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This oversight led to data corruption in matviews, manifesting as "could not access status of transaction" before our most recent releases, and "found xmin from before relfrozenxid" errors since then. The proximate cause of the problem seems to have been confusion between the task of preserving dropped-column status and the task of preserving frozenxid status. Those are required for distinct sets of relkinds, and the reasoning was entirely undocumented in the source code. In hopes of forestalling future errors of the same kind, try to improve the commentary in this area. In passing, also improve the remarkably unhelpful comments around pg_upgrade's set_frozenxids(). That's not actually buggy AFAICS, but good luck figuring out what it does from the old comments. Per report from Claudio Freire. It appears that bug #14852 from Alexey Ermakov is an earlier report of the same issue, and there may be other cases that we failed to identify at the time. Patch by me based on analysis by Andres Freund. The bug dates back to the introduction of matviews, so back-patch to all supported branches. Discussion: https://postgr.es/m/CAGTBQpbrY9CdRGGhyBZ9yqY4jWaGC85rUF4X+R7d-aim=mBNsw@mail.gmail.com Discussion: https://postgr.es/m/20171013115320.28049.86457@wrigleys.postgresql.org
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/.