Akonadiserver: rework handling of database deadlocks.

Authored by dfaure on Apr 6 2019, 9:47 PM.



We can't just replay the SQL commands, that's too low-level: if we do
INSERT, then use the resulting ID into e.g. another INSERT command, at replay
time we might get a different ID from the first command, and then insert
the wrong ID in the second one...

So instead we want to re-run the entire handler's parseStream(), which we
do by throwing a DbDeadlockException (from QueryBuilder), and catching that
in the caller (Connection) using a helper class (DbDeadlockCatcher, unittested)
which retries up to 5 times.

For this to work, it means:

  • we must also rollback any chances made to in-memory caches (done by

clearing those caches, good enough since DB deadlocks are rare)

  • ItemModifyJob which sends parts on demand, shouldn't delete after

sending (it might be asked again) -- this was hit by GidTest (fetchAndSetGid).

Still TODO:

  • delaying the updating of intervalChecker and cacheCleaner by NotificationCollector until commit time;
  • checking other users of QueryBuilder (who now can get a DbDeadlockException...)
Test Plan

all this was triggered by a unittest that creates 10 sessions
and adds 10 different attributes to the same time, one in each session. This very
often hits the DB deadlock scenario.

Diff Detail

R165 Akonadi
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dfaure created this revision.Apr 6 2019, 9:47 PM
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dfaure requested review of this revision.Apr 6 2019, 9:47 PM
dvratil requested changes to this revision.Apr 6 2019, 10:56 PM
dvratil added inline comments.

Use "" instead of <>, it is a local include (while private is another library)




Not related, keep it in DataStore, please.


Use a named constant instead of a magic number.

20 ↗(On Diff #55606)

Not needed.

This revision now requires changes to proceed.Apr 6 2019, 10:56 PM
dfaure updated this revision to Diff 55629.Apr 7 2019, 7:50 AM

Make requested changes

dvratil accepted this revision.Apr 7 2019, 9:25 AM
This revision is now accepted and ready to land.Apr 7 2019, 9:25 AM
This revision was automatically updated to reflect the committed changes.