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Previously, a session that had created temporary objects could hang during exit if its default transaction mode was SERIALIZABLE READ ONLY DEFERRABLE and a concurrent serializable transaction was prepared. During backend exit, temporary-relation cleanup pushed a regular transaction snapshot, which honored the session's default settings and could wait for a safe serializable snapshot. So, if the conflicting transaction was prepared, this wait could last indefinitely. The wait occurred while the backend was already exiting and interrupts were held off, so even pg_terminate_backend() could not cancel it. The backend therefore remained until the prepared transaction was resolved. Temporary-relation cleanup only needs an active MVCC snapshot for fetching TOAST data from catalog tuples while dropping temporary objects. It does not need a transaction snapshot affected by the user's default isolation settings. So, use a catalog snapshot instead, which provides the needed protection without entering the deferrable safe-snapshot wait. Backpatch to all supported versions. Bug: #19441 Reported-by: Alexander Lakhin <exclusion@gmail.com> Author: Andrey Rachitskiy <pl0h0yp1@gmail.com> Reviewed-by: Andrey Borodin <x4mmm@yandex-team.ru> Reviewed-by: Fujii Masao <masao.fujii@gmail.com> Discussion: https://postgr.es/m/19441-ec29f3b1363b4a68@postgresql.org Backpatch-through: 14
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/.