On Tue, Dec 31, 2013 at 5:41 AM, Andreas Karlsson <andr...@proxel.se> wrote:
> On 12/29/2013 08:24 AM, David Rowley wrote: > >> If it was possible to devise some way to reuse any >> previous tuplesortstate perhaps just inventing a reset method which >> clears out tuples, then we could see performance exceed the standard >> seqscan -> sort. The code the way it is seems to lookup the sort >> functions from the syscache for each group then allocate some sort >> space, so quite a bit of time is also spent in palloc0() and pfree() >> >> If it was not possible to do this then maybe adding a cost to the number >> of sort groups would be better so that the optimization is skipped if >> there are too many sort groups. >> > > It should be possible. I have hacked a quick proof of concept for reusing > the tuplesort state. Can you try it and see if the performance regression > is fixed by this? > > One thing which have to be fixed with my patch is that we probably want to > close the tuplesort once we have returned the last tuple from ExecSort(). > > I have attached my patch and the incremental patch on Alexander's patch. Thanks. It's included into attached version of patch. As wall as estimation improvements, more comments and regression tests fix. ------ With best regards, Alexander Korotkov.
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