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Previously, this function acquired locks in the order using find_all_inheritors(), which locks the children of each table that it processes in ascending OID order, and which processes the inheritance hierarchy as a whole in a breadth-first fashion. Now, it processes the inheritance hierarchy in a depth-first fashion, and at each level it proceeds in the order in which tables appear in the PartitionDesc. If table inheritance rather than table partitioning is used, the old order is preserved. This change moves the locking of any given partition much closer to the code that actually expands that partition. This seems essential if we ever want to allow concurrent DDL to add or remove partitions, because if the set of partitions can change, we must use the same data to decide which partitions to lock as we do to decide which partitions to expand; otherwise, we might expand a partition that we haven't locked. It should hopefully also facilitate efforts to postpone inheritance expansion or locking for performance reasons, because there's really no way to postpone locking some partitions if we're blindly locking them all using find_all_inheritors(). The only downside of this change which is known to me is that it further deviates from the principle that we should always lock the inheritance hierarchy in find_all_inheritors() order to avoid deadlock risk. However, we've already crossed that bridge in commit 9eefba181f7782d27d85d7e94e6028371e7ab2d7 and there are futher patches pending that make similar changes, so this isn't really giving up anything that we haven't surrendered already -- and it seems entirely worth it, given the performance benefits some of those changes seem likely to bring. Patch by me; thanks to David Rowley for discussion of these issues. Discussion: http://postgr.es/m/CAKJS1f_eEYVEq5tM8sm1k-HOwG0AyCPwX54XG9x4w0zy_N4Q_Q@mail.gmail.com Discussion: http://postgr.es/m/CA+TgmoZUwPf_uanjF==gTGBMJrn8uCq52XYvAEorNkLrUdoawg@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/.