Re: Combining Aggregates

On Tue, Jan 19, 2016 at 4:50 PM, David Rowley
<david.rowley@2ndquadrant.com> wrote:
>> Oh, one more point: is there any reason why all of this needs to be a
>> single (giant) patch?  I feel like the handling of internal states
>> could be a separate patch from the basic patch to allow partial
>> aggregation and aggregate-combining, and that the latter could be
>> committed first if we had a reasonably final version of it.  That
>> seems like it would be easier from a review standpoint, and might
>> allow more development to proceed in parallel, too.
>
> I didn't ever really imagine that I'd include any actual new combinefns or
> serialfn/deserialfn in this patch. One set has of course now ended up in
> there, I can move these off to the test patch for now.
>
> Did you imagine that the first patch in the series would only add the
> aggcombinefn column to pg_aggregate and leave the aggserialfn stuff until
> later?

I think that would be a sensible way to proceed.

> I thought it seemed better to get the infrastructure committed in one
> hit, then add a bunch of new combinefn, serialfn, deserialfns for existing
> aggregates in follow-on commits.

To my mind, priority #1 ought to be putting this fine new
functionality to some use.  Expanding it to every aggregate we've got
seems like a distinctly second priority.  That's not to say that it's
absolutely gotta go down that way, but those would be my priorities.