Horton

Re: why partition pruning doesn't work?

Amit Langote <langote_amit_f8@lab.ntt.co.jp>

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From: Amit Langote <Langote_Amit_f8@lab.ntt.co.jp>
To: Tom Lane <tgl@sss.pgh.pa.us>, Robert Haas <robertmhaas@gmail.com>
Cc: David Rowley <david.rowley@2ndquadrant.com>, 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: 2018-06-14T07:17:26Z
Lists: pgsql-hackers

Attachments

On 2018/06/13 23:39, Tom Lane wrote:
> Robert Haas <robertmhaas@gmail.com> writes:
>> Seems reasonable.  Really, I think we should look for a way to hang
>> onto the relation at the point where it's originally opened and locked
>> instead of reopening it here.  But that's probably more invasive than
>> we can really justify right at the moment, and I think this is a step
>> in a good direction.
> 
> The existing coding there makes me itch a bit, because there's only a
> rather fragile line of reasoning justifying the assumption that there is a
> pre-existing lock at all.  So I'd be in favor of what you suggest just to
> get rid of the "open(NoLock)" hazard.  But I agree that it'd be rather
> invasive and right now is probably not the time for it.

I had sent a patch to try to get rid of the open(NoLock) there a couple of
months ago [1].  The idea was to both lock and open the relation in
ExecNonLeafAppendTables, which is the first time all partitioned tables in
a given Append node are locked for execution.  Also, the patch makes it a
responsibility of ExecEndAppend to release the relcache pins, so the
recently added ExecDestroyPartitionPruneState would not be needed.

Attached is a rebased version of that patch if there is interest in it.

Thanks,
Amit

[1]
https://www.postgresql.org/message-id/0b361a22-f995-e15c-a385-6d1b72dd0d13%40lab.ntt.co.jp

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