[postgis-tickets] [PostGIS] #3752: Mark all aggregates raster and geometry as parallel safe

[PostGIS]

#3752: Mark all aggregates raster and geometry as parallel safe
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 Reporter:  robe     |      Owner:  pramsey
     Type:  defect   |     Status:  new
 Priority:  high     |  Milestone:  PostGIS 2.4.0
Component:  postgis  |    Version:  trunk
 Keywords:           |
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 Mark all PostGIS aggregates as safe.

 As kompaz pointed out in #3751, there isn't any harm in doing this.

 However since this isn't really a bug, I'm not going to backport the
 change to 2.3.  Just going to do for 2.4.  I still think in most cases the
 work can't be done in a parallel worker since the same groupings are not
 guaranteed to happen in the same worker and since there is no combine
 function, it can't regroup the worker groups.

 That's one reason why it's not worth the bother pushing to 2.3. Since
 create aggregate still requires a drop and recreate, might cause more
 damage than good since some folks may not be able to cleanly upgrade 2.3
 minor.

 With PostgreSQL 10 there are also many more strategies supported for
 parallelism, so definitely more worth while.

 From release notes of 10


 {{{

 Support parallel btree index scans (Rahila Syed, Amit Kapila, Robert Haas,
 Rafia Sabih)

 Allows btree index pages to be checked by separate parallel workers.

 Support parallel bitmap heap scans (Dilip Kumar)

 This allows a single index scan to dispatch parallel workers to process
 different areas of the heap.

 Allow merge joins to be performed in parallel (Dilip Kumar)

 Allow non-correlated subqueries to be run in parallel (Amit Kapila)

 Improve ability of parallel workers to return pre-sorted data (Rushabh
 Lathia)

 }}}

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Ticket URL: <https://trac.osgeo.org/postgis/ticket/3752>
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