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Since 9.0, removing lots of large objects in a single transaction risks exceeding max_locks_per_transaction, because we merged large object removal into the generic object-drop mechanism, which takes out an exclusive lock on each object to be dropped. This creates a hazard for contrib/vacuumlo, which has historically tried to drop all unreferenced large objects in one transaction. There doesn't seem to be any correctness requirement to do it that way, though; we only need to drop enough large objects per transaction to amortize the commit costs. To prevent a regression from pre-9.0 releases wherein vacuumlo worked just fine, back-patch commitsb69f2e3640and64c604898e, which break vacuumlo's deletions into multiple transactions with a user-controllable upper limit on the number of objects dropped per transaction. Tim Lewis, Robert Haas, Tom Lane
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/.