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We mustn't run generate_gather_paths() during add_paths_to_joinrel(), because that function can be invoked multiple times for the same target joinrel. Not only is it wasteful to build GatherPaths repeatedly, but a later add_partial_path() could delete the partial path that a previously created GatherPath depends on. Instead establish the convention that we do generate_gather_paths() for a rel only just before set_cheapest(). The code was accidentally not broken for baserels, because as of today there never is more than one partial path for a baserel. But that assumption obviously has a pretty short half-life, so move the generate_gather_paths() calls for those cases as well. Also add some generic comments explaining how and why this all works. Per fuzz testing by Andreas Seltenreich. Report: <871t5pgwdt.fsf@credativ.de>
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/.