Thanks a lot for the detailed reply. Matthew Wakeling: > On Thu, 14 Jan 2010, fkater@xxxxxxxxxxxxxx wrote: > > This takes about 50s, so, 800MB/50s = 16MB/s. > > > > However the harddisk (sata) could write 43 MB/s in the worst > > case! Why is write performance limited to 16 MB/s? > > Several reasons: > > The data needs to be written first to the WAL, in order to provide > crash-safety. So you're actually writing 1600MB, not 800. I understand. So the actual throughput is 32MB/s which is closer to 43 MB/s, of course. Can I verify that by temporarily disabling WAL writes completely and see if the thoughput is then doubled? Felix -- Sent via pgsql-performance mailing list (pgsql-performance@xxxxxxxxxxxxxx) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-performance
