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This new field tracks the PID of the group leader used with parallel query. For parallel workers and the leader, the value is set to the PID of the group leader. So, for the group leader, the value is the same as its own PID. Note that this reflects what PGPROC stores in shared memory, so as leader_pid is NULL if a backend has never been involved in parallel query. If the backend is using parallel query or has used it at least once, the value is set until the backend exits. Author: Julien Rouhaud Reviewed-by: Sergei Kornilov, Guillaume Lelarge, Michael Paquier, Tomas Vondra Discussion: https://postgr.es/m/CAOBaU_Yy5bt0vTPZ2_LUM6cUcGeqmYNoJ8-Rgto+c2+w3defYA@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/.