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VACUUM was willing to remove a committed-dead tuple immediately if it was deleted by the same transaction that inserted it. The idea is that such a tuple could never have been visible to any other transaction, so we don't need to keep it around to satisfy MVCC snapshots. However, there was already an exception for tuples that are part of an update chain, and this exception created a problem: we might remove TOAST tuples (which are never part of an update chain) while their parent tuple stayed around (if it was part of an update chain). This didn't pose a problem for most things, since the parent tuple is indeed dead: no snapshot will ever consider it visible. But MVCC-safe CLUSTER had a problem, since it will try to copy RECENTLY_DEAD tuples to the new table. It then has to copy their TOAST data too, and would fail if VACUUM had already removed the toast tuples. Easiest fix is to get rid of the special case for xmin == xmax. This may delay reclaiming dead space for a little bit in some cases, but it's by far the most reliable way to fix the issue. Per bug #5998 from Mark Reid. Back-patch to 8.3, which is the oldest version with MVCC-safe CLUSTER. |
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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/.