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pg_dump and XID limit

From: Elliot Chance <elliotchance(at)gmail(dot)com>
To: pgsql-admin(at)postgresql(dot)org
Subject: pg_dump and XID limit
Date: 2010-11-24 02:18:28
Message-ID: DC1E3319-08CD-4C61-9565-06D744260261@gmail.com (view raw or flat)
Thread:
Lists: pgsql-admin
Hi,

This is a hypothetical problem but not an impossible situation. Just curious about what would happen.

Lets say you have an OLTP server that keeps very busy on a large database. In this large database you have one or more tables on super fast storage like a fusion IO card which is handling (for the sake of argument) 1 million transactions per second.

Even though only one or a few tables are using almost all of the IO, pg_dump has to export a consistent snapshot of all the tables to somewhere else every 24 hours. But because it's such a large dataset (or perhaps just network congestion) the daily backup takes 2 hours.

Heres the question, during that 2 hours more than 4 billion transactions could of occurred - so what's going to happen to your backup and/or database?

- Elliot

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