From: | Philip Semanchuk <philip(at)americanefficient(dot)com> |
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To: | Thorsten Schöning <tschoening(at)am-soft(dot)de> |
Cc: | pgsql-general(at)lists(dot)postgresql(dot)org |
Subject: | Re: How does Postgres decide if to use additional workers? |
Date: | 2021-02-10 14:22:58 |
Message-ID: | C8DDB51D-A655-4B20-B3CA-82B2EA759F96@americanefficient.com |
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Thread: | |
Lists: | pgsql-general |
> On Feb 9, 2021, at 10:52 AM, Thorsten Schöning <tschoening(at)am-soft(dot)de> wrote:
>
> So, based on which facts does Postgres decide if to use aadditional
> workers or not? Can I see those decisions explained somewhere? I don't
> see anything in the query plan. Thanks!
Hi Thorsten,
This is an interesting topic for me too. here’s a formula for the max number of workers that Postgres will consider for a table. Of course, most queries use more than just one table, and I don’t yet understand how Postgres handles the situation where the formula suggests multiple workers for some tables and a single worker for others.
There was some conversation about this on the performance mailing list in June. Here’s a link to the message that contains the formula; there’s more items of interest in the whole thread:
https://www.postgresql.org/message-id/89423FD3-0F13-447D-8D9E-EB1722150F94%40americanefficient.com
Hope this helps
Philip
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