Re: 9.5: Memory-bounded HashAgg
От | Jeff Davis |
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Тема | Re: 9.5: Memory-bounded HashAgg |
Дата | |
Msg-id | 1408434765.2335.206.camel@jeff-desktop обсуждение исходный текст |
Ответ на | Re: 9.5: Memory-bounded HashAgg (Robert Haas <robertmhaas@gmail.com>) |
Ответы |
Re: 9.5: Memory-bounded HashAgg
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Список | pgsql-hackers |
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". 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[1] (particularly useful for parallelism)? Both of those discussions are worth having, and perhaps they can happen in parallel as I wrap up this patch. 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. Regards,Jeff Davis [1] http://blogs.msdn.com/b/craigfr/archive/2008/01/18/partial-aggregation.aspx
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