On Thu, Mar 24, 2011 at 12:36 PM, Jim Nasby <j...@nasby.net> wrote: > On Mar 23, 2011, at 5:12 PM, Tom Lane wrote: >> Robert Haas <robertmh...@gmail.com> writes: >>> It looks like the only way anything can ever get put on the free list >>> right now is if a relation or database is dropped. That doesn't seem >>> too good. >> >> Why not? AIUI the free list is only for buffers that are totally dead, >> ie contain no info that's possibly of interest to anybody. It is *not* >> meant to substitute for running the clock sweep when you have to discard >> a live buffer. > > Turns out we've had this discussion before: > http://archives.postgresql.org/pgsql-hackers/2010-12/msg01088.php and > http://archives.postgresql.org/pgsql-hackers/2010-12/msg00689.php > > Tom made the point in the first one that it might be good to proactively move > buffers to the freelist so that backends would normally just have to hit the > freelist and not run the sweep. > > Unfortunately I haven't yet been able to do any performance testing of any of > this... perhaps someone else can try and measure the amount of time spent by > backends running the clock sweep with different shared buffer sizes.
I tried under the circumstances I thought were mostly likely to show a time difference, and I was unable to detect a reliable difference in timing between free list and clock sweep. Cheers, Jeff -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
