Ivan Voras wrote:
FWIW, yes - once the IO is fast enough or not necessary (e.g. the read-mostly database fits in RAM), RAM bandwidth *is* the next bottleneck and it really, really can be observed in actual loads.
This is exactly what I've concluded, after many rounds of correlating memory speed tests with pgbench tests against in-RAM databases. And it's the reason why I've written the stream-scaling utility and been collecting test results from as many systems as possible. That seemed to get dismissed upthread as not being the answer the poster was looking for, but I think you have to get a handle on that part before the rest of the trivia involved even matters.
I have a bunch more results that have been flowing in that I need to publish there soon. Note that there is a bug in stream-scaling where sufficiently large systems can hit a compiler problem where it reports "relocation truncated to fit: R_X86_64_PC32 against `.bss'". I have two of those reports and am working on resolving.
-- Greg Smith 2ndQuadrant US greg@xxxxxxxxxxxxxxx Baltimore, MD PostgreSQL Training, Services and Support www.2ndQuadrant.us "PostgreSQL 9.0 High Performance": http://www.2ndQuadrant.com/books -- Sent via pgsql-performance mailing list (pgsql-performance@xxxxxxxxxxxxxx) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-performance
