* Havasvölgyi Ottó: > 2011/12/19 Florian Weimer <fweimer@xxxxxx> > >> * Havasvölgyi Ottó: >> >> > Even though the TPS in pgbench about 700 with 1 client. >> > I have tried other sync methods (fdatasync, open_sync), but all are >> similar. >> > Should I disable write cache on HDD to make it work? >> >> Did you mount your ext4 file system with the nobarrier option? >> >> By default, ext4 is supposed to cope properly with hard disk caches, >> unless the drive is lying about completing writes (but in that case, >> disabling write caching is probably not going to help much with >> reliability, either). >> > > It is mounted with defaults, no other option yet, so it should flush. > These HDDs are 7200 rpm SATA with some low level software RAID1. > I cannot understand why disabling HDD write cache does not help either. > Could you explain please? The drive appears to be fundamentally broken. Disabling the cache won't change that. But you mention software RAID1---perhaps your version of the RAID code doesn't pass down the barriers to the disk? > There is also an InnoDB transaction log on this partition, but its commit > time is quite longer. On the same workload PgSql's commit is about 1 ms, > but InnoDB's is about 4-7 ms. I think 4-7 is also too short to flush > something to such disk, am I right? Yes, it's still too low, unless multiple commits are grouped together. -- Florian Weimer <fweimer@xxxxxx> BFK edv-consulting GmbH http://www.bfk.de/ Kriegsstraße 100 tel: +49-721-96201-1 D-76133 Karlsruhe fax: +49-721-96201-99 -- Sent via pgsql-general mailing list (pgsql-general@xxxxxxxxxxxxxx) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-general
