Re: Improving avg performance for numeric

Hi Tom,

Tom Lane <tgl@sss.pgh.pa.us> wrote:
> After thinking about that for awhile: if we pursue this type of
> optimization, what would probably be appropriate is to add an aggregate
> property (stored in pg_aggregate) that allows direct specification of
> the size that the planner should assume for the aggregate's transition
> value.  We were getting away with a hardwired assumption of 8K for
> "internal" because the existing aggregates that used that transtype all
> had similar properties, but it was always really a band-aid not a proper
> solution.  A per-aggregate override could be useful in other cases too.

Cool.

I created a patch which adds an aggregate property to pg_aggregate, so
the transition space is can be overridden. This patch doesn't contain
the numeric optimizations. It uses "0" (meaning not-set) for all
existing aggregates.

I manual-tested it a bit, by changing this value for aggregates and
observing the changes in plan. I also updated some docs and pg_dump.

Does this look like something along the lines of what you meant?

Thanks,
  -- Hadi