pg_dump and XID limit

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
tableson super fast storage like a fusion IO card which is handling (for the sake of argument) 1 million transactions
persecond. 

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
thetables to somewhere else every 24 hours. But because it's such a large dataset (or perhaps just network congestion)
thedaily 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
toyour backup and/or database? 

- Elliot