Excerpts from Robert Haas's message of mié may 02 08:14:36 -0400 2012: > On Wed, May 2, 2012 at 7:16 AM, Jeroen Vermeulen <j...@xs4all.nl> wrote: > > On 2012-05-01 22:06, Robert Haas wrote: > >> It might also be interesting to provide a mechanism to pre-extend a > >> relation to a certain number of blocks, though if we did that we'd > >> have to make sure that autovac got the memo not to truncate those > >> pages away again. > > > > Good point. And just to check before skipping over it, do we know that > > autovacuum not leaving enough slack space is not a significant cause of the > > bottlenecks in the first place? > > I'm not sure exactly what you mean by this: autovacuum doesn't need > any slack space. Regular DML operations can certainly benefit from > slack space, both within each page and overall within the relation. > But there's no evidence that vacuum is doing too good a job cleaning > up the mess, forcing the relation to be re-extended. Rather, the > usual (and frequent) complaint is that vacuum is leaving way too much > slack space - i.e. bloat.
Hm. I see those two things as different -- to me, bloat is unremoved dead tuples, whereas slack space would be free space that can be reused by new tuples. Slack space is useful as it avoids relation extension; bloat is not. I wonder, though, if we should set a less-than-100 fillfactor for heap relations. Just like default_statistic_target, it seems that the default value should be a conservative tradeoff between two extremes. This doesn't help extension for bulk insertions a lot, of course, but it'd be useful for tables where HOT updates happen with some regularity. -- 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
