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39151781c8
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/7064.1492022469@sss.pgh.pa.us |
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