Re: pgsql: Teach tuplesort.c about "top N" sorting, in which only the first

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Gregory Stark wrote:
>
> "Tom Lane" <tgl(at)sss(dot)pgh(dot)pa(dot)us> writes:
>
> > Magnus Hagander <magnus(at)hagander(dot)net> writes:
> >> Could we show it in EXPLAIN ANALYZE somehow? I'm thinking it would be good
> >> to see at runtime (for example as a hint that if you put in a bit more
> >> work_mem it might get used)
> >
> > I don't see that this is any more interesting than whether the sort
> > spilled to disk or not; which is something we don't show in EXPLAIN
> > ANALYZE either. trace_sort is the agreed API for examining that.
> > It's not exactly easy to do, because (a) none of this information
> > is exposed outside tuplesort.c, and (b) the tuplesortstate object
> > is probably gone by the time EXPLAIN ANALYZE runs, anyway.
>
> It would be positively wonderful to see whether the sort spilled to disk in
> the explain analyze. Could we make putting more feedback about sorts in
> EXPLAIN ANALYZE output a TODO?
>
> --
> Gregory Stark
> EnterpriseDB http://www.enterprisedb.com
>
>
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