Horton

Re: LISTEN/NOTIFY testing woes

Mark Dilger <hornschnorter@gmail.com>

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From: Mark Dilger <hornschnorter@gmail.com>
To: Tom Lane <tgl@sss.pgh.pa.us>, pgsql-hackers@lists.postgresql.org
Cc: Martijn van Oosterhout <kleptog@gmail.com>
Date: 2019-11-24T04:50:52Z
Lists: pgsql-hackers 

On 11/23/19 5:01 PM, Tom Lane wrote:
> I ran into a couple of issues while trying to devise a regression test
> illustrating the LISTEN-in-serializable-transaction issue Mark Dilger
> reported.  The first one is that an isolation test in which we expect
> to see a cross-process NOTIFY immediately after a COMMIT turns out to
> be not very stable: on my machine, it works as long as you're just
> running the isolation tests by themselves, but it usually falls over
> if I'm running check-world with any amount of parallelism.  The reason
> for this seems to be that incoming notifies are only checked for when
> we're about to wait for client input.  At that point we've already
> sent the ReadyForQuery ('Z') protocol message, which will cause libpq
> to stand down from looking for more input and return a null from
> PQgetResult().  Depending on timing, the following Notify protocol
> messages might arrive quickly enough that isolationtester.c sees them
> before it goes off to do something else, but that's not very reliable.

Thanks for working on this, Tom.

I have finished reading and applying your three patches and have moved 
on to testing them.  I hope to finish the review soon.




-- 
Mark Dilger

Commits

  1. Avoid assertion failure with LISTEN in a serializable transaction.

  2. Stabilize NOTIFY behavior by transmitting notifies before ReadyForQuery.

  3. Stabilize the results of pg_notification_queue_usage().