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: Andres Freund <andres@anarazel.de>, 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: 2018-10-04T19:57:40Z
Lists: pgsql-hackers 
On Thu, Oct 4, 2018 at 3:28 PM Tom Lane <tgl@sss.pgh.pa.us> wrote:
> I'm possibly confused, but I thought that the design of parallel query
> involved an expectation that workers didn't need to get their own locks.

You are, indeed, confused.  A heck of a lot of effort went into making
sure that the workers COULD take their own locks, and into trying to
make sure that didn't break anything.  That effort may or may not have
been entirely successful, but I'm pretty sure that having them NOT
take locks is going to be a lot worse.

> What we've determined so far in this thread is that workers *do* get
> their own locks (or did before yesterday), but I'd been supposing that
> that was accidental not intentional.

Nope, that was intentional.

> In any case, I definitely intend that they will be getting their own
> locks again after the dust has settled.  Panic not.

/me unloads metaphorical bazooka.

-- 
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.