Re: autovacuum

> This seems maybe a bit overkill to me. I think what would be more useful
> is if autovacuum could execute more than one vacuum at a time, and you
> could specify tables that are high priority (or possibly just say that
> all tables with less than X live tuples in them are high priority). That
> way a longer-running vacuum on a large table wouldn't prevent more
> vacuum-sensative tables (such as queues) from being vacuumed frequently
> enough.

Actually, I can think of a case for much the opposite, namely to want
to concurrently vacuum some LARGE tables...

Suppose you have 2 rather big tables that get updates on similar
schedules such that both will have a lot of dead tuples at similar
times.

And suppose both of these tables are Way Large, so that they take
six hours to vacuum.

I could argue for kicking off vacuums on both, at the same moment;
they'll both be occupying transactions for 1/4 of a day, and, with
possibly related patterns of updates, doing them one after the other
*wouldn't* forcibly get you more tuples cleaned than doing them
concurrently.

I'm not sure that's a case to push for, either, as something
pg_autovacuum is smart enough to handle; I'm just putting out some
ideas that got enough internal discussion to suggest they were
interesting enough to let others consider...
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