Date: Wed, 9 Jan 2013 22:31:19 +0800 (SGT) From: Patrick Dung <patrick_dkt@yahoo.com.hk> To: freebsd-fs@freebsd.org Subject: ZFS sub-optimal performance with default setting Message-ID: <1357741879.56011.YahooMailClassic@web190806.mail.sg3.yahoo.com>
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Hi freebsd-fs! I have my the original question in: http://archives.postgresql.org/pgsql-performance/2013-01/msg00044.php But later it was found out the bottleneck seems to be the ZFS with out a fa= st ZIL. Please give some advise, thanks. Details: Postgresql 9.2.2 (complied by gcc) is installed in FreeBSD 9.1 i386. The pgsql base directory is in a ZFS dataset. I have noticed the performance is sub-optimal, but I know the default=20 setting should be the most safest one to be use (concern about data integri= ty). a) I use OTRS ticketing system version 3.1, the backend is PostgreSQL. The user interactive response is not slow (switching web pages or create a = change). b) There is a benchmark in the support module of OTRS. It tested insert,update,select and delete performance. The response time is slow (>10 sec), except select. I have done some research on web, with below settings (just one change, not= both), the performance returned to normal: 1) Disabled sync in the pgsql dataset in ZFS zfs set sync=3Ddisabled mydata/pgsql or=20 2) In =A0postgresql.conf, set synchronous_commit from on to off I know the above setting would lead to data loss (e.g.power goes off), any = comments? PS: 1) I have tried to use primarycache/secondarycache=3Dmetadata/none, it do n= ot seem to help. 2) I have tried the default setting on Linux too: RHEL 6.3, ext4, stock postgresql 8.x, OTRS 3.1. The web site is responsive and the benchmark result is more or less the sam= e as FreeBSD with the 'sync' turned off. 3) For FreeBSD, same setting with Postgresql on UFS: The performance is between ZFS (default, sync enabled) and ZFS (sync disabl= ed). Thanks, Patrick
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