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From: Elliot Chance <elliotchance@gmail.com>
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Subject: pg_dump and XID limit
Date: Wed, 24 Nov 2010 13:18:28 +1100
Message-Id: <DC1E3319-08CD-4C61-9565-06D744260261@gmail.com>
To: pgsql-admin@postgresql.org
Mime-Version: 1.0 (Apple Message framework v1081)

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=