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• rpl_read_size 

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The rpl_read_size  system variable controls the minimum amount of data in bytes that is read from the binary log files and relay log files. If heavy disk I/O activity for these files is impeding performance for the database, increasing the read size might reduce file reads and I/O stalls when the file data is not currently cached by the operating system. 

The minimum and default value for rpl_read_size  is 8192 bytes. The value must be a multiple of 4KB. Note that a buffer the size of this value is allocated for each thread that reads from the binary log and relay log files, including dump threads on sources and coordinator threads on replicas. Setting a large value might therefore have an impact on memory consumption for servers. 

• rpl_semi_sync_slave_enabled 

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Controls whether semisynchronous replication is enabled on the replica server. To enable or disable the plugin, set this variable to ON  or OFF  (or 1 or 0), respectively. The default is OFF . 

This variable is available only if the replica-side semisynchronous replication plugin is installed. 

• rpl_semi_sync_slave_trace_level 

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