Horton

Re: executor relation handling

Robert Haas <robertmhaas@gmail.com>

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From: Robert Haas <robertmhaas@gmail.com>
To: Tom Lane <tgl@sss.pgh.pa.us>
Cc: Amit Langote <Langote_Amit_f8@lab.ntt.co.jp>, David Rowley <david.rowley@2ndquadrant.com>, Alvaro Herrera <alvherre@2ndquadrant.com>, Jesper Pedersen <jesper.pedersen@redhat.com>, Amit Langote <amitlangote09@gmail.com>, "pgsql-hackers@postgresql.org" <pgsql-hackers@postgresql.org>
Date: 2018-10-09T18:27:44Z
Lists: pgsql-hackers 
On Sat, Oct 6, 2018 at 2:59 PM Tom Lane <tgl@sss.pgh.pa.us> wrote:
> The reasons why we need locks on tables not physically accessed by the
> query are (a) to ensure that we've blocked, or received sinval messages
> for, any DDL related to views or partition parent tables, in case that
> would invalidate the plan; (b) to allow firing triggers safely, in
> the case of partition parent tables.  Neither of these issues apply to
> a parallel worker -- the plan is already frozen before it can ever
> start, and it isn't going to be firing any triggers either.

That last part could *easily* change in a future release.  We've
already started to allow CTAS with parallel query, and there have
already been multiple people wanting to allow more.  It would be a
shame if we threw up additional obstacles in the way of that...

-- 
Robert Haas
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company

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.