Re: PATCH: Split stats file per database WAS: autovacuum stress-testing our system

Hi,

just a few charts from our production system, illustrating the impact of
this patch. We've deployed this patch on January 12 on our systems
running 9.1 (i.e. a backpatch), so we do have enough data to do some
nice pics from it. I don't expect the changes made to the patch since
then to affect the impact significantly.

I've chosen two systems with large numbers of databases (over 1000 on
each), each database contains multiple (possibly hundreds or more).

The "cpu" first charts show quantiles of CPU usage, and assuming that
the system usage did not change, there's a clear drop by about 15%
percent in both cases. This is a 8-core system (on AWS), so this means a
save of about 120% of one core.

The "disk usage" charts show how much space was needed for the stats
(placed on tmpfs filesystem, mounted at /mnt/pg_tmp). The filesystem max
size is 400MB and the files require ~100MB. With the unpatched code the
space required was actually ~200MB because of the copying.

regards
Tomas