Re: [HACKERS] Runtime Partition Pruning

On 22 December 2017 at 14:29, Robert Haas <robertmhaas(at)gmail(dot)com> wrote:
> On Thu, Dec 21, 2017 at 6:53 PM, David Rowley
> <david(dot)rowley(at)2ndquadrant(dot)com> wrote:
>> Are you considering some sort of clauselist_selectivity() estimate on
>> the given parameters and comparing that to the same selectivities that
>> were determined for the previous custom plans?
>
> No, I don't think comparing to previous custom plans is a workable
> approach. I was thinking, rather, that if we know for example that
> we've doing pruning on partition_column = $1, then we know that only
> one partition will match. That's probably a common case. If we've
> got partition_column > $1, we could assume that, say, 75% of the
> partitions would match. partition_column BETWEEN $1 and $2 is
> probably a bit more selective, so maybe we assume 50% of the
> partitions would match.

Okay. Do you think this is something we need to solve for this patch?
When I complained originally I didn't quite see any way to even test
the majority of this patch with the regression tests, but Beena has
since proven me wrong about that.

--
David Rowley http://www.2ndQuadrant.com/
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