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did not expect that a DEAD tuple could follow a RECENTLY_DEAD tuple in an update chain, but because the OldestXmin rule for determining deadness is a simplification of reality, it is possible for this situation to occur (implying that the RECENTLY_DEAD tuple is in fact dead to all observers, but this patch does not attempt to exploit that). The code would follow a chain forward all the way, but then stop before a DEAD tuple when backing up, meaning that not all of the chain got moved. This could lead to copying the chain multiple times (resulting in duplicate copies of the live tuple at its end), or leaving dangling index entries behind (which, aside from generating warnings from later vacuums, creates a risk of wrong query results or bogus duplicate-key errors once the heap slot the index entry points to is repopulated). The fix is to recheck HeapTupleSatisfiesVacuum while following a chain forward, and to stop if a DEAD tuple is reached. Each contiguous group of RECENTLY_DEAD tuples will therefore be copied as a separate chain. The patch also adds a couple of extra sanity checks to verify correct behavior. Per report and test case from Pavan Deolasee.
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. The JDBC, ODBC, C++, Python, and Tcl interfaces have been moved to the PostgreSQL Projects Web Site at http://gborg.postgresql.org for separate maintenance. A Perl DBI/DBD driver is available from CPAN. 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 ftp://ftp.postgresql.org/pub/. For more information look at our web site located at http://www.postgresql.org/.