Horton

Re: ERROR: too many dynamic shared memory segments

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

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From: Tom Lane <tgl@sss.pgh.pa.us>
To: Robert Haas <robertmhaas@gmail.com>
Cc: Dilip Kumar <dilipbalaut@gmail.com>, Thomas Munro <thomas.munro@enterprisedb.com>, Jakub Glapa <jakub.glapa@gmail.com>, pgsql-hackers <pgsql-hackers@postgresql.org>
Date: 2018-02-02T20:01:15Z
Lists: pgsql-hackers, pgsql-general 
Robert Haas <robertmhaas@gmail.com> writes:
> That turned out to produce more than one problem.  I find that the
> select_parallel test then fails like this:
> ERROR:  could not find key 18446744073709486082 in shm TOC at 0x10be98040
> The fix for that problem seems to be:

>      /* Recreate error queues. */
>      error_queue_space =
> -        shm_toc_lookup(pcxt->toc, PARALLEL_KEY_ERROR_QUEUE, false);
> +        shm_toc_lookup(pcxt->toc, PARALLEL_KEY_ERROR_QUEUE, true);
> +    Assert(pcxt->nworkers == 0 || error_queue_space != NULL);

I happened across this patch while preparing the release notes, and
I'm quite distressed by it, because it completely breaks the point
of what I'd done in commit d46633506 (to wit, to not just blindly
assume, nor just Assert, that shm_toc_lookup always succeeds).
Do you mind if I change that Assert to a run-time test?

			regards, tom lane

Commits

  1. Be more wary about shm_toc_lookup failure.

  2. Fix ReinitializeParallelDSM to tolerate finding no error queues.

  3. Teach bitmap heap scan to cope with absence of a DSA.

  4. Don't be so trusting that shm_toc_lookup() will always succeed.