From: | David Kerr <dmk(at)mr-paradox(dot)net> |
---|---|
To: | Greg Smith <greg(at)2ndquadrant(dot)com> |
Cc: | Scott Marlowe <scott(dot)marlowe(at)gmail(dot)com>, Nikolas Everett <nik9000(at)gmail(dot)com>, Robert Haas <robertmhaas(at)gmail(dot)com>, pgsql-performance(at)postgresql(dot)org |
Subject: | Re: Very high effective_cache_size == worse performance? |
Date: | 2010-04-20 20:39:19 |
Message-ID: | 20100420203919.GA62103@mr-paradox.net |
Views: | Raw Message | Whole Thread | Download mbox | Resend email |
Thread: | |
Lists: | pgsql-performance |
On Tue, Apr 20, 2010 at 04:26:52PM -0400, Greg Smith wrote:
- David Kerr wrote:
- >the db, xlog and logs are all on separate areas of the SAN.
- >separate I/O controllers, etc on the SAN. it's setup well, I wouldn't
- >expect
- >contention there.
- >
-
- Just because you don't expect it doesn't mean it's not there.
- Particularly something as complicated as a SAN setup, presuming anything
- without actually benchmarking it is a recipe for fuzzy diagnostics when
- problems pop up. If you took anyone's word that your SAN has good
- performance without confirming it yourself, that's a path that's lead
- many to trouble.
that's actually what I'm doing, performance testing this environment.
everything's on the table for me at this point.
- Anyway, as Robert already stated, effective_cache_size only impacts how
- some very specific types of queries are executed; that's it. If there's
- some sort of query behavior involved in your load, maybe that has
- something to do with your slowdown, but it doesn't explain general slow
- performance. Other possibilities include that something else changed
- when you reloaded the server as part of that, or it's a complete
- coincidence--perhaps autoanalyze happened to finish at around the same
- time and it lead to new plans.
Ok that's good to know. I didn't think it would have any impact, and was
surprised when it appeared to.
I just finished running the test on another machine and wasn't able to
reproduce the problem, so that's good news in some ways. But now i'm back
to the drawing board.
I don't think it's anything in the Db that's causing it. ( drop and re-create
the db between tests) I actually suspect a hardware issue somewhere.
Dave
From | Date | Subject | |
---|---|---|---|
Next Message | Dave Crooke | 2010-04-20 20:40:14 | Re: SOLVED ... Re: Getting rid of a cursor from JDBC .... Re: [PERFORM] Re: HELP: How to tame the 8.3.x JDBC driver with a biq guery result set |
Previous Message | Greg Smith | 2010-04-20 20:26:52 | Re: Very high effective_cache_size == worse performance? |