
``undoLog`` and ``undoInfo`` are available on database objects.
(They were always available, but not documented in the interface.)

5.0.1 (2016-11-17)
==================

- Fix an AttributeError that DemoStorage could raise if it was asked
to store a blob into a temporary changes before reading a blob. See
`issue 103 <https://github.com/zopefoundation/ZODB/issues/103>`_.

- Call _p_resolveConflict() even if a conflicting change doesn't change the
state. This reverts to the behaviour of 3.10.3 and older.

- Closing a Connection now reverts its ``transaction_manager`` to
None. This helps prevent errors and release resources when the
``transaction_manager`` was the (default) thread-local manager. See
`issue 114 <https://github.com/zopefoundation/ZODB/issues/114>`_.

- Many docstrings have been improved.

5.0.0 (2016-09-06)
==================

Major internal improvements and cleanups plus:

- 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.

- 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.

- 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.

5.0.0b1 (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.

5.0.0a4 (2016-07-05)
====================

See 4.4.2.

5.0.0a3 (2016-07-01)
====================

See 4.4.1.

5.0.0a2 (2016-07-01)
====================

See 4.4.0.

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 <http://www.neoppod.org/>`_,
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
https://github.com/zopefoundation/ZODB/pull/42.

- Add support for Python 3.5.

- Avoid failure during cleanup of nested databases that provide MVCC
on storage level (Relstorage).
https://github.com/zopefoundation/ZODB/issues/45

- Remove useless dependency to `zdaemon` in setup.py. 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.
https://github.com/zopefoundation/ZODB/pull/52

- DemoStorage: add support for conflict resolution and fix history()
https://github.com/zopefoundation/ZODB/pull/58

- Fixed a test that depended on implementation-specific behavior in tpc_finish

4.2.0 (2015-06-02)
==================

- Declare conditional dependencies using PEP-426 environment markers
(fixing interation between pip 7's wheel cache and tox). See
https://github.com/zopefoundation/ZODB/issues/36.

4.2.0b1 (2015-05-22)
====================

- Log failed conflict resolution attempts at ``DEBUG`` level. See:
https://github.com/zopefoundation/ZODB/pull/29.

- 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 https://github.com/zopefoundation/ZODB/pull/21.

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
https://github.com/zopefoundation/ZODB/issues/16

- 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 ``setup.py 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.

.. note::

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 setup.py 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.

https://bugs.launchpad.net/zodb/+bug/993350

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


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