| From: | tushar <tushar(dot)ahuja(at)enterprisedb(dot)com> |
|---|---|
| To: | Julien Rouhaud <julien(dot)rouhaud(at)dalibo(dot)com>, Robert Haas <robertmhaas(at)gmail(dot)com>, Amit Kapila <amit(dot)kapila16(at)gmail(dot)com> |
| Cc: | James Sewell <james(dot)sewell(at)lisasoft(dot)com>, David Rowley <david(dot)rowley(at)2ndquadrant(dot)com>, PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org>, Paul Ramsey <pramsey(at)cleverelephant(dot)ca>, Andreas Ulbrich <andreas(dot)ulbrich(at)matheversum(dot)de> |
| Subject: | Re: Choosing parallel_degree |
| Date: | 2016-04-12 12:52:13 |
| Message-ID: | 570CEF7D.3000209@enterprisedb.com |
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| Lists: | pgsql-hackers |
On 04/11/2016 08:57 PM, Julien Rouhaud wrote:
>> >Expected = Expecting worker8 information , also loops=10 (including the
>> >Master)
>> >
> Even if you set a per-table parallel_degree higher than
> max_parallel_degree, it'll be maxed at max_parallel_degree.
>
> Then, the explain shows that the planner assumed it'll launch 9 workers,
> but only 8 were available (or needed perhaps) at runtime.
>
Right, if we increase max_worker_processes value in postgresql.conf file
then
we are able to see the worker information in explain plan.
if parallel_degree value is higher than max_parallel_degree i.e
parallel_degree = 20, max_parallel_degree=10 => [ select query
accepting 10 workers ]
but in general where table doesn't have parallel_degree set and
max_parallel_degree is
set to 10 then select query is showing only 2 workers .
--
regards,tushar
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