Re: BUG #13750: Autovacuum slows down with large numbers of tables. More workers makes it slower.

On Fri, 30 Oct 2015 23:19:52 -0700
David Gould <daveg@sonic.net> wrote:

> The attached patch against REL9_5_STABLE_goes a little further. It
> claims the table under the lock, but also addresses the problem of all the
> workers racing to redo the same table by enforcing an ordering on all the
> workers. No worker can claim a table with an oid smaller than the highest
> oid claimed by any worker. That is, instead of racing to the same table,
> workers leapfrog over each other.
>
> In theory the recheck of the stats could be eliminated although this patch
> does not do that. It does eliminate the special handling of stats snapshots
> for autovacuum workers which cuts back on the excess rewriting of the stats
> file somewhat.
>
> I'll send numbers shortly, but as I recall it is over 100 times better than
> the original.

I sent performance test data and a setup for reproducing it elsewhere in
the thread. I also ran tests  on a larger system (128GB mem, many cores, 2x
SSD with battery backed raid).

This is for an idle system with 100,000 new small tables to analyze. I ran
all the test for an hour or 5000 tables processed. "jj" refers to the patch
from Jeff Janes, "dg" refers to the attached patch (same as previous).

/autovacuum actions per minute/
workers   9.5b1     jj     dg
-------   -----   ----  -----
   1        183    171    285
   4         45    212   1158
   8         23    462   1225


Could someone please take a look at the patch and comment? Thanks.

-dg

--
David Gould              510 282 0869         daveg@sonic.net
If simplicity worked, the world would be overrun with insects.