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While choosing an autogenerated name for an index, look for pre-existing relations using a SnapshotDirty snapshot, instead of the previous behavior that considered only committed-good pg_class rows. This allows us to detect and avoid conflicts against indexes that are still being built. It's still possible to fail due to a race condition, but the window is now just the amount of time that it takes DefineIndex to validate all its parameters, call smgrcreate(), and enter the index's pg_class row. Formerly the race window covered the entire time needed to create and fill an index, which could be very long if the table is large. Worse, if the conflicting index creation is part of a larger transaction, it wouldn't be visible till COMMIT. So this isn't a complete solution, but it should greatly ameliorate the problem, and the patch is simple enough to be back-patchable. It might at some point be useful to do the same for pg_constraint entries (cf. ChooseConstraintName, ConstraintNameExists, and related functions). However, in the absence of field complaints, I'll leave that alone for now. The relation-name test should be good enough for index-based constraints, while foreign-key constraints seem to be okay since they require exclusive locks to create. Bug: #18959 Reported-by: Maximilian Chrzan <maximilian.chrzan@here.com> Author: Tom Lane <tgl@sss.pgh.pa.us> Reviewed-by: Dilip Kumar <dilipbalaut@gmail.com> Discussion: https://postgr.es/m/18959-f63b53b864bb1417@postgresql.org Backpatch-through: 13
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/.