On Thu, Jun 15, 2017 at 7:42 PM, Robert Haas <robertmh...@gmail.com> wrote:
> On Thu, Jun 15, 2017 at 10:05 AM, Tom Lane <t...@sss.pgh.pa.us> wrote:
>>> Well, as Amit points out, there are entirely legitimate ways for that
>>> to happen.  If the leader finishes the whole query itself before the
>>> worker reaches the dsm_attach() call, it will call dsm_detach(),
>>> destroying the segment, and the worker will hit this ERROR.  That
>>> shouldn't happen very often in the real world, because we ought not to
>>> select a parallel plan in the first place unless the query is going to
>>> take a while to run, but the select_parallel test quite deliberately
>>> disarms all of the guards that would tend to discourage such plans.
>> But we know, from the subsequent failed assertion, that the leader was
>> still trying to launch parallel workers.  So that particular theory
>> doesn't hold water.
> Is there any chance that it's already trying to launch parallel
> workers for the *next* query?

Yes, I think it is for next query.  If you refer the log below from lorikeet:

2017-06-13 16:44:57.179 EDT [59404ec6.2758:63] LOG:  statement:
EXPLAIN (analyze, timing off, summary off, costs off) SELECT * FROM
2017-06-13 16:44:57.247 EDT [59404ec9.2e78:1] ERROR:  could not map
dynamic shared memory segment
2017-06-13 16:44:57.248 EDT [59404dec.2d9c:5] LOG:  worker process:
parallel worker for PID 10072 (PID 11896) exited with exit code 1
2017-06-13 16:44:57.273 EDT [59404ec6.2758:64] LOG:  statement: select
stringu1::int2 from tenk1 where unique1 = 1;
TRAP: FailedAssertion("!(BackgroundWorkerData->parallel_register_count
- BackgroundWorkerData->parallel_terminate_count <= 1024)", File:
Line: 974)
2017-06-13 16:45:02.652 EDT [59404dec.2d9c:6] LOG:  server process
(PID 10072) was terminated by signal 6: Aborted
2017-06-13 16:45:02.652 EDT [59404dec.2d9c:7] DETAIL:  Failed process
was running: select stringu1::int2 from tenk1 where unique1 = 1;
2017-06-13 16:45:02.652 EDT [59404dec.2d9c:8] LOG:  terminating any
other active server processes

Error "could not map dynamic shared memory segment" is due to query
"EXPLAIN .. SELECT * FROM tenk1" and Assertion failure is due to
another statement "select stringu1::int2 from tenk1 where unique1 =

With Regards,
Amit Kapila.
EnterpriseDB: http://www.enterprisedb.com

Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org)
To make changes to your subscription:

Reply via email to