We've twice tried to upgrade our MediaWiki site (
www.uesp.net) running
MediaWiki 1.14 to 1.19 but had the same problem each time. The basic
upgrade process and resulting issue goes like:
- Set wiki to read only mode.
- Backup database and copy into a new database.
- Upgrade the new database to 1.19 (no issues though it takes an hour).
- Test 1.19 wiki (no issues seen including aggressive load testing with ab).
- Switch 1.19 to "live" site.
- Right away the database server begins to be overloaded with hundreds
of "DELETE
FROM l10n_cache WHERE lc_lang=en;" queries. Some page views get through but
eventually the Apache servers fill up with connections waiting for the database
server which also fills up with connections that never terminate.
- Switch back the live site to 1.14. The database server has to be forced
closed and restarted to restore service (the delete queries never finish).
A few possible causes:
- One of our extensions or custom code changes is causing an issue.
Unfortunately,
some of the more complex/custom extensions cannot be disabled without
breaking the site.
- Increased database load: Our db servers are very underused and a
conservative estimate is they would work fine with a 20x load increase. A
small load increase from the apparent changes between 1.14 and 1.19
shouldn't cause this level of database issue.
- Our database was originally created with a very old MediaWiki (1.3 I
think). While the upgrade from 1.14 to 1.19 works perhaps there are
lingering issues that need the wiki database to be recreated from scratch
somehow.
- An issue with the MediaWiki localization db cache when used with a high
traffic site.
My next guess on what to try is to set "$wgCacheDirectory" to a local
directory which should completely avoid using the database for any
localization messages if I understand things correctly. Unfortunately, I
have no way of testing if this works without running through another
complete upgrade attempt.
Any suggestions or ideas on what to try would be appreciated....
------------------------
Dave Humphrey - dave(a)uesp.net
Server Admin - the Unofficial Elder Scrolls Pages -
www.uesp.net