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To lock a prepared transaction's shared memory entry, we used to mark it with the XID of the backend. When the XID was no longer active according to the proc array, the entry was implicitly considered as not locked anymore. However, when preparing a transaction, the backend's proc array entry was cleared before transfering the locks (and some other state) to the prepared transaction's dummy PGPROC entry, so there was a window where another backend could finish the transaction before it was in fact fully prepared. To fix, rewrite the locking mechanism of global transaction entries. Instead of an XID, just have simple locked-or-not flag in each entry (we store the locking backend's backend id rather than a simple boolean, but that's just for debugging purposes). The backend is responsible for explicitly unlocking the entry, and to make sure that that happens, install a callback to unlock it on abort or process exit. Backpatch to all supported versions. |
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| README.git | ||
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README
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. 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/.