Hi all, 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. On spinning drives this is not noticeable, but on SSDs it's quite clear. See for example this: http://www.fuzzy.cz/tmp/tps-rw-minimal.png http://www.fuzzy.cz/tmp/tps-rw-archive.png That minimal log level gives about 1600 tps all the time, while archive log level gives about the same performance at the start but then it continuously increases up to about 2000 tps. This seems very suspicious, because AFAIK the wal level should not really matter for pgbench and if it does I'd expect exactly the opposite behaviour (i.e. 'archive' performing worse than 'minimal'). This was run on 9.1.2 with two SSDs (Intel 320) and EXT4, but I do see exactly the same behaviour with a single SSD drive. The config files are here (the only difference is the wal_level line at the very end) http://www.fuzzy.cz/tmp/postgresql-minimal.conf http://www.fuzzy.cz/tmp/postgresql-archive.conf pgbench results and logs are here: http://www.fuzzy.cz/tmp/pgbench.minimal.log.gz http://www.fuzzy.cz/tmp/pgbench.archive.log.gz http://www.fuzzy.cz/tmp/results.minimal.log http://www.fuzzy.cz/tmp/results.archive.log I do plan to rerun the whole benchmark, but is there any reasonable explanation or something that might cause such behaviour? kind regards Tomas -- Sent via pgsql-performance mailing list (pgsql-performance@xxxxxxxxxxxxxx) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-performance
