From: Josh Berkus <josh@agliodbs.com>
To: pgsql-performance@postgresql.org
Subject: Strange query stalls on replica in 9.3.9
Date: Thu, 13 Aug 2015 10:09:30 -0700
Message-ID: <55CCCF4A.2080102@agliodbs.com> (raw)
List-Unsubscribe: <mailto:majordomo@postgresql.org?body=unsub%20pgsql-performance>
Setup:
* PostgreSQL 9.3.9
* 1 master, 1 replica
* Tiny database, under 0.5GB, completely cached in shared_buffers
* 90% read query traffic, which is handled by replica
* Traffic in the 1000's QPS.
The wierdness:
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.
Anyone seen anything like this?
--
Josh Berkus
PostgreSQL Experts Inc.
http://pgexperts.com
--
Sent via pgsql-performance mailing list (pgsql-performance@postgresql.org)
To make changes to your subscription:
http://www.postgresql.org/mailpref/pgsql-performance
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Reply to all the recipients using the --to and --cc options:
reply via email
To: pgsql-performance@postgresql.org
Cc: josh@agliodbs.com
Subject: Re: Strange query stalls on replica in 9.3.9
In-Reply-To: <55CCCF4A.2080102@agliodbs.com>
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
This inbox is served by DDX for PostgreSQL; see mirroring instructions
for how to clone and mirror all data and code used for this inbox