On Thu, Jun 6, 2013 at 3:01 AM, Amit Kapila <amit.kap...@huawei.com> wrote: > To avoid above 3 factors in test readings, I used below steps: > 1. Initialize the database with scale factor such that database size + > shared_buffers = RAM (shared_buffers = 1/4 of RAM). > For example: > Example -1 > if RAM = 128G, then initialize db with scale factor = 6700 > and shared_buffers = 32GB. > Database size (98 GB) + shared_buffers (32GB) = 130 (which > is approximately equal to total RAM) > Example -2 (this is based on your test m/c) > If RAM = 64GB, then initialize db with scale factor = 3400 > and shared_buffers = 16GB. > 2. reboot m/c > 3. Load all buffers with data (tables/indexes of pgbench) using pg_prewarm. > I had loaded 3 times, so that usage count of buffers will be approximately > 3.
Hmm. I don't think the usage count will actually end up being 3, though, because the amount of data you're loading is sized to 3/4 of RAM, and shared_buffers is just 1/4 of RAM, so I think that each run of pg_prewarm will end up turning over the entire cache and you'll never get any usage counts more than 1 this way. Am I confused? I wonder if it would be beneficial to test the case where the database size is just a little more than shared_buffers. I think that would lead to a situation where the usage counts are high most of the time, which - now that you mention it - seems like the sweet spot for this patch. -- Robert Haas EnterpriseDB: http://www.enterprisedb.com The Enterprise PostgreSQL Company -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
