Re: Shmem queue is not flushed if receiver is not yet attached - Mailing list pgsql-hackers

From Robert Haas
Subject Re: Shmem queue is not flushed if receiver is not yet attached
Date
Msg-id CA+TgmobTkgXcMsj1EXg=J006oeLcKHPsE-vS8eTRa6NjwfjVng@mail.gmail.com
Whole thread Raw
In response to Shmem queue is not flushed if receiver is not yet attached  (Pavan Deolasee <pavan.deolasee@gmail.com>)
Responses Re: Shmem queue is not flushed if receiver is not yet attached
Re: Shmem queue is not flushed if receiver is not yet attached
List pgsql-hackers
On Thu, Mar 17, 2022 at 3:13 AM Pavan Deolasee <pavan.deolasee@gmail.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
yetattached 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
fromthe 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,

--
Robert Haas
EDB: http://www.enterprisedb.com

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