Postgres assumes that the OS takes care of caching: "PLEASE NOTE. PostgreSQL counts a lot on the OS to cache data files and hence does not bother with duplicating its file caching effort. The shared buffers parameter assumes that OS is going to cache a lot of files and hence it is generally very low compared with system RAM. Even for a dataset in excess of 20GB, a setting of 128MB may be too much, if you have only 1GB RAM and an aggressive-at-caching OS like Linux." Tuning PostgreSQL for performance, Shridhar Daithankar, Josh Berkus, 2003, http://www.varlena.com/GeneralBits/Tidbits/perf.html
Slightly off-topic, I have noticed at least 25% performance gain on my postgresql database after installing Wu Fengguang's adaptive read- ahead disk cache patch for the linux kernel. http://lkml.org/lkml/ 2005/9/15/185 http://www.samag.com/documents/s=10101/sam0616a/0616a.htm I was wondering if Solaris uses a similar approach. On 04/10/2007, at 4:44 AM, Dale Ghent wrote: > On Oct 3, 2007, at 5:21 PM, Richard Elling wrote: > > >> Slightly off-topic, in looking at some field data this morning >> (looking >> for something completely unrelated) I notice that the use of directio >> on UFS is declining over time. I'm not sure what that means... >> hopefully >> not more performance escalations... >> > > Sounds like someone from ZFS team needs to get with someone from > Oracle/MySQL/Postgres and get the skinny on how the IO rubber->road > boundary should look, because it doesn't sound like there's a > definitive or at least a sure answer here. > > Oracle trumpets the use of DIO, and there are benchmarks and first- > hand accounts out there from DBAs on its virtues - at least when > running on UFS (and EXT2/3 on Linux, etc) > > As it relates to ZFS mechanics specifically, there doesn't appear to > be any settled opinion. > > /dale > _______________________________________________ > zfs-discuss mailing list > zfs-discuss@opensolaris.org > http://mail.opensolaris.org/mailman/listinfo/zfs-discuss _______________________________________________ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
