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This is required as it is no safer for two related processes to extend the same relation at a time than for unrelated processes to do the same. We don't acquire a heavyweight lock on any other object after relation extension lock which means such a lock can never participate in the deadlock cycle. So, avoid checking wait edges from this lock. This provides an infrastructure to allow parallel operations like insert, copy, etc. which were earlier not possible as parallel group members won't conflict for relation extension lock. Author: Dilip Kumar, Amit Kapila Reviewed-by: Amit Kapila, Kuntal Ghosh and Sawada Masahiko Discussion: https://postgr.es/m/CAD21AoCmT3cFQUN4aVvzy5chw7DuzXrJCbrjTU05B+Ss=Gn1LA@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/.