Re: Chronic performance issue with Replication Failover and FSM.

From: Heikki Linnakangas <heikki(dot)linnakangas(at)enterprisedb(dot)com>
To: Josh Berkus <josh(at)agliodbs(dot)com>
Cc: PostgreSQL-development <pgsql-hackers(at)postgreSQL(dot)org>
Subject: Re: Chronic performance issue with Replication Failover and FSM.
Date: 2012-03-14 07:16:32
Message-ID: 4F6045D0.6020403@enterprisedb.com
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On 14.03.2012 01:53, Josh Berkus wrote:
> 1. The Free Space Map is not replicated between servers.
>
> 2. Thus, when we fail over to a replica, it starts with a blank FSM.

The FSM is included in the base backup, and it is updated when VACUUM
records are replayed.

It is also updated when insert/update/delete records are replayed,
athough there's some fuzziness there: records with full page images
don't update the FSM, and the FSM is only updated when the page has less
than 20% of free space left. But that would cause an error in the other
direction, with the FSM claiming that some pages have more free space
than they do in reality.

--
Heikki Linnakangas
EnterpriseDB http://www.enterprisedb.com

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