Re: pg_dump and XID limit

On 24/11/2010, at 5:07 PM, Tom Lane wrote:

> Elliot Chance <elliotchance(at)gmail(dot)com> writes:
>> 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?
>
> The DB will shut down to prevent wraparound once it gets 2 billion XIDs
> in front of the oldest open snaphot.
>
> regards, tom lane

Wouldn't that mean at some point it would be advisable to be using 64bit transaction IDs? Or would that change too much of the codebase?