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: Robert Haas <robertmhaas@gmail.com>
Cc: Tom Lane <tgl@sss.pgh.pa.us>, 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: 2018-07-16T00:24:59Z
Lists: pgsql-hackers 
On 16 July 2018 at 12:12, Robert Haas <robertmhaas@gmail.com> wrote:
> On Sun, Jul 15, 2018 at 1:02 PM, Tom Lane <tgl@sss.pgh.pa.us> wrote:
>> What we'd be better off doing, if we go this route, is to install an
>> assertion-build-only test that verifies during relation_open(NoLock)
>> that some kind of lock is already held on the rel.  That would protect
>> not only the executor, but a boatload of existing places that open
>> rels with NoLock on the currently-unverified assumption that a lock is
>> already held.
>
> +1.  In fact, maybe we ought to go a little further and have a
> relation_reopen(oid, mode) that verifies that a lock in the specified
> mode is held.

Wouldn't it be better to just store the Relation indexed by its relid
somewhere the first time we opened it? Then just do a direct array
lookup on that rather than looking up by hashtable in syscache?

-- 
 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