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Sometimes it happens that the visibility information for a tuple becomes corrupted, either due to bugs in the database software or external factors. Provide a function heap_force_kill() that can be used to truncate such dead tuples to dead line pointers, and a function heap_force_freeze() that can be used to overwrite the visibility information in such a way that the tuple becomes all-visible. These functions are unsafe, in that you can easily use them to corrupt a database that was not previously corrupted, and you can use them to further corrupt an already-corrupted database or to destroy data. The documentation accordingly cautions against casual use. However, in some cases they permit recovery of data that would otherwise be very difficult to recover, or to allow a system to continue to function when it would otherwise be difficult to do so. Because we may want to add other functions for performing other kinds of surgery in the future, the new contrib module is called pg_surgery rather than something specific to these functions. I proposed back-patching this so that it could be more easily used by people running existing releases who are facing these kinds of problems, but that proposal did not attract enough support, so no back-patch for now. Ashutosh Sharma, reviewed and tested by Andrey M. Borodin, M. Beena Emerson, Masahiko Sawada, Rajkumar Raghuwanshi, Asim Praveen, and Mark Dilger, and somewhat revised by me. Discussion: http://postgr.es/m/CA+TgmoZW1fsU-QUNCRUQMGUygBDPVeOTLCqRdQZch=EYZnctSA@mail.gmail.com |
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README
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: https://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. 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 https://www.postgresql.org/download/. For more information look at our web site located at https://www.postgresql.org/.