Jim C. Nasby wrote:
On Thu, Aug 17, 2006 at 03:00:00PM +0900, ITAGAKI Takahiro wrote:
IMO, the only reason at all for naptime is because there is a
non-trivial cost associated with checking a database to see if any
vacuuming is needed.
This cost is reduced significantly in the integrated version as compared
to the contrib version, but yes still not zero.
One problem that I've run across is that in a cluster with a lot of
databases it can take a very long time to cycle through all of them.
Perhaps a better idea would be to check a number of databases on each
pass. That way you won't bog the server down while checking, but it
won't take as long to get to all the databases.
Also, autovac should immediately continue checking databases after it
finishes vacuuming one. The reason for this is that while vacuuming,
the vacuum_cost_delay settings will almost certainly be in effect, which
will prevent autovac from hammering the system. Since the system won't
be hammered during the vacuum, it's ok to check more databases
immediately after finishing vacuuming on one.
This is basically what Itagaki's patch does.
Does anyone have any info on how much load there actually is when
checking databases to see if they need vacuuming?
I haven't.
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