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Re: Update performance degrades over time

From: "Jeffrey Baker" <jwbaker(at)gmail(dot)com>
To: "Subbiah Stalin-XCGF84" <SSubbiah(at)motorola(dot)com>, "pgsql-performance(at)postgresql(dot)org" <pgsql-performance(at)postgresql(dot)org>
Subject: Re: Update performance degrades over time
Date: 2008-05-15 13:56:24
Message-ID: fd145f7d0805150656n4c0a61aes810b12d72ea3765a@mail.gmail.com (view raw or flat)
Thread:
Lists: pgsql-performance
On Wed, May 14, 2008 at 6:31 PM, Subbiah Stalin-XCGF84
<SSubbiah(at)motorola(dot)com> wrote:
> Hi All,
>
> We are doing some load tests with our application running postgres 8.2.4. At
> times we see updates on a table taking longer (around
> 11-16secs) than expected sub-second response time. The table in question is
> getting updated constantly through the load tests. In checking the table
> size including indexes, they seem to be bloated got it confirmed after
> recreating it (stats below). We have autovacuum enabled with default
> parameters. I thought autovaccum would avoid bloating issues but looks like
> its not aggressive enough. Wondering if table/index bloating is causing
> update slowness in over a period of time. Any ideas how to troubleshoot this
> further.

Sometimes it is necessary to not only VACUUM, but also REINDEX.  If
your update changes an indexed column to a new, distinct value, you
can easily get index bloat.

Also, you should check to see if you have any old, open transactions
on the same instance.  If you do, it's possible that VACUUM will have
no beneficial effect.

-jwb

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