Excerpts from Robert Haas's message of mar jun 21 09:40:16 -0400 2011: > On Mon, Jun 20, 2011 at 6:55 PM, Simon Riggs <si...@2ndquadrant.com> wrote: > > I agree the scope for RELOID errors increased with my 9.1 patch. I'm > > now happy with the locking patch (attached), which significantly > > reduces the scope - back to the original error scope, in my testing. > > > > I tried to solve both, but I think that's a step too far given the timing. > > > > It seems likely that there will be objections to this patch. All I > > would say is that issuing a stream of ALTER TABLEs against the same > > table is not a common situation; if it were we would have seen more of > > the pre-existing bug. ALTER TABLE command encompasses many subcommands > > and we should evaluate each subcommand differently when we decide what > > to do. > > Well, my principal objection is that I think heavyweight locking is an > excessively expensive solution to this problem. I think the patch is > simple enough that I wouldn't object to applying it on those grounds > even at this late date, but I bet if we do some benchmarking on the > right workload we'll find a significant performance regression.
Yeah, taking a hw lock at each relcache item build is likely to be prohibitively expensive. Heck, relation extension is expensive already in some loads. (I'm guessing that things will tank when there's a relcache reset). Still, this seems to be an overall better approach to the problem than what's been proposed elsewhere. Maybe we can do something with a map of relations that are protected by a bunch of lwlocks instead. (We could use that for relation extension too; that'd rock.) The patch may be simple, but is it complete? I think you need to have lock acquisition on create rule and create index too. Right now it only has locks on trigger stuff and alter table. -- Álvaro Herrera <alvhe...@commandprompt.com> The PostgreSQL Company - Command Prompt, Inc. PostgreSQL Replication, Consulting, Custom Development, 24x7 support -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
