Re: ERROR: too many dynamic shared memory segments

On Fri, Feb 2, 2018 at 3:01 PM, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
> Robert Haas <robertmhaas(at)gmail(dot)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?

Hrm, I guess I could have done something like
shm_toc_lookup(pcxt->toc, PARALLEL_KEY_ERROR_QUEUE, (pcxt->nworkers ==
0)).

I don't mind much if you change it, but I will note that for the
record, before d46633506, we had a theoretical source of bugs, whereas
after that commit, we had a bug. 445dbd82a fixed that; if you change
this around again, please take care not to make it buggy again.
Otherwise, I'll be the one who is quite distressed. :-)

--
Robert Haas
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company