Autovacuum question

I have a postgres 8.x database that appears to be append only. Do I any need to run autovacuum or should I refrain from using it?

Thanks.

First: 8.3 and older are no longer supported.
8.4 will only be supported until the end of this year. So you should consider upgrading as soon as possible

9.x has many new features and a lot of performance improvements so it will pay off if you update.

Now to your original question: you should never disable autovacuum.

Disabling it has no advantages but keeping it running will have (e.g. your statistics will be updated).