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16.2.3 How Servers Evaluate Replication Filtering Rules »
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16.2.2.2. The Slave Status Files

A slave replication server creates two small status files. By default, these files are named master.info and relay-log.info and created in the data directory. Their names and locations can be changed by using the --master-info-file and --relay-log-info-file options (see Section 16.1.3, “Replication and Binary Logging Options and Variables”).

The two status files contain information like that shown in the output of the SHOW SLAVE STATUS statement, which is discussed in Section 12.5.2, “SQL Statements for Controlling Slave Servers”. Because the status files are stored on disk, they survive a slave server's shutdown. The next time the slave starts up, it reads the two files to determine how far it has proceeded in reading binary logs from the master and in processing its own relay logs.

The master.info file should be protected because it contains the password for connecting to the master. See Section 5.3.2.1, “Administrator Guidelines for Password Security”.

The I/O thread updates the master.info file. The following table shows the correspondence between the lines in the file and the columns displayed by SHOW SLAVE STATUS.

Line Status Column Description
1   Number of lines in the file
2 Master_Log_File The name of the master binary log currently being read from the master
3 Read_Master_Log_Pos The current position within the master binary log that have been read from the master
4 Master_Host The host name of the master
5 Master_User The user name used to connect to the master
6 Password (not shown by SHOW SLAVE STATUS) The password used to connect to the master
7 Master_Port The network port used to connect to the master
8 Connect_Retry The period (in seconds) that the slave will wait before trying to reconnect to the master
9 Master_SSL_Allowed Indicates whether the server supports SSL connections
10 Master_SSL_CA_File The file used for the Certificate Authority (CA) certificate
11 Master_SSL_CA_Path The path to the Certificate Authority (CA) certificates
12 Master_SSL_Cert The name of the SSL certificate file
13 Master_SSL_Cipher The name of the cipher in use for the SSL connection
14 Master_SSL_Key The name of the SSL key file
15 Master_SSL_Verify_Server_Cert Whether to verify the server certificate
17 Replicate_Ignore_Server_Ids The number of server IDs to be ignored, followed by the actual server IDs

The SQL thread updates the relay-log.info file. The following table shows the correspondence between the lines in the file and the columns displayed by SHOW SLAVE STATUS.

Line Status Column Description
1 Relay_Log_File The name of the current relay log file
2 Relay_Log_Pos The current position within the relay log file; events up to this position have been executed on the slave database
3 Relay_Master_Log_File The name of the master binary log file from which the events in the relay log file were read
4 Exec_Master_Log_Pos The equivalent position within the master's binary log file of events that have already been executed

The contents of the relay-log.info file and the states shown by the SHOW SLAVE STATUS statement might not match if the relay-log.info file has not been flushed to disk. Ideally, you should only view relay-log.info on a slave that is offline (that is, mysqld is not running). For a running system, SHOW SLAVE STATUS should be used.