Tom Lane <t...@sss.pgh.pa.us> writes: > The point of the suggestion is to prove that the patch works as > advertised. How wide the sweet spot is for this test isn't nearly as > interesting as proving that there *is* a sweet spot. If you can't > find one it suggests that either the patch or the local posix_fadvise > doesn't work.
I posted tons of reproducible test cases with graphs of results for various raid stripe widths a while back. There was a very slight benefit on a single spindle at some prefetch depths but it wasn't very consistent and it varied heavily depending on the prefetch depth. I don't know what to make of this test. I don't know how to reproduce the same data distribution, I have no idea what raid configuration it's been run on, what version of what OS it's on, etc. It's quite possible posix_fadvise isn't working on it, I don't know. It's also possible the overhead of the extra buffer lookups and syscalls outweight any benefit of overlapping i/o and cpu on a single spindle. Trying to contrive a situation where a single spindle sees a significant benefit is going to be very tricky. Avoiding caching effects and the confounding effect of any overhead will make it hard to see a consistent benefit without a raid array. -- Gregory Stark EnterpriseDB http://www.enterprisedb.com Ask me about EnterpriseDB's 24x7 Postgres support! -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
