https://bugzilla.wikimedia.org/show_bug.cgi?id=27320
Summary: MessageBlobStore::clear() causes scaling problems on
multi-server setups with CDB l10ncache
Product: MediaWiki
Version: 1.18-svn
Platform: All
OS/Version: All
Status: NEW
Severity: enhancement
Priority: Normal
Component: Resource Loader
AssignedTo: roan.katt...@gmail.com
ReportedBy: roan.katt...@gmail.com
CC: tstarl...@wikimedia.org, roan.katt...@gmail.com,
tpars...@wikimedia.org
We had to disable MessageBlobStore::clear() on WMF and replace it with a
maintenance script to run upon sync, because on multi-server setups where
l10ncache is in CDB, LocalisationCache::recache() is run once per server per
language, causing the MBS to be cleared lots of times. This led to DB deadlocks
and possibly to other performance issues.
I guess the least we can do is offer a $wg variable to disable clear(). A
better solution, suggested by Tim, would be to add
CacheDependency::getModifiedTime(), add a way to retrieve the maximum mtime
from LocalisationCache, and use that in the startup module to conditionally
call MessageBlobStore::clear() before retrieving any module timestamps. This
would scale because the startup module is cached for 5 minutes.
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