A number of things try to write to the database when read-only mode is on. This can produce
annoying error messages when attached to a really read-only database that's locked, or can cause
data corruption if you're simply implicitly assuming the wiki will not write.

The user_newtalk expiration check on login is one example. Other expirations (objectcache,
ipblocks) should be checked also, and there may be others.

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Severity: normal