Horton

Re: Instability in select_parallel regression test

Robert Haas <robertmhaas@gmail.com>

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From: Robert Haas <robertmhaas@gmail.com>
To: Amit Kapila <amit.kapila16@gmail.com>
Cc: Tom Lane <tgl@sss.pgh.pa.us>, pgsql-hackers <pgsql-hackers@postgresql.org>
Date: 2017-02-19T15:02:13Z
Lists: pgsql-hackers 
On Sun, Feb 19, 2017 at 6:50 PM, Amit Kapila <amit.kapila16@gmail.com> wrote:
> To close the remaining gap, don't you think we can check slot->in_use
> flag when generation number for handle and slot are same.

That doesn't completely fix it either, because
ForgetBackgroundWorker() also does
BackgroundWorkerData->parallel_terminate_count++, which we might also
fail to see, which would cause RegisterDynamicBackgroundWorker() to
bail out early.  There are CPU ordering effects to think about here,
not just the order in which the operations are actually performed.

-- 
Robert Haas
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company

Commits

  1. Notify bgworker registrant after freeing worker slot.

  2. Replace min_parallel_relation_size with two new GUCs.

  3. Allow parallel workers to execute subplans.