Re: Choosing parallel_degree - Mailing list pgsql-hackers

From Simon Riggs
Subject Re: Choosing parallel_degree
Date
Msg-id CANP8+jLJMXw4amnNRmQdZC9i7r6+3xZiPmUf3iB0x4CBcfKNPA@mail.gmail.com
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In response to Re: Choosing parallel_degree  (Amit Kapila <amit.kapila16@gmail.com>)
List pgsql-hackers
On 12 April 2016 at 07:58, Amit Kapila <amit.kapila16@gmail.com> wrote:
On Tue, Apr 12, 2016 at 3:15 AM, Simon Riggs <simon@2ndquadrant.com> wrote:
On 8 April 2016 at 17:49, Robert Haas <robertmhaas@gmail.com> wrote:
 
With the patch, you can - if you wish - substitute
some other number for the one the planner comes up with.

I saw you're using AccessExclusiveLock, the reason being it affects SELECTs.

That is supposed to apply when things might change the answer from a SELECT, whereas this affects only the default for a plan.


By this theory, shouldn't any other parameter like n_distinct_inherited which just effects the plan required lower lock level?

It should, yes, and I'm as surprised to see it isn't as you are.

Thread: Fabrizio was asked by Robert to provide or document an analysis of why each setting was OK to change; 9 days later he had not done so or replied, so I committed a reduced version of the patch that matched existing tests and code comments.

I guess we could have salvaged some more from it, but we didn't and there's never enough time. 

If RMT allows, that can be changed or it can wait.

--
Simon Riggs                http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services

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