Message-ID: <65371f0819be9dc954fdece32e9df30d1c5aa39e.camel@cybertec.at>
Subject: Re: How to run in parallel in Postgres
From: Laurenz Albe <laurenz.albe@cybertec.at>
To: Lars Aksel Opsahl <Lars.Opsahl@nibio.no>,
	"pgsql-performance@lists.postgresql.org"
	 <pgsql-performance@lists.postgresql.org>
Date: Thu, 05 Dec 2019 17:42:06 +0100
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On Thu, 2019-12-05 at 12:10 +0000, Lars Aksel Opsahl wrote:
> have a function that prepares data, so the big job can be run it in parallel. 
> 
> Today I have solved this by using "Gnu parallel" like this.
> psql testdb -c"\! psql -t -q -o /tmp/run_cmd.sql testdb -c\"SELECT find_overlap_gap_make_run_cmd('sl_lop.overlap_gap_input_t1','geom',4258,'sl_lop.overlap_gap_input_t1_res',50);\"; parallel -j 4 
> psql testdb -c :::: /tmp/run_cmd.sql" 2>> /tmp/analyze.log;
> 
> The problem here is that I depend on external code which may not be installed. 
> 
> Since Postgres now supports parallel I was wondering if it's easy to trigger parallel dynamically created SQL calls.
> 
> If you look at https://github.com/larsop/find-overlap-and-gap/blob/master/src/test/sql/regress/find_overlap_and_gap.sql  you see that
> find_overlap_gap_make_run_cmd generates as set of 28 sql calls. 
> 
> So is it in a simple way possible to use Postgres parallel functionality to call this 28 functions i parallel so I don't have dependent on externally install programs  ?
> 
> When this 28 sql calls are done, the find_overlap_gap_make_run_cmd may continue to the next step of work. So the function that triggers parallel calls wait for them complete and then may start on
> the next step of work.

You cannot run several queries in parallel in a PostgreSQL function.

You may want to have a look at PL/Proxy which might be used for things like that.

Yours,
Laurenz Albe
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