On 04/05/2017 04:26 PM, Kuntal Ghosh wrote:
On Wed, Apr 5, 2017 at 7:45 PM, Robert Haas <robertmh...@gmail.com> wrote:
On Wed, Apr 5, 2017 at 10:09 AM, Kuntal Ghosh
<kuntalghosh.2...@gmail.com> wrote:
Did you intend to attach that patch to this email?
Actually, I'm confused how we should ensure (register_count >
terminate_count) invariant. I think there can be a system crash what
Tomas has suggested up in the thread.
Assert(parallel_register_count - parallel_terminate_count <=
max_parallel_workers);
Backend 1 > SET max_parallel_worker = 8;
Backend 1 > Execute a long running parallel query q1 with number of
parallel worker spawned is say, 4.
At this point, parallel_register_count should be equal to
parallel_terminate_count. 4 workers were started, and 4 have
terminated.
Actually, I'm referring to the case when q1 is still running. In that
case, parallel_register_count = 4 and parallel_terminate_count = 0.
Backend 2> SET max_parallel_worker = 3;
Now, parallel_register_count - parallel_terminate_count = 4 >
max_parallel_worker.
Backend 2 > Try to execute any parallel query q2 with number of
parallel worker spawned > 0.
Hence, the assert will fail here.
Actually, you probably don't even need two sessions to trigger the
assert. All you need is to tweak the max_parallel_workers and then
reload the config while the parallel query is running. Then
ForgetBackgroundWorker() will see the new value.
regards
--
Tomas Vondra http://www.2ndQuadrant.com
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services
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