Fix testing of parallel-safety of SubPlans. is_parallel_safe() supposed that the only relevant property of a SubPlan was the parallel safety of the referenced subplan tree. This is wrong: the testexpr or args subtrees might contain parallel-unsafe stuff, as demonstrated by the test case added here. However, just recursing into the subtrees fails in a different way: we'll typically find PARAM_EXEC Params representing the subplan's output columns in the testexpr. The previous coding supposed that any Param must be treated as parallel-restricted, so that a naive attempt at fixing this disabled parallel pushdown of SubPlans altogether. We must instead determine, for any visited Param, whether it is one that would be computed by a surrounding SubPlan node; if so, it's safe to push down along with the SubPlan node.
We might later be able to extend this logic to cope with Params used for correlated subplans and other cases; but that's a task for v11 or beyond. Tom Lane and Amit Kapila Discussion: https://postgr.es/m/7064.1492022...@sss.pgh.pa.us Branch ------ master Details ------- https://git.postgresql.org/pg/commitdiff/39151781c8cd2c8bf6057496426fb9c07178eda5 Modified Files -------------- src/backend/optimizer/util/clauses.c | 44 ++++++++++++++++++++++++--- src/include/nodes/primnodes.h | 3 +- src/test/regress/expected/select_parallel.out | 12 ++++++++ src/test/regress/sql/select_parallel.sql | 4 +++ 4 files changed, 57 insertions(+), 6 deletions(-) -- Sent via pgsql-committers mailing list (pgsql-committers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-committers
