On Sun, Jan 19, 2014 at 5:57 AM, Andreas Karlsson <andr...@proxel.se> wrote:
> On 01/18/2014 08:13 PM, Jeremy Harris wrote: > >> On 31/12/13 01:41, Andreas Karlsson 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. >>> >> >> How does this work in combination with randomAccess ? >> > > As far as I can tell randomAccess was broken by the partial sort patch > even before my change since it would not iterate over multiple tuplesorts > anyway. > > Alexander: Is this true or am I missing something? Yes, I decided that Sort node shouldn't provide randomAccess in the case of skipCols !=0. See assert in the beginning of ExecInitSort. I decided that it would be better to add explicit materialize node rather than store extra tuples in tuplesortstate each time. I also adjusted ExecSupportsMarkRestore, ExecMaterializesOutput and ExecMaterializesOutput to make planner believe so. I found path->pathtype to be absolutely never T_Sort. Correct me if I'm wrong. Another changes in this version of patch: 1) Applied patch to don't compare skipCols in tuplesort by Marti Raudsepp 2) Adjusting sort bound after processing buckets. ------ With best regards, Alexander Korotkov.
partial-sort-6.patch.gz
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