Horton

Re: why partition pruning doesn't work?

David Rowley <david.rowley@2ndquadrant.com>

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From: David Rowley <david.rowley@2ndquadrant.com>
To: Tom Lane <tgl@sss.pgh.pa.us>
Cc: Amit Langote <Langote_Amit_f8@lab.ntt.co.jp>, Dmitry Dolgov <9erthalion6@gmail.com>, Jeff Janes <jeff.janes@gmail.com>, Ashutosh Bapat <ashutosh.bapat@enterprisedb.com>, Pavel Stehule <pavel.stehule@gmail.com>, PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>
Date: 2018-06-08T06:14:00Z
Lists: pgsql-hackers 
On 8 June 2018 at 15:22, Tom Lane <tgl@sss.pgh.pa.us> wrote:
> David Rowley <david.rowley@2ndquadrant.com> writes:
>> On 8 June 2018 at 03:43, Tom Lane <tgl@sss.pgh.pa.us> wrote:
>>> Maybe there's something I'm missing here, but I sort of hoped that this
>>> patch would nuke all the special-case code for Params in this area.
>>> Why is there any need to distinguish them from other stable expressions?
>
>> We need to know which Params exist in the Expr as if there are no
>> Params, or only external Params, then we can run-time prune during
>> startup of the executor.
>
> This does not refute my question.  Why doesn't the same logic apply
> to any stable expression?  That is, ISTM a Param is a special case
> of that.

Okay, maybe we don't need to know which external params exist, but we
need to know if there are any exec params so that we don't try to
evaluate an expression with any of those during executor startup.

I'll produce a patch which simplifies things in that area.

Thanks for looking at this.

-- 
 David Rowley                   http://www.2ndQuadrant.com/
 PostgreSQL Development, 24x7 Support, Training & Services

Commits

  1. Fix up run-time partition pruning's use of relcache's partition data.

  2. Fix access to just-closed relcache entry.

  3. Improve ExecFindInitialMatchingSubPlans's subplan renumbering logic.

  4. Improve commentary about run-time partition pruning data structures.

  5. Fix run-time partition pruning code to handle NULL values properly.

  6. Assorted cosmetic cleanup of run-time-partition-pruning code.

  7. Relocate partition pruning structs to a saner place.

  8. Improve run-time partition pruning to handle any stable expression.

  9. Support partition pruning at execution time