> -----Original Message----- > From: pgsql-hackers-ow...@postgresql.org [mailto:pgsql-hackers- > ow...@postgresql.org] On Behalf Of Tom Lane > But really there are two different performance regimes here, one where > the hash data is large enough to spill to disk and one where it isn't. > Reducing work_mem will cause data to spill into kernel disk cache, but > if the total problem fits in RAM then very possibly that data won't ever > really go to disk. So I suspect such a test case will act more like the > small-data case than the big-data case. You probably actually need more > data than RAM to be sure you're testing the big-data case.
Is there a way to limit the kernel disk cache? (We are running SUSE Linux.) We have been testing hybrid hash join performance and have seen that the performance varies considerably less than expected even for dramatic changes in work_mem and the I/Os that appear to be performed. -- Ramon Lawrence -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
