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We have an implementation restriction that PREPARE TRANSACTION can't handle cases where both session-lifespan and transaction-lifespan locks are held on the same lockable object. (That's because we'd otherwise need to acquire a new PROCLOCK entry during post-prepare cleanup, which is an operation that might fail. The situation can only arise with odd usages of advisory locks, so removing the restriction is probably not worth the amount of effort it would take.) AtPrepare_Locks attempted to enforce this, but its logic was many bricks shy of a load, because it only detected cases where the session and transaction locks had the same lockmode. Locks of different modes on the same object would lead to the rather unhelpful message "PANIC: we seem to have dropped a bit somewhere". To fix, build a transient hashtable with one entry per locktag, not one per locktag + mode, and use that to detect conflicts. Per bug #17122 from Alexander Pyhalov. This bug is ancient, so back-patch to all supported branches. Discussion: https://postgr.es/m/17122-04f3c32098a62233@postgresql.org
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/.