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Previously if hot standby was enabled, archive recovery exited with an error when it found WAL generated with wal_level=minimal. But if hot standby was disabled, it just reported a warning and continued in that case. Which could lead to data loss or errors during normal operation. A warning was emitted, but users could easily miss that and not notice this serious situation until they encountered the actual errors. To improve this situation, this commit changes archive recovery so that it exits with FATAL error when it finds WAL generated with wal_level=minimal whatever the setting of hot standby. This enables users to notice the serious situation soon. The FATAL error is thrown if archive recovery starts from a base backup taken before wal_level is changed to minimal. When archive recovery exits with the error, if users have a base backup taken after setting wal_level to higher than minimal, they can recover the database by starting archive recovery from that newer backup. But note that if such backup doesn't exist, there is no easy way to complete archive recovery, which may make the database server unstartable and users may lose whole database. The commit adds the note about this risk into the document. Even in the case of unstartable database server, previously by just disabling hot standby users could avoid the error during archive recovery, forcibly start up the server and salvage data from it. But note that this commit makes this procedure unavailable at all. Author: Takamichi Osumi Reviewed-by: Laurenz Albe, Kyotaro Horiguchi, David Steele, Fujii Masao Discussion: https://postgr.es/m/OSBPR01MB4888CBE1DA08818FD2D90ED8EDF90@OSBPR01MB4888.jpnprd01.prod.outlook.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/.