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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
PostgreSQL Database Management System ===================================== This directory contains the source code distribution of the PostgreSQL database management system. PostgreSQL is an advanced object-relational database management system that supports an extended subset of the SQL standard, including transactions, foreign keys, subqueries, triggers, user-defined types and functions. This distribution also contains C language bindings. PostgreSQL has many language interfaces, many of which are listed here: http://www.postgresql.org/download See the file INSTALL for instructions on how to build and install PostgreSQL. That file also lists supported operating systems and hardware platforms and contains information regarding any other software packages that are required to build or run the PostgreSQL system. Copyright and license information can be found in the file COPYRIGHT. A comprehensive documentation set is included in this distribution; it can be read as described in the installation instructions. The latest version of this software may be obtained at http://www.postgresql.org/download/. For more information look at our web site located at http://www.postgresql.org/.