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12.5.5.36. SHOW SLAVE STATUS Syntax

SHOW SLAVE STATUS

This statement provides status information on essential parameters of the slave threads. It requires either the SUPER or REPLICATION CLIENT privilege.

If you issue this statement using the mysql client, you can use a \G statement terminator rather than a semicolon to obtain a more readable vertical layout: 

mysql> SHOW SLAVE STATUS\G
*************************** 1. row ***************************
               Slave_IO_State: Waiting for master to send event
                  Master_Host: localhost
                  Master_User: root
                  Master_Port: 3306
                Connect_Retry: 3
              Master_Log_File: gbichot-bin.005
          Read_Master_Log_Pos: 79
               Relay_Log_File: gbichot-relay-bin.005
                Relay_Log_Pos: 548
        Relay_Master_Log_File: gbichot-bin.005
             Slave_IO_Running: Yes
            Slave_SQL_Running: Yes
              Replicate_Do_DB:
          Replicate_Ignore_DB:
                   Last_Errno: 0
                   Last_Error:
                 Skip_Counter: 0
          Exec_Master_Log_Pos: 79
              Relay_Log_Space: 552
              Until_Condition: None
               Until_Log_File:
                Until_Log_Pos: 0
           Master_SSL_Allowed: No
           Master_SSL_CA_File:
           Master_SSL_CA_Path:
              Master_SSL_Cert:
            Master_SSL_Cipher:
               Master_SSL_Key:
        Seconds_Behind_Master: 8
Master_SSL_Verify_Server_Cert: No
                Last_IO_Errno: 0
                Last_IO_Error:
               Last_SQL_Errno: 0
               Last_SQL_Error:

SHOW SLAVE STATUS returns the following fields:

  • Slave_IO_State

    A copy of the State field of the output of SHOW PROCESSLIST for the slave I/O thread. This tells you what the thread is doing: trying to connect to the master, waiting for events from the master, reconnecting to the master, and so on. Possible states are listed in Section 16.4.1, “Replication Implementation Details”. It is necessary to check this field for older versions of MySQL which allowed the thread to continue running while unsuccessfully trying to connect to the master. If it is running, there is no problem; if it is not, you can find the error in the Last_Error field (described below).

  • Master_Host

    The current master host.

  • Master_User

    The current user used to connect to the master.

  • Master_Port

    The current master port.

  • Connect_Retry

    The number of seconds between connect retries (default 60). This may be set with the CHANGE MASTER TO statement or --master-connect-retry option.

  • Master_Log_File

    The name of the master binary log file from which the I/O thread is currently reading.

  • Read_Master_Log_Pos

    The position up to which the I/O thread has read in the current master binary log.

  • Relay_Log_File

    The name of the relay log file from which the SQL thread is currently reading and executing.

  • Relay_Log_Pos

    The position up to which the SQL thread has read and executed in the current relay log.

  • Relay_Master_Log_File

    The name of the master binary log file containing the most recent event executed by the SQL thread.

  • Slave_IO_Running

    Whether the I/O thread is started and has connected successfully to the master. Internally, the state of this thread is represented by one of 3 values; these are shown with their meanings in the following list:

    • MYSQL_SLAVE_NOT_RUN.  The slave I/O thread is not running.

    • MYSQL_SLAVE_RUN_NOT_CONNECT.  The slave I/O thread is running, but is not connected to a replication master.

    • MYSQL_SLAVE_RUN_CONNECT.  The slave I/O thread is running, and is connected to a replication master.

    Different values are displayed for Slave_IO_running depending on the slave I/O thread's actual state and the version of MySQL used on the replication slave, as shown in the following table.

    MySQL Version MYSQL_SLAVE_NOT_RUN MYSQL_SLAVE_RUN_NOT_CONNECT MYSQL_SLAVE_RUN_CONNECT
    4.1 (4.1.13 and earlier); 5.0 (5.0.11 and earlier) No Yes Yes
    4.1 (4.1.14 and later); 5.0 (5.0.12 and later) No No Yes
    5.1; 5.4 (5.4.3 and earlier) No No Yes
    5.4 (5.4.4 and later) No Connecting Yes

  • Slave_SQL_Running

    Whether the SQL thread is started.

