Re: Autovacuum Improvements

On Mon, 2007-01-08 at 22:29, Chris Browne wrote:
[snip]
> Based on the three policies I've seen, it could make sense to assign
> worker policies:
>
> 1. You have a worker that moves its way through the queue in some sort of
>    sequential order, based on when the table is added to the queue, to
>    guarantee that all tables get processed, eventually.
>
> 2. You have workers that always pull the "cheapest" tables in the
>    queue, perhaps with some sort of upper threshold that they won't go
>    past.
>
> 3. You have workers that alternate between eating from the two ends of the
>    queue.
>
> Only one queue is needed, and there's only one size parameter
> involved.
> Having multiple workers of type #2 seems to me to solve the problem
> you're concerned about.

This sounds better, but define "cheapest" in #2... I actually want to
continuously vacuum tables which are small, heavily recycled
(insert/update/delete), and which would bloat quickly. So how do you
define the cost function for having these tables the "cheapest" ?

And how will you define the worker thread count policy ? Always 1 worker
per category, or you can define the number of threads in the 3
categories ? Or you still have in mind time window policies with allowed
number of threads per worker category ? (those numbers could be 0 to
disable a a worker category).

Other thing, how will the vacuum queue be populated ? Or the "queue" here means nothing, all workers will always go
throughall tables to pick one based on their own criteria ? My concern here is that the current way of checking 1 DB
perminute is not going to work with category #2 tables, they really have to be vacuumed continuously sometimes. 

Cheers,
Csaba.