On 2013-11-21 16:25:02 +0200, Heikki Linnakangas wrote: > Hmm. All callers of RecoveryInProgress() must be prepared to handle the case > that RecoveryInProgress() returns true, but the system is no longer in > recovery. No matter what locking we do in RecoveryInProgress(), the startup > process might finish recovery just after RecoveryInProgress() has returned.
True. > What about the attached? It reads the shared variable without a lock or > barrier. If it returns 'true', but the system in fact just exited recovery, > that's OK. As explained above, all the callers must tolerate that anyway. > But if it returns 'false', then it performs a full memory barrier, which > should ensure that it sees any other shared variables as it is after the > startup process cleared SharedRecoveryInProgress (notably, > XLogCtl->ThisTimeLineID). I'd argue that we should also remove the spinlock in StartupXLOG and replace it with a write barrier. Obviously not for performance reasons, but because somebody might add more code to run under that spinlock. Looks good otherwise, although a read memory barrier ought to suffice. Greetings, Andres Freund -- Andres Freund http://www.2ndQuadrant.com/ PostgreSQL Development, 24x7 Support, Training & Services -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
