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The old documentation encourages entering single-user mode for no reason, which is a bad plan in most cases. Instead, discourage users from doing that, and explain the limited cases in which it may be desirable. The old documentation claims that running VACUUM as anyone but the superuser can't possibly work, which is not really true, because it might be that some other user has enough permissions to VACUUM all the tables that matter. Weaken the language just a bit. The old documentation claims that you can't run any commands when near XID exhaustion, which is false because you can still run commands that don't require an XID, like a SELECT without a locking clause. The old documentation doesn't clearly explain that it's a good idea to get rid of prepared transactons, long-running transactions, and replication slots that are preventing (M)XID horizon advancement. Spell out the steps to do that. Also, discourage the use of VACUUM FULL and VACUUM FREEZE in this type of scenario. Back-patch to v14. Much of this is good advice on all supported versions, but before 60f1f09ff44308667ef6c72fbafd68235e55ae27 the chances of VACUUM failing in multi-user mode were much higher. Alexander Alekseev, John Naylor, Robert Haas, reviewed at various times by Peter Geoghegan, Hannu Krosing, and Andres Freund. Discussion: http://postgr.es/m/CA+TgmoYtsUDrzaHcmjFhLzTk1VEv29mO_u-MT+XWHrBJ_4nD8A@mail.gmail.com
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/.