Re: parallel mode and parallel contexts

On Tue, Jan 13, 2015 at 1:33 AM, Robert Haas <robertmhaas(at)gmail(dot)com> wrote:
>
> On Thu, Jan 8, 2015 at 6:52 AM, Amit Kapila <amit(dot)kapila16(at)gmail(dot)com>
wrote:
> > + seg = dsm_attach(DatumGetInt32(main_arg));
> >
> > Here, I think DatumGetUInt32() needs to be used instead of
> > DatumGetInt32() as the segment handle is uint32.
>
> OK, I'll change that in the next version.
>

No issues, I have another question related to below code:

+HandleParallelMessages(void)
+{
..
..
+ for (i = 0; i < pcxt->nworkers; ++i)
+ {
+ /*
+ * Read messages for as long as we have an error queue; if we
+ * have hit (or hit while reading) ReadyForQuery, this will go to
+ * NULL.
+ */
+ while (pcxt->worker[i].error_mqh != NULL)
+ {
+ shm_mq_result res;
+
+ CHECK_FOR_INTERRUPTS();
+
+ res = shm_mq_receive(pcxt->worker[i].error_mqh, &nbytes,
+ &data, true);
+ if (res == SHM_MQ_SUCCESS)

Here we are checking the error queue for all the workers and this loop
will continue untill all have sent ReadyForQuery() message ('Z') which
will make this loop continue till all workers have finished their work.
Assume situation where first worker has completed the work and sent
'Z' message and second worker is still sending some tuples, now above
code will keep on waiting for 'Z' message from second worker and won't
allow to receive tuples sent by second worker till it send 'Z' message.

As each worker send its own 'Z' message after completion, so ideally
the above code should receive the message only for worker which has
sent the message. I think for that it needs worker information who has
sent the message.

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