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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 |
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