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When certain parameters are changed on a physical replication primary, this is communicated to standbys using the XLOG_PARAMETER_CHANGE WAL record. The standby then checks whether its own settings are at least as big as the ones on the primary. If not, the standby shuts down with a fatal error. The correspondence of settings between primary and standby is required because those settings influence certain shared memory sizings that are required for processing WAL records that the primary might send. For example, if the primary sends a prepared transaction, the standby must have had max_prepared_transaction set appropriately or it won't be able to process those WAL records. However, fatally shutting down the standby immediately upon receipt of the parameter change record might be a bit of an overreaction. The resources related to those settings are not required immediately at that point, and might never be required if the activity on the primary does not exhaust all those resources. If we just let the standby roll on with recovery, it will eventually produce an appropriate error when those resources are used. So this patch relaxes this a bit. Upon receipt of XLOG_PARAMETER_CHANGE, we still check the settings but only issue a warning and set a global flag if there is a problem. Then when we actually hit the resource issue and the flag was set, we issue another warning message with relevant information. At that point we pause recovery, so a hot standby remains usable. We also repeat the last warning message once a minute so it is harder to miss or ignore. Reviewed-by: Sergei Kornilov <sk@zsrv.org> Reviewed-by: Masahiko Sawada <masahiko.sawada@2ndquadrant.com> Reviewed-by: Kyotaro Horiguchi <horikyota.ntt@gmail.com> Discussion: https://www.postgresql.org/message-id/flat/4ad69a4c-cc9b-0dfe-0352-8b1b0cd36c7b@2ndquadrant.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/.