  • Replicate_Do_DB, Replicate_Ignore_DB

    The lists of databases that were specified with the --replicate-do-db and --replicate-ignore-db options, if any.

  • Replicate_Do_Table, Replicate_Ignore_Table, Replicate_Wild_Do_Table, Replicate_Wild_Ignore_Table

    The lists of tables that were specified with the --replicate-do-table, --replicate-ignore-table, --replicate-wild-do-table, and --replicate-wild-ignore-table options, if any.

  • Last_Errno, Last_Error

    As of MySQL 5.1.20, these columns are aliases for Last_SQL_Errno and Last_SQL_Error. Before 5.1.20, they indicate the error number and error message returned by the most recently executed statement. An error number of 0 and message of the empty string mean “no error.” If the Last_Error value is not empty, it also appears as a message in the slave's error log.

    Beginning with MySQL 5.1.37, and with MySQL Cluster NDB 6.2.17, MySQL Cluster NDB 6.3.23, and MySQL Cluster NDB 6.4.3: Issuing RESET MASTER or RESET SLAVE resets the values shown in these columns. (Bug#34654, Bug#44270)

    Note

    When the slave SQL thread receives an error, it reports the error first, then stops the SQL thread. This means that there is a small window of time during which SHOW SLAVE STATUS shows a nonzero value for Last_Errno even though Slave_SQL_Running still displays Yes.

  • Skip_Counter

    The most recently used value for SQL_SLAVE_SKIP_COUNTER.

  • Exec_Master_Log_Pos

    The position of the last event executed by the SQL thread from the master's binary log (Relay_Master_Log_File). (Relay_Master_Log_File, Exec_Master_Log_Pos) in the master's binary log corresponds to (Relay_Log_File, Relay_Log_Pos) in the relay log.

  • Relay_Log_Space

    The total combined size of all existing relay logs.

  • Until_Condition, Until_Log_File, Until_Log_Pos

    The values specified in the UNTIL clause of the START SLAVE statement.

    Until_Condition has these values:

    • None if no UNTIL clause was specified

    • Master if the slave is reading until a given position in the master's binary logs

    • Relay if the slave is reading until a given position in its relay logs

    Until_Log_File and Until_Log_Pos indicate the log file name and position values that define the point at which the SQL thread stops executing.

  • Master_SSL_Allowed, Master_SSL_CA_File, Master_SSL_CA_Path, Master_SSL_Cert, Master_SSL_Cipher, Master_SSL_Key

    These fields show the SSL parameters used by the slave to connect to the master, if any.

    Master_SSL_Allowed has these values:

    • Yes if an SSL connection to the master is permitted

    • No if an SSL connection to the master is not permitted

    • Ignored if an SSL connection is permitted but the slave server does not have SSL support enabled

    The values of the other SSL-related fields correspond to the values of the MASTER_SSL_CA, MASTER_SSL_CAPATH, MASTER_SSL_CERT, MASTER_SSL_CIPHER, MASTER_SSL_KEY, and MASTER_SSL_VERIFY_SERVER_CERT options to the CHANGE MASTER TO statement. See Section 12.6.2.1, “CHANGE MASTER TO Syntax”. MASTER_SSL_VERIFY_SERVER_CERT was added in MySQL 5.1.18.

  • Seconds_Behind_Master

    This field is an indication of how “late” the slave is:

    • When the slave SQL thread is actively running (processing updates), this field is the number of seconds that have elapsed since the timestamp of the most recent event on the master executed by that thread.

    • When the SQL thread has caught up to the slave I/O thread and goes idle waiting for more events from the I/O thread, this field is zero.

    In essence, this field measures the time difference in seconds between the slave SQL thread and the slave I/O thread.

    If the network connection between master and slave is fast, the slave I/O thread is very close to the master, so this field is a good approximation of how late the slave SQL thread is compared to the master. If the network is slow, this is not a good approximation; the slave SQL thread may quite often be caught up with the slow-reading slave I/O thread, so Seconds_Behind_Master often shows a value of 0, even if the I/O thread is late compared to the master. In other words, this column is useful only for fast networks.

