From: Tom Lane <tgl@sss.pgh.pa.us>
To: Teja Jakkidi <teja.jakkidi05@gmail.com>
Cc: pgsql-admin <pgsql-admin@lists.postgresql.org>
Subject: Re: Workers in Postgres
Date: Mon, 25 Jul 2022 22:44:48 -0400
Message-ID: <2122536.1658803488@sss.pgh.pa.us> (raw)
In-Reply-To: <BBAD8621-02B5-4978-BC53-EC8759A7B55B@gmail.com>
References: <BBAD8621-02B5-4978-BC53-EC8759A7B55B@gmail.com>
Teja Jakkidi <teja.jakkidi05@gmail.com> writes:
> 1. What is a worker process exactly in Postgres?
It's a background process that can be started if the planner decides
that a particular query would benefit from parallelization. If so,
the original session process (the "leader") cooperates with one or
more temporarily-spawned workers to perform the query.
> 2. is max_parallel_workers specific to a session or instance. My max_parallel_workers is set to 8. If it is specific to instance, does it mean at any point of time I can only see 8 parallel processes despite the number of transactions in the db?
Per instance. There is a different knob max_parallel_workers_per_gather
that gives you some control over how many workers a given leader will
try to use.
Before you say "oh, I've got max_connections set to 100, so I'd better
raise max_parallel_workers to a few hundred" ... don't do that unless
you've got a few hundred CPUs in the machine. While session processes
might be sitting around doing nothing much except waiting for the next
query, workers generally are busy throughout their lifespan. So it's
counterproductive for max_parallel_workers to be more than roughly the
number of available CPUs --- setting it higher just encourages the
system to create parallel workers that it can't use effectively.
> 3. Does number of worker process have anything to do with active connections to the database.
See above.
regards, tom lane
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To: pgsql-admin@postgresql.org
Cc: tgl@sss.pgh.pa.us, teja.jakkidi05@gmail.com, pgsql-admin@lists.postgresql.org
Subject: Re: Workers in Postgres
In-Reply-To: <2122536.1658803488@sss.pgh.pa.us>
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