Simon Riggs wrote: > On Wed, 2009-10-21 at 23:02 +0300, Heikki Linnakangas wrote: >> Hmm, dunno about that, but there is one problem with the "grant to dummy >> proc, then release in startup process" approach. What if there isn't >> enough shared memory available to re-acquire the lock for the dummy >> proc? It would be rather unfortunate to throw an error and shut down the >> standby, instead of promoting it to a new master. > > Any error would be unfortunate at that point. That particular error > seems unlikely, since we are only talking about AccessExclusiveLocks. If > the server has a problem with that many locks, then it is severely in > danger from prepared transactions in the general case, since such errors > could be also be thrown by the current code in mildly different > circumstances.
Note that read-only backends also occupy lock space when they run queries, taking AccessShareLocks. > Do you see any alternative approaches to the one taken? Making some effort to transfer locks instead of acquiring+releasing would eliminate the need for having extra lock space available when switching from hot standby mode to normal operation. >> In fact, what happens if you ran out of shared memory when replaying a >> relation_redo_lock record? Panic? > > An ERROR in the startup process will cause it to upgrade to FATAL, > AFAIK. That means the server will do a crash shutdown, AIUI. That is the > equivalent of a PANIC, I guess. How else could it behave? It could wait for backends to release locks. If there isn't any, then you don't have much choice. -- Heikki Linnakangas EnterpriseDB http://www.enterprisedb.com -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