    This time difference computation works even though the master and slave do not have identical clocks (the clock difference is computed when the slave I/O thread starts, and assumed to remain constant from then on). Seconds_Behind_Master is NULL (which means “unknown”) if the slave SQL thread is not running, or if the slave I/O thread is not running or not connected to master. For example if the slave I/O thread is sleeping for the number of seconds given by the CHANGE MASTER TO statement or --master-connect-retry option (default 60) before reconnecting, NULL is shown, as the slave cannot know what the master is doing, and so cannot say reliably how late it is.

    This field has one limitation. The timestamp is preserved through replication, which means that, if a master M1 is itself a slave of M0, any event from M1's binlog which originates in replicating an event from M0's binlog has the timestamp of that event. This enables MySQL to replicate TIMESTAMP successfully. However, the problem for Seconds_Behind_Master is that if M1 also receives direct updates from clients, the value randomly deviates, because sometimes the last M1's event is from M0 and sometimes it is the most recent timestamp from a direct update.

  • Last_IO_Errno, Last_IO_Error

    The error number and error message of the last error that caused the I/O thread to stop. An error number of 0 and message of the empty string mean “no error.” If the Last_IO_Error value is not empty, it also appears as a message in the slave's error log. These columns were added in MySQL 5.1.20.

    MySQL Cluster.  Beginning with MySQL Cluster NDB 6.2.17, 6.3.23, and 6.4.3: Issuing RESET MASTER or RESET SLAVE resets the values shown in these columns. This applies to MySQL Cluster only. (Bug#34654)

  • Last_SQL_Errno, Last_SQL_Error

    The error number and error message of the last error that caused the SQL thread to stop. An error number of 0 and message of the empty string mean “no error.” If the Last_IO_Error value is not empty, it also appears as a message in the slave's error log. These columns were added in MySQL 5.1.20.

    Example: 

    Last_SQL_Errno: 1051
Last_SQL_Error: error 'Unknown table 'z'' on query 'drop table z'

    The message indicates that the table z existed on the master and was dropped there, but it did not exist on the slave, so DROP TABLE failed on the slave. (This might occur, for example, if you forget to copy the table to the slave when setting up replication.)

    MySQL Cluster.  Beginning with MySQL Cluster NDB 6.2.17, 6.3.23, and 6.4.3: Issuing RESET MASTER or RESET SLAVE resets the values shown in these columns. This applies to MySQL Cluster only. (Bug#34654)


User Comments

Posted by Johannes Ullrich on October 31 2006 1:53pm[Delete] [Edit]

Between different versions of mysql, the capitalization of the column names chagned. Careful if you write your own scripts around this.

Posted by Rachel McConnell on September 10 2009 7:21pm[Delete] [Edit]

If you find your slave status to show this:

Slave_IO_State: Connecting to Master
...
Slave_IO_Running: No
Slave_SQL_Running: Yes
...

and replication is not happening, your problem may be the slave configuration is wrong. Either the log file name is incorrect, or the replication user's password is wrong, are probably the most common cases. There doesn't seem to be any error message shown anywhere, but you can try these things. Check the file names by SHOW MASTER STATUS on the master, and doublecheck it against the master.info file on the slave. For the password, you can issue a new GRANT statement on the master, and a matching CHANGE MASTER statement on the slave, to be sure they are the same.

Posted by Alexey Zilber on October 6 2009 11:35pm[Delete] [Edit]

Here's a quick php code snippet to read your master.info and relay-log.info and generate a change master sql command from it. Very useful if you get corrupted relay logs or have had to purge your relay logs, etc.

<?php
$master_info=array();
$relay_info=array();
$x=0;
$mi=fopen('/tmp/master.info','r'); //<-- replace
$ri=fopen('/tmp/relay-log.info','r'); //<-- replace

if($mi){
        while(!feof($mi)){
        $master_info[$x]=chop(fgets($mi,512));
        $x++;
        }
        fclose($mi);
}

$x=0;
if($ri){
        while(!feof($ri)){
        $relay_info[$x]=chop(fgets($ri,512));
        $x++;
        }
        fclose($ri);
}

$x=0;
echo "CHANGE MASTER TO MASTER_HOST='$master_info[3]',MASTER_USER='$master_info[4]', MASTER_PASSWORD='$master_info[5]', MASTER_LOG_FILE='$relay_info[2]', MASTER_LOG_POS=$relay_info[3];";

exit(0);
?>

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