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The SSI patch inserted a call of RegisterPredicateLockingXid into GetNewTransactionId, which was a bad idea on a couple of grounds. First, it's not necessary to hold XidGenLock while manipulating that shared memory, and doing so is bad because XidGenLock is a high-contention lock that should be held for as short a time as possible. (Not to mention that it adds an entirely unnecessary deadlock hazard, since we must take SerializableXactHashLock as well.) Second, the specific place where it was put was between extending CLOG and advancing nextXid, which could result in unpleasant behavior in case of a failure there. Pull the call out to AssignTransactionId, which is much safer and arguably better from a modularity standpoint too. There is more work to do to clean up the failure-before-advancing-nextXid issue, but that is a separate change that will need to be back-patched. So for the moment I just want to make GetNewTransactionId look the same as it did in prior versions.
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/.