Horton

Re: executor relation handling

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>, Alvaro Herrera <alvherre@2ndquadrant.com>, Jesper Pedersen <jesper.pedersen@redhat.com>, Amit Langote <amitlangote09@gmail.com>, Pg Hackers <pgsql-hackers@postgresql.org>
Date: 2018-10-08T00:29:48Z
Lists: pgsql-hackers 
On 8 October 2018 at 13:13, Tom Lane <tgl@sss.pgh.pa.us> wrote:
> The idea I had in mind was to allow hard pruning of any leaf that's
> been excluded *at plan time* based on partition constraints seen in
> its parent rel(s).  That should be safe enough as long as we take
> locks on all the non-leaf rels --- then we'd know about any change
> in the constraint situation.
>
> Rather than coping with renumbering the RTEs, it might be easiest
> to invent an "RTE_DUMMY" RTE type that a hard-pruned RTE could be
> changed to.

The problem with that is that, if we get [1] done in PG12, then the
RTE_DUMMYs would not exist, as we'd only have RTEs in the range table
for partitions that survived plan-time pruning.

It also leaves a problem to solve in the unneeded locks being taken on
partitions for PREPAREd queries using run-time pruning.

[1] https://commitfest.postgresql.org/20/1778/

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

Commits

  1. Avoid O(N^2) cost in ExecFindRowMark().

  2. Remove some unnecessary fields from Plan trees.

  3. Restore sane locking behavior during parallel query.

  4. Remove more redundant relation locking during executor startup.

  5. In the executor, use an array of pointers to access the rangetable.

  6. Centralize executor's opening/closing of Relations for rangetable entries.

  7. Change executor to just Assert that table locks were already obtained.

  8. Change rewriter/planner/executor/plancache to depend on RTE rellockmode.

  9. Add assertions that we hold some relevant lock during relation open.

  10. Create an RTE field to record the query's lock mode for each relation.