On 1/27/2011 4:31 AM, Michael Kohl wrote:
Hi all,
we are running a fairly big Ruby on Rails application on Postgres 8.4.
Our traffic grew quite a bit lately, and since then we are facing DB
performance issues. System load occasionally explodes (around 170
yesterday on a 16 core system), which seems to be caused by disk I/O
(iowait in our Munin graphs goes up significantly during these
periods). At other times the laod stays rather low under pretty much
the same circumstances.
There are 6 application servers with 18 unicorns each, as well as 12
beanstalk workers talking to the DB. I know the problem description is
very vague, but so far we haven't consistently managed to reproduce
the problem. Turning of the beanstalk workers usually leads to a great
decreases in writes and system loads, but during yesterday's debugging
session they obviously ran fine (thanks, Murphy).
Below you'll find our system information and Postgres config, maybe
someone could be so kind as to point out any obvious flaws in our
current configuration while I'm trying to get a better description of
the underlying problem.
<SNIP>
If the suggestions below are not enough, you might have to check some of
your sql statements and make sure they are all behaving. You may not
notice a table scan when the user count is low, but you will when it
gets higher.
Have you run each of your queries through explain analyze lately?
Have you checked for bloat?
You are vacuuming/autovacuuming, correct?
-Andy
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