Horton

Re: ERROR: too many dynamic shared memory segments

Dilip Kumar <dilipbalaut@gmail.com>

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From: Dilip Kumar <dilipbalaut@gmail.com>
To: Thomas Munro <thomas.munro@enterprisedb.com>
Cc: Jakub Glapa <jakub.glapa@gmail.com>, Forums postgresql <pgsql-general@postgresql.org>, Robert Haas <robertmhaas@gmail.com>, pgsql-hackers <pgsql-hackers@postgresql.org>
Date: 2017-11-28T07:32:56Z
Lists: pgsql-hackers, pgsql-general

Attachments

On Tue, Nov 28, 2017 at 4:18 AM, Thomas Munro <thomas.munro@enterprisedb.com
> wrote:

> On Tue, Nov 28, 2017 at 10:05 AM, Jakub Glapa <jakub.glapa@gmail.com>
> wrote:
> > As for the crash. I dug up the initial log and it looks like a
> segmentation
> > fault...
> >
> > 2017-11-23 07:26:53 CET:192.168.10.83(35238):user@db:[30003]: ERROR:
> too
> > many dynamic shared memory segments
>
> I think there are two failure modes: one of your sessions showed the
> "too many ..." error (that's good, ran out of slots and said so and
> our error machinery worked as it should), and another crashed with a
> segfault, because it tried to use a NULL "area" pointer (bad).  I
> think this is a degenerate case where we completely failed to launch
> parallel query, but we ran the parallel query plan anyway and this
> code thinks that the DSA is available.  Oops.
>

 I think BitmapHeapScan check whether dsa is valid or not if DSA is not
valid then it should assume it's non-parallel plan.

Attached patch should fix the issue.

-- 
Regards,
Dilip Kumar
EnterpriseDB: http://www.enterprisedb.com

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.