Обсуждение: Re: ERROR: too many dynamic shared memory segments

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

On Fri, Feb 2, 2018 at 3:01 PM, Tom Lane <tgl@sss.pgh.pa.us> wrote:
> 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?

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

Robert Haas <robertmhaas@gmail.com> writes:
> On Fri, Feb 2, 2018 at 3:01 PM, Tom Lane <tgl@sss.pgh.pa.us> wrote:
>> 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)).

OK, that'd work too.  I'll make it so.

            regards, tom lane