Horton

Don't allow LIMIT/OFFSET clause within sub-selects to be pushed to workers.

Amit Kapila <akapila@postgresql.org>

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Commit: 75f9c4ca5a8047d7a9cfbc7d51a610933d04dc7f
Author: Amit Kapila <akapila@postgresql.org>
Date: 2018-09-14T04:06:30Z
Releases: 12.0 
Don't allow LIMIT/OFFSET clause within sub-selects to be pushed to workers.

Allowing sub-select containing LIMIT/OFFSET in workers can lead to
inconsistent results at the top-level as there is no guarantee that the
row order will be fully deterministic.  The fix is to prohibit pushing
LIMIT/OFFSET within sub-selects to workers.

Reported-by: Andrew Fletcher
Bug: 15324
Author: Amit Kapila
Reviewed-by: Dilip Kumar
Backpatch-through: 9.6
Discussion: https://postgr.es/m/153417684333.10284.11356259990921828616@wrigleys.postgresql.org

Files

PathChange+/−
src/backend/optimizer/path/allpaths.c modified +13 −0
src/backend/optimizer/plan/planner.c modified +1 −2
src/include/optimizer/planner.h modified +2 −0
src/test/regress/expected/select_parallel.out modified +19 −0
src/test/regress/sql/select_parallel.sql modified +5 −0

Discussion