On 19 Srpen 2014, 9:52, Jeff Davis wrote: > On Fri, 2014-08-15 at 13:53 -0400, Robert Haas wrote: >> I think that's right, and I rather like your (Jeff's) approach. It's >> definitely true that we could do better if we have a mechanism for >> serializing and deserializing group states, but (1) I think an awful >> lot of cases would get an awful lot better even just with the approach >> proposed here and (2) I doubt we would make the >> serialization/deserialization interfaces mandatory, so even if we had >> that we'd probably want a fallback strategy anyway. > > Thank you for taking a look. > > To solve the problem for array_agg, that would open up two potentially > lengthy discussions: > > 1. Trying to support non-serialized representations (like > ArrayBuildState for array_agg) as a real type rather than using > "internal".
That's certainly an option, and it's quite straightforward. The downside of it is that you either prevent the aggregates from using the most efficient state form (e.g. the array_agg might use a simple array as a state) or you cause a proliferation of types with no other purpose. > 2. What changes should we make to the aggregate API? As long as we're > changing/extending it, should we go the whole way and support partial > aggregation (particularly useful for parallelism)? Maybe, but not in this patch please. That's far wider scope, and while considering it when designing API changes is probably a good idea, we should resist the attempt to do those two things in the same patch. > Both of those discussions are worth having, and perhaps they can happen > in parallel as I wrap up this patch. Exactly. > I'll see whether I can get consensus that my approach is (potentially) > commit-worthy, and your statement that it (potentially) solves a real > problem is a big help. IMHO it's a step in the right direction. It may not go as far as I'd like, but that's OK. regards Tomas -- Sent via pgsql-hackers mailing list (firstname.lastname@example.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers