Re: Wait for parallel workers to attach

On Tue, Jan 30, 2018 at 10:10 PM, Amit Kapila <amit.kapila16@gmail.com> wrote:
>> known_started_workers looks a lot like any_message_received.  Perhaps
>> any_message_received should be renamed to known_started_workers and
>> reused here.
>
> Sure, that sounds good to me.  Do you prefer a separate patch for
> renaming any_message_received to known_started_workers or is it okay
> to have it along with the main patch?

A single patch sounds OK.

>>  After all, if we know that a worker was started, there's
>> no need for WaitForParallelWorkersToFinish to again call
>> GetBackgroundWorkerPid() for it.
>
> I think in above sentence you wanted to say
> WaitForParallelWorkersToAttach, not WaitForParallelWorkersToFinish.
> Am I right?

Yes.

>> I think that you shouldn't need the 10ms delay loop; waiting forever
>> should work.  If a work fails to start, the postmaster should send
>> SIGUSR1 which should set our latch.
>>
> I am not getting what exactly you are suggesting here.  The wait loop
> is intended for the case when some workers are not started.  We want
> to wait for sometime before checking again whether workers are
> started. I wanted to avoid busy looping waiting for some worker to
> start.  I think in most cases we don't need to wait, but for some
> corner cases where postmaster didn't get chance to start a worker, we
> should avoid busy looping waiting for a worker to start.

I agree we need to avoid busy-looping.  What I'm saying is that we
don't need a timeout.  Why do you think we need a timeout?  We have
bgw_notify_pid so that we will get a signal instead of having to poll.

-- 
Robert Haas
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