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The code in PostPrepare_Locks supposed that it could reassign locks to the prepared transaction's dummy PGPROC by deleting the PROCLOCK table entries and immediately creating new ones. This was safe when that code was written, but since we invented partitioning of the shared lock table, it's not safe --- another process could steal away the PROCLOCK entry in the short interval when it's on the freelist. Then, if we were otherwise out of shared memory, PostPrepare_Locks would have to PANIC, since it's too late to back out of the PREPARE at that point. Fix by inventing a dynahash.c function to atomically update a hashtable entry's key. (This might possibly have other uses in future.) This is an ancient bug that in principle we ought to back-patch, but the odds of someone hitting it in the field seem really tiny, because (a) the risk window is small, and (b) nobody runs servers with maxed-out lock tables for long, because they'll be getting non-PANIC out-of-memory errors anyway. So fixing it in HEAD seems sufficient, at least until the new code has gotten some testing.
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: http://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. Changes between all PostgreSQL releases are recorded in the file HISTORY. 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 http://www.postgresql.org/download/. For more information look at our web site located at http://www.postgresql.org/.