Re: How to diagnose application "hangs" in pg_receive?

From: Clemens Eisserer <linuxhippy(at)gmail(dot)com>
To: pgsql-jdbc(at)postgresql(dot)org
Subject: Re: How to diagnose application "hangs" in pg_receive?
Date: 2011-05-21 18:35:45
Message-ID: BANLkTi=LLpnGZOsyHQFnYvpAe1C7T8+HUQ@mail.gmail.com
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Hi Kevin,

If you feel personally attacked, just because I highlighted that I am
sure the problem is not caused by a query taking a long time to
execute, I am sorry. Nontheless, please find my detailed answers
below.

Thanks, Clemens

> You haven't told us what version of PostgreSQL you're running,
PostgreSQL 8.4.7
postgresql-8.4-701.jdbc3.jar

> spite of my asking that you post the results of a query which would
> have told us that and other useful information.
Because as I said, the problem is not the execution of the query.
Last time I experienced such a hang it was a simple "select .... from
... where id=x" query, which executes usually in a few ms.

> The only evidence that you have provided suggests that at
> least part of your problem has been bloat, but you dismissed that
> out of hand without showing any sign that you understand that issue
> or have checked for it.
The database has about 2MB of data stored and is mostly read-only.
I know what bloat is, understand the issue and have given a clear
indication that I know bloat is not the problem.
Therefor narrowing down the possibilities, and to direct guessing into
another direction.

> In follow-ups, please try to avoid hand-wavy terms like "forever";
> tell us whether you waited a minute, an hour, ten days, whatever
> "forever" actually was, along with any observations on CPU and disk
> usage during this time.  You didn't show the active query in your
> listings -- were those taking during the time the query was hanging?

Forever means, what forever usually means - as long as I terminate the client.
I took this hand-wavy term to make clear that my understanding of the
problem is that its not a slowly running query.

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