[postgis-tickets] [PostGIS] #3751: Parallel support for aggregates with transitions

[PostGIS]

#3751: Parallel support for aggregates with transitions
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  Reporter:  robe         |      Owner:  pramsey
      Type:  enhancement  |     Status:  new
  Priority:  high         |  Milestone:  PostGIS 2.4.0
 Component:  postgis      |    Version:  2.3.x
Resolution:               |   Keywords:
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Changes (by robe):

 * cc: pramsey (added)


Comment:

 I was hoping this was an already tested bit, but it seems I was mistaken,
 array_agg and string_agg do not use the new serialfunc, deserialfunc.
 Most cases I found in postgresql source code are a bit trivial-er.  I
 asked on mailing list why this is so, and seems they might not have gotten
 to it.

 Last comment from  Andres Freund:

 https://www.postgresql.org/message-
 id/20170606192609.lgwzs2pcr4ng7et5%40alap3.anarazel.de


 {{{
 > > It seems CREATE  AGGREGATE was expanded in 9.6 to support
 parallelization of
 > > aggregate functions using transitions, with the addition of serialfunc
 and
 > > deserialfunc to the aggregate definitions.
 > >
 > > https://www.postgresql.org/docs/10/static/sql-createaggregate.html
 > >
 > > I was looking at the PostgreSQL 10 source code for some example usages
 of
 > > this and was hoping that array_agg and string_agg would support the
 feature.
 > > At a cursory glance, it seems they do not use this.
 > > Examples I see that do support it are the average and standard
 deviation
 > > functions.
 > >
 > > Is there a reason for this or it just wasn't gotten to?

 I'd suggest trying to write a parallel version of them ;).  Shouldn't be
 too hard.
 }}}

 @pramsey have you had a chance to look at this yet?

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Ticket URL: <https://trac.osgeo.org/postgis/ticket/3751#comment:2>
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