Horton

Re: why partition pruning doesn't work?

Ashutosh Bapat <ashutosh.bapat@enterprisedb.com>

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From: Ashutosh Bapat <ashutosh.bapat@enterprisedb.com>
To: Jeff Janes <jeff.janes@gmail.com>
Cc: Tom Lane <tgl@sss.pgh.pa.us>, Dmitry Dolgov <9erthalion6@gmail.com>, Pavel Stehule <pavel.stehule@gmail.com>, PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>
Date: 2018-06-02T21:52:05Z
Lists: pgsql-hackers 
On Sat, Jun 2, 2018 at 5:16 PM, Jeff Janes <jeff.janes@gmail.com> wrote:
> On Fri, Jun 1, 2018 at 11:53 AM, Tom Lane <tgl@sss.pgh.pa.us> wrote:
>>
>>
>> I agree though that it seems strange to special-case SQLValueFunction
>> rather than any-stable-expression.  As long as the evaluation happens
>> at executor start (i.e. with the query's run-time snapshot) it should
>> be reasonable to simplify any stable expression.
>>
>> It's worth questioning whether this is a bug fix or an improvement.
>> If the latter, it probably ought to wait for v12.
>
>
> If explaining the change requires reference to tokens from the source code,
> rather than something an end user could understand, I'd argue it is a bug
> fix rather than an improvement.

If we going to implement stable expression folding before the actual
execution starts, that's a feature in itself. So, it's V12 material.
Partition pruning will use that feature. I don't think we should make
partition pruning work with stable expressions in some ad-hoc way in
V11 and the some future release (mostly V12) implements it on top of
stable expression folding feature. So my vote for making it work in
V12.

-- 
Best Wishes,
Ashutosh Bapat
EnterpriseDB Corporation
The Postgres Database Company

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