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> From: Justin Pryzby <pryzby@telsasoft.com> > Sent: Saturday, December 7, 2019 2:25 AM > To: Lars Aksel Opsahl <Lars.Opsahl@nibio.no> > Cc: pgsql-performance@lists.postgresql.org <pgsql-performance@lists.postgresql.org> > Subject: Re: How to run in parallel in Postgres > > On Thu, Dec 05, 2019 at 12:10:42PM +0000, Lars Aksel Opsahl wrote: > > I have a function that prepares data, so the big job can be run it in parallel. > > > > 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 ? > > SELECT find_overlap_gap_single_cell('test_data.overlap_gap_input_t1','geom',4258,'test_data.overlap_gap_input_t1_res',1,28); > SELECT find_overlap_gap_single_cell('test_data.overlap_gap_input_t1','geom',4258,'test_data.overlap_gap_input_t1_res',2,28); > SELECT find_overlap_gap_single_cell('test_data.overlap_gap_input_t1','geom',4258,'test_data.overlap_gap_input_t1_res',3,28); > ... > > I see that find_overlap_gap_single_cell creates tables, so cannot be run in parallel. > Maybe you could consider rewriting it to return data to its caller instead. > You'd also need to mark it as PARALLEL SAFE, of course. > Your other functions involved should be PARALLEL SAFE too. > > Justin Hi Justin
The reason why I don't return the results Is that on very bug tables I usually get memory problems if I return all the results to the master function. So I usually break thing up into small unlogged tables. Then I work on each table
separately or in groups. When all steps are done i merge all the small tables together. I this case we only single step, but usually I work many more steps.
But I will keep mind that it may work i parallel if I don't create any child tables but returns the result.
Thanks.
Lars
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