[ZODB-Dev] DirectoryStorage 1.1.2

[Toby Dickenson]

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Announcing the release of DirectoryStorage 1.1.2

A serious bug has been discovered in all previous versions. Version 1.1.2 
contains a fix, and no other changes. All users are encouraged to upgrade at 
their convenience.

Problem Details:
Under high write pressure it was possible for DirectoryStorage to neglect to 
flush all necessary files into the main storage directory when entering 
snapshot mode. This could happen if a transaction is committed concurrently 
with entry to snapshot mode. The effects of this bug include incomplete 
backups, incomplete replicas, and spurious errors when packing.

Mitigating factors:
1. This does not corrupt the main storage, although it can
   lead to corrupt backups or replicas.
2. The corruption will certainly be detected by checkds. You
   do run checkds on a snapshot before taking a backup, dont
   you?
3. A backup/replica may be corrupt due to a missing file.
   Any missing file will certainly be included the next
   backup/replica.
4. I believe that the problems with backup and replication
   cant happen when the storage is inside a ZEO server,
   thanks to ZEO's threading architecture. DirectoryStorage
   inside ZEO is still vulnerable to spurious errors when
   packing.

Download: 
http://sourceforge.net/project/showfiles.php?group_id=53818&release_id=160099

This bug was detected using a recent unit test added to ZODB by Jeremy to test 
a FileStorage corner case. Anyone wanting to repeat these unit tests will 
need the CVS trunks of both projects.

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