Supporting the UW Web

I edited the MediaWiki instructions today to include a note that users should disable InnoDB before installing MediaWiki. If people do this, then their wikis will work after MySQL has been automatically restarted by cron after a system restart. If people don’t do this, then I have to fix their databases after a system restart due to stale NFS locks.
I wrote about this topic last Monday.  Since then I read about MediaWiki and MySQL storage engines, and tried an experiment where I converted the InnoDB tables my MediaWiki installation was using to MyISAM tables.  As far as I can tell, MediaWiki works fine using MyISAM.

Here’s a brief mention on the MySQL Reference Manual of problems that InnoDB has when its data or log files are stored on NFS volumes: Restrictions on InnoDB Tables

Warning

It is not a good idea to configure to use datafiles or logfiles on NFS volumes. Otherwise, the files might be locked by other processes and become unavailable for use by MySQL.

The issue in the cases I see commonly seems to be that when the NFS client system is rebooted, the NFS server does not get any notice that locks should be released on the files.  When the NFS client comes back up from the reboot and reconnects to the server, those files are still locked, and the client cannot get a new lock on them.  This causes MySQL to issue errors like the following:

InnoDB: Unable to lock ./ibdata1, error: 11
InnoDB: Check that you do not already have another mysqld process
InnoDB: using the same InnoDB data or log files.

and this:

InnoDB: Operating system error number 11 in a file operation.
InnoDB: Error number 11 means ‘Resource temporarily unavailable’.
InnoDB: Some operating system error numbers are described at
InnoDB: http://dev.mysql.com/doc/refman/5.0/en/operating-system-error-codes.html
InnoDB: Could not open or create data files.
InnoDB: If you tried to add new data files, and it failed here,
InnoDB: you should now edit innodb_data_file_path in my.cnf back
InnoDB: to what it was, and remove the new ibdata files InnoDB created
InnoDB: in this failed attempt. InnoDB only wrote those files full of
InnoDB: zeros, but did not yet use them in any way. But be careful: do not
InnoDB: remove old data files which contain your precious data!