Added to TODO: * Test to see if calling PreallocXlogFiles() from the background writer will help with WAL segment creation latency
http://archives.postgresql.org/pgsql-patches/2007-06/msg00340.php --------------------------------------------------------------------------- Tom Lane wrote: > Heikki Linnakangas <[EMAIL PROTECTED]> writes: > > Here's latest revision of Itagaki-sans Load Distributed Checkpoints patch: > > Applied with some minor revisions to make some of the internal APIs a > bit cleaner; mostly, it seemed like a good idea to replace all those > bool parameters with a flag-bits approach, so that you could have > something like "CHECKPOINT_FORCE | CHECKPOINT_WAIT" instead of > "false, true, true, false" ... > > For the moment I removed all the debugging elog's in the patch. > We still have Greg Smith's checkpoint logging patch to look at > (which I suppose needs adjustment now), and that seems like the > appropriate venue to consider what to put in. > > Also, the question of redesigning the bgwriter's LRU scan is > still open. I believe that's on Greg's plate, too. > > One other closely connected item that might be worth looking at is the > code for creating new future xlog segments (PreallocXlogFiles). Greg > was griping upthread about xlog segment creation being a real > performance drag. I realized that as we currently have it set up, the > checkpoint code is next to useless for high-WAL-volume installations, > because it only considers making *one* future XLOG segment. Once you've > built up enough XLOG segments, the system isn't too bad about recycling > them, but there will be a nasty startup transient where foreground > processes have to stop and make the things. I wonder whether it would > help if we (a) have the bgwriter call PreallocXlogFiles during its > normal loop, and (b) back the slop in PreallocXlogFiles way off, so that > it will make a future segment as soon as we start using the last > existing segment, instead of only when we're nearly done. This would at > least make it more likely that the bgwriter does the work instead of a > foreground process. I'm hesitant to go much further than that, because > I don't want to bloat the minimum disk footprint for low-volume > installations, but the minimum footprint is really 2 xlog files anyway... > > regards, tom lane > > ---------------------------(end of broadcast)--------------------------- > TIP 4: Have you searched our list archives? > > http://archives.postgresql.org -- Bruce Momjian <[EMAIL PROTECTED]> http://momjian.us EnterpriseDB http://postgres.enterprisedb.com + If your life is a hard drive, Christ can be your backup. + -- Sent via pgsql-patches mailing list (pgsql-patches@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-patches
