Horton

Re: executor relation handling

Tom Lane <tgl@sss.pgh.pa.us>

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From: Tom Lane <tgl@sss.pgh.pa.us>
To: Andres Freund <andres@anarazel.de>
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>, Pg Hackers <pgsql-hackers@postgresql.org>
Date: 2018-10-04T19:27:59Z
Lists: pgsql-hackers 
Andres Freund <andres@anarazel.de> writes:
> I've not really followed this thread, and just caught up to here.  It
> seems entirely unacceptable to not acquire locks on workers to me.
> Maybe I'm missing something, but why do/did the patches in this thread
> require that / introduce that? We didn't have that kind of concept
> before, no?  The group locking stuff should rely / require that kind of
> thing, no?

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.
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.

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

			regards, tom lane

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.