Date: Thu, 13 Aug 2015 20:24:28 +0000 (UTC)
From: Kevin Grittner <kgrittn@ymail.com>
Reply-To: Kevin Grittner <kgrittn@ymail.com>
To: Josh Berkus <josh@agliodbs.com>,
 "pgsql-performance@postgresql.org" <pgsql-performance@postgresql.org>
Message-ID: <512125623.2442595.1439497468170.JavaMail.yahoo@mail.yahoo.com>
In-Reply-To: <55CCCF4A.2080102@agliodbs.com>
References: <55CCCF4A.2080102@agliodbs.com>
Subject: Re: Strange query stalls on replica in 9.3.9
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Josh Berkus <josh@agliodbs.com> wrote:

> Periodically the master runs an "update all rows" query on the main
> table in the database.  When this update hits the replica via
> replication stream, *some* (about 5%) of the queries which do seq scans
> will stall for 22 to 32 seconds (these queries normally take about
> 75ms).  Queries which do index scans seem not to be affected.
>
> Thing is, the update all rows only takes 2.5 seconds to execute on the
> master. So even if the update is blocking the seq scans on the replica
> (and I can't see why it would), it should only block them for < 3 seconds.

Visibility hinting and/or hot pruning?

--
Kevin Grittner
EDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company


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