[ZODB-Dev] RelStorage MySQL - StorageError: Unable to acquire commit lock

[Jürgen Herrmann]

On Wed, August 12, 2009 22:23, Rudá Porto Filgueiras wrote:
> I begin to use RelStorage in a production site with Plone 2.5.
> Everything was running without failures since 01 august 2009.
> But today after a failure in tpc_abort, all instances conneceted to
> MySQL can't acquire commit lock.
>
> Follow tpc_abort traceback:
>
> 2009-08-12T14:12:08 ERROR txn.1115806016 Error in tpc_abort() on
> manager <MultiObjectResourceAdapter for <ZODB.DB.TransactionalUndo
> object at 0x210f6790> at 654293328>
> Traceback (most recent call last):
>   File
> "/usr/local/zope/agecom-virtual/eggs/ZODB3-3.7.3_polling-py2.4-linux-x86_64.egg/transaction/_transaction.py",
> line 533, in _cleanup
>     rm.tpc_abort(self)
>   File
> "/usr/local/zope/agecom-virtual/eggs/ZODB3-3.7.3_polling-py2.4-linux-x86_64.egg/transaction/_transaction.py",
> line 628, in tpc_abort
>     self.manager.tpc_abort(txn)
>   File
> "/usr/local/zope/agecom-virtual/eggs/ZODB3-3.7.3_polling-py2.4-linux-x86_64.egg/ZODB/BaseStorage.py",
> line 194, in tpc_abort
>     self._abort()
>   File
> "/usr/local/zope/agecom-virtual/eggs/RelStorage-1.2.0b2-py2.4.egg/relstorage/relstorage.py",
> line 710, in _abort
>     self._rollback_load_connection()
>   File
> "/usr/local/zope/agecom-virtual/eggs/RelStorage-1.2.0b2-py2.4.egg/relstorage/relstorage.py",
> line 166, in _rollback_load_connection
>     self._load_conn.rollback()
> OperationalError: (2006, 'MySQL server has gone away')
>
> And after, all instances report this exeption:
>
> 2009-08-12T14:21:53 ERROR Zope.SiteErrorLog
> http://adm.agecom.ba.gov.br/login_form
> Traceback (innermost last):
>   Module ZPublisher.Publish, line 121, in publish
>   Module Zope2.App.startup, line 240, in commit
>   Module transaction._manager, line 96, in commit
>   Module transaction._transaction, line 395, in commit
>   Module transaction._transaction, line 498, in _commitResources
>   Module ZODB.Connection, line 730, in tpc_vote
>   Module relstorage.relstorage, line 675, in tpc_vote
>   Module relstorage.relstorage, line 659, in _vote
>   Module relstorage.relstorage, line 566, in _prepare_tid
>   Module relstorage.adapters.mysql, line 506, in start_commit
>   Module relstorage.adapters.mysql, line 672, in _hold_commit_lock
> StorageError: Unable to acquire commit lock
>
> I solve the problem restarting all instances, and the site became
> operational again, but I have some questions:
>
> This can be a bug or there is any problem in my enviroment/application?
> There is another solution to release commit lock without restart all instances?
>
> Cheers,
>
> --
> Rudá Porto Filgueiras
> http://python-blog.blogspot.com
> _______________________________________________
> For more information about ZODB, see the ZODB Wiki:
> http://www.zope.org/Wikis/ZODB/
>
> ZODB-Dev mailing list  -  ZODB-Dev at zope.org
> http://mail.zope.org/mailman/listinfo/zodb-dev
>

i just came back from reading relstorage code (research work for
radosstorage) and the lock is actually held on the mysql server.
my guess is that the connection drop you experience earlier left
the lock in place on the mysql-server. obviously the mysql-server
did not notice you connection dying, otherwise it would have
released the lock,see
http://dev.mysql.com/doc/refman/5.0/en/miscellaneous-functions.html#function_get-lock
probably restarting mysql would have solved your issue?!

regards, jürgen
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