On 16.1.2012 23:35, Greg Smith wrote: > On 01/12/2012 06:17 PM, Tomas Vondra wrote: >> I've run a series fo pgbench benchmarks with the aim to see the effect >> of moving the WAL logs to a separate drive, and one thing that really >> surprised me is that the archive log level seems to give much better >> performance than minimal log level. > > How repeatable is this? If you always run minimal first and then > archive, that might be the actual cause of the difference. In this > situation I would normally run this 12 times, with this sort of pattern: > > minimal > minimal > minimal > archive > archive > archive > minimal > minimal > minimal > archive > archive > archive > > To make sure the difference wasn't some variation on "gets slower after > each run". pgbench suffers a lot from problems in that class. AFAIK it's well repeatable - the primary goal of the benchmark was to see the benefir of moving the WAL to a separate device (with various WAL levels and device types - SSD and HDD). I plan to rerun the whole thing this week with a bit more details logged to rule out basic configuration mistakes etc. Each run is completely separate (rebuilt from scratch) and takes about 1 hour to complete. Each pgbench run consists of these steps 1) rebuild the data from scratch 2) 10-minute warmup (read-only run) 3) 20-minute read-only run 4) checkpoint 5) 20-minute read-write run and the results are very stable. Tomas -- Sent via pgsql-performance mailing list (pgsql-performance@xxxxxxxxxxxxxx) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-performance
