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This parameter is turned on by default and starts automatic relay log recovery immediately after the database is started. During the recovery process, create a new relay log and initialize the IO thread to the location of the SQL thread.

During the operation of MySQL, if there is a downtime, it must be able to recover to the location where the transaction has been executed after starting the library. This information is traditionally stored in the file, so there may be a risk of inconsistency or corruption for a long time. Starting with MySQL5.7, you can use tables to store this information, concurrently these tables are set as InnoDB engines, and recover this information by using a transactional storage engine. You can configure the parameters master_info_repository=table and relay_log_info_repository=table to store slave library information in a table. How the library recovers from the down state to the correct state depends on whether the slave library is single-threaded or multithreaded, the value of the relay_log_recover parameter, and how master_auto_position is used.

1. Replication in single-thread mode

1) when replication is based on GTID mode, and the master_auto_position parameter and relay_log_recover=0 are set, using this configuration, the settings of relay_log_info_repository and other variables will not affect the recovery.

2) when based on the traditional mode (file position), set relay_log_recover=1 and relay_log_info_repository=table.

2. Replication of multithreading mode

1) when replication is based on GTID mode, and master_auto_position and relay_log_recovery=0 are set, using this configuration, the settings of relay_log_info_reposition and other variables will not affect the recovery.

2) when replicating based on traditional mode, set relay_log_recovery=1, sync_relay_log=1, and relay_log_info_repository=table.

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