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If the toplevel scan/join target list is parallel-safe, postpone generating Gather (or Gather Merge) paths until after the toplevel has been adjusted to return it. This (correctly) makes queries with expensive functions in the target list more likely to choose a parallel plan, since the cost of the plan now reflects the fact that the evaluation will happen in the workers rather than the leader. The original complaint about this problem was from Jeff Janes. If the toplevel scan/join relation is partitioned, recursively apply the changes to all partitions. This sometimes allows us to get rid of Result nodes, because Append is not projection-capable but its children may be. It also cleans up what appears to be incorrect SRF handling from commit e2f1eb0ee30d144628ab523432320f174a2c8966: the old code had no knowledge of SRFs for child scan/join rels. Because we now use create_projection_path() in some cases where we formerly used apply_projection_to_path(), this changes the ordering of columns in some queries generated by postgres_fdw. Update regression outputs accordingly. Patch by me, reviewed by Amit Kapila and by Ashutosh Bapat. Other fixes for this problem (substantially different from this version) were reviewed by Dilip Kumar, Amit Khandekar, and Marina Polyakova. Discussion: http://postgr.es/m/CAMkU=1ycXNipvhWuweUVpKuyu6SpNjF=yHWu4c4US5JgVGxtZQ@mail.gmail.com
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: https://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 https://www.postgresql.org/download/. For more information look at our web site located at https://www.postgresql.org/.