Bruce Momjian <pgman@candle.pha.pa.us> writes:
> Have you considered having the background writer check the pages it is
> about to write to see if they can be added to the FSM, thereby reducing
> the need for vacuum? Seems we would need to add a statistics parameter
> so pg_autovacuum would know how many tuples the background write added
> to the freespace map, so it doesn't vacuum a table that doesn't need it.
This would suffer from the previously mentioned problem of having to pull in
index pages and dirty them when it's trying to flush and clean pages.
Conceivably it could just count up the dead tuples and provide that
information to something like pg_autovacuum so it knows when it's time to run
a vacuum. I don't see that as all that much of a win over the current
heuristics. At best it means a big batch update will trigger a vacuum sooner
so you don't have to manually run vacuum to avoid overflowing the fsm.
--
greg