What's new on ZODB 3.8.0
========================

General
-------

- The ZODB Storage APIs have been documented and cleaned up.

- ZODB versions are now officially deprecated and support for them
  will be removed in ZODB 3.9.  (They have been widely recognized as
  deprecated for quite a while.)

- Changed the automatic garbage collection when opening a connection to only
  apply the garbage collections on those connections in the pool that are
  closed. (This fixed issue 113932.)

- (3.8.0b3) Document conflict resolution (see ZODB/ConflictResolution.txt).

- (3.8.0b3) Bugfix the situation in which comparing persistent objects (for
  instance, as members in BTree set or keys of BTree) might cause data
  inconsistency during conflict resolution.

- (3.8.0b3) Support multidatabase references in conflict resolution.

- (3.8.0b3) Make it possible to examine oid and (in some situations) database
  name of persistent object references during conflict resolution.

- (3.8.0b3) Added missing data attribute for conflict errors.

- (3.8.0b5) Fixed bug 153316: persistent and BTrees gave errors on x86_64
  Intel XEON platforms.

ZEO
---

- (3.8.0b6) Bug #98275: Made ZEO cache more tolerant when invalidating current
  versions of objects.

- (3.8.0b4, 3.8.0b5) Fixed a serious bug that could cause client I/O to stop
  (hang). This was accomonied by a critical log message along the
  lines of: "RuntimeError: dictionary changed size during iteration".
  (In b4, the bug was only partially fixed.)

- (3.8a1) ZEO's strategoes for avoiding client cache verification were
  improved in the case that servers are restarted.  Before, if
  transactions were committed after the restart, clients that were up
  to date or nearly up to date at the time of the restart and then
  connected had to verify their caches.  Now, it is far more likely
  that a client that reconnects soon after a server restart won't have
  to verify its cache.

- (3.8a1) Fixed a serious bug that could cause clients that disconnect from and
  reconnect to a server to get bad invalidation data if the server
  serves multiple storages with active writes.

- (3.8a1) It is now theoretically possible to use a ClientStorage in a storage
  server.  This might make it possible to offload read load from a
  storage server at the cost of increasing write latency.  This should
  increase write throughput by offloading reads from the final storage
  server.  This feature is somewhat experimental.  It has tests, but
  hasn't been used in production.

Transactions
------------

- (3.8a1) Add a doom() and isDoomed() interface to the transaction module.

  First step towards the resolution of
  http://www.zope.org/Collectors/Zope3-dev/655

  A doomed transaction behaves exactly the same way as an active transaction
  but raises an error on any attempt to commit it, thus forcing an abort.

  Doom is useful in places where abort is unsafe and an exception cannot be
  raised.  This occurs when the programmer wants the code following the doom to
  run but not commit. It is unsafe to abort in these circumstances as a
  following get() may implicitly open a new transaction.

  Any attempt to commit a doomed transaction will raise a DoomedTransaction
  exception.

- (3.8a1) Clean up the ZODB imports in transaction.

  Clean up weird import dance with ZODB. This is unnecessary since the
  transaction module stopped being imported in ZODB/__init__.py in rev 39622.

- (3.8a1) Support for subtransactions has been removed in favor of
  save points.

Blobs
-----

- (3.8b5) Fixed bug #130459: Packing was broken by uncommitted blob data.

- (3.8b4) Fixed bug #127182: Blobs were subclassable which was not desired.

- (3.8b3) Fixed bug #126007: tpc_abort had untested code path that was
  broken.

- (3.8b3) Fixed bug #129921: getSize() function in BlobStorage could not
  deal with garbage files

- (3.8b1) Updated the Blob implementation in a number of ways.  Some
  of these are backward incompatible with 3.8a1:

  o The Blob class now lives in ZODB.blob

  o The blob openDetached method has been replaced by the committed method.

- (3.8a1) Added new blob feature. See the ZODB/Blobs directory for
  documentation.

  ZODB now handles (reasonably) large binary objects efficiently. Useful to
  use from a few kilobytes to at least multiple hundred megabytes.

BTrees
------

- (3.8a1) Added support for 64-bit integer BTrees as separate types.  

  (For now, we're retaining compile-time support for making the regular
  integer BTrees 64-bit.)

- (3.8a1) Normalize names in modules so that BTrees, Buckets, Sets, and
  TreeSets can all be accessed with those names in the modules (e.g.,
  BTrees.IOBTree.BTree).  This is in addition to the older names (e.g.,
  BTrees.IOBTree.IOBTree).  This allows easier drop-in replacement, which
  can especially be simplify code for packages that want to support both
  32-bit and 64-bit BTrees.

- (3.8a1) Describe the interfaces for each module and actually declare
  the interfaces for each.

- (3.8a1) Fix module references so klass.__module__ points to the Python
  wrapper module, not the C extension.

- (3.8a1) introduce module families, to group all 32-bit and all 64-bit
  modules.
