Re: Shmem queue is not flushed if receiver is not yet attached

On Tue, 24 May 2022 at 23:05, Robert Haas <robertmhaas(at)gmail(dot)com> wrote:
> On Thu, Mar 17, 2022 at 3:13 AM Pavan Deolasee <pavan(dot)deolasee(at)gmail(dot)com> wrote:
>> While testing on the current PG master, I noticed a problem between backends communicating over a shared memory queue. I think `shm_mq_sendv()` fails to flush the queue, even if `force_flush` is set to true, if the receiver is not yet attached to the queue. This simple fix solves the problem for me.
>>
>> On another note, `shm_mq.h` declares `shm_mq_flush()`, but I don't see it being implemented. Maybe just a leftover from the previous work? Though it seems useful to implement that API.
>
> I think that this patch is basically correct, except that it's not
> correct to set mqh_counterparty_attached when receiver is still NULL.
> Here's a v2 where I've attempted to correct that while preserving the
> essence of your proposed fix.
>
> I'm not sure that we need a shm_mq_flush(), but we definitely don't
> have one currently, so I've also adjusted your patch to remove the
> dead prototype.
>
> Please let me know your thoughts on the attached.
>
> Thanks,

Hi,

I have a problem that is also related to shmem queue [1], however, I cannot
reproduce it. How did you reproduce this problem?

[1] https://www.postgresql.org/message-id/MEYP282MB1669C8D88F0997354C2313C1B6CA9%40MEYP282MB1669.AUSP282.PROD.OUTLOOK.COM

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