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As noted by Noah Misch, btree_xlog_delete_get_latestRemovedXid is critically dependent on the assumption that it's examining a consistent state of the database. This was undocumented though, so the seemingly-unrelated check for no active HS sessions might be thought to be merely an optional optimization. Improve comments, and add an explicit check of reachedConsistency just to be sure. This function returns InvalidTransactionId (thereby killing all HS transactions) in several cases that are not nearly unlikely enough for my taste. This commit doesn't attempt to fix those deficiencies, just document them. Back-patch to 9.2, not from any real functional need but just to keep the branches more closely synced to simplify possible future back-patching.
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/.