SHOW SLAVE STATUS
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
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: Replicate_Do_Table: Replicate_Ignore_Table: Replicate_Wild_Do_Table: Replicate_Wild_Ignore_Table: 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
A copy of the
State field of the
SHOW PROCESSLIST output 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. For
a listing of possible states, see
Section 8.10.6, “Replication Slave I/O Thread States”. For versions of
MySQL prior to 5.0.12, it is necessary to check this field
for connection problems. In those versions, the thread could
be running while unsuccessfully trying to connect to the
master; only this field makes you aware of the problem. The
state of the SQL thread is not copied because it is simpler.
If it is running, there is no problem; if it is not, you can
find the error in the
The master host that the slave is connected to.
The user name of the account used to connect to the master.
The port used to connect to the master.
The name of the master binary log file from which the I/O thread is currently reading.
The position in the current master binary log file up to which the I/O thread has read.
The name of the relay log file from which the SQL thread is currently reading and executing.
The position in the current relay log file up to which the SQL thread has read and executed.
The name of the master binary log file containing the most recent event executed by the SQL thread.
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 the following three values:
The slave I/O thread is not running. For this state,
The slave I/O thread is running, but is not connected
to a replication master. For this state,
Slave_IO_Running depends on the
server version as shown in the following table.
|4.1 (4.1.13 and earlier); 5.0 (5.0.11 and earlier)|
|4.1 (4.1.14 and later); 5.0 (5.0.12 and later)|
The slave I/O thread is running, and is connected to a
replication master. For this state,
Whether the SQL thread is started.
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
Last_Error value is not empty, it
also appears as a message in the slave's error log. For
Last_Errno: 1051 Last_Error: error 'Unknown table 'z'' on query 'drop table z'
The message indicates that the table
existed on the master and was dropped there, but it did not
exist on the slave, so
TABLE failed on the slave. (This might occur, for
example, if you forget to copy the table to the slave when
setting up replication.)
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
Slave_SQL_Running still displays
The current value of the
system variable. See
Section 126.96.36.199, “SET GLOBAL sql_slave_skip_counter Syntax”.
The position in the current master binary log file to which
the SQL thread has read and executed, marking the start of
the next transaction or event to be processed. You can use
this value with the
MASTER_LOG_POS option when starting a new
slave from an existing slave, so that the new slave reads
from this point. The coordinates given by
Exec_Master_Log_Pos) in the master's
binary log correspond to the coordinates given by
Relay_Log_Pos) in the relay log.
The total combined size of all existing relay log files.
The values specified in the
START SLAVE statement.
Until_Condition has these values:
None if no
clause was specified
Master if the slave is reading until
a given position in the master's binary log
Relay if the slave is reading until a
given position in its relay log
Until_Log_Pos indicate the log file name
and position that define the coordinates at which the SQL
thread stops executing.
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
The values of the other SSL-related fields correspond to the
values of the
MASTER_SSL_KEY options to the
CHANGE MASTER TO statement.
See Section 188.8.131.52, “CHANGE MASTER TO Syntax”.
This field is an indication of how “late” the slave is:
When the slave is actively processing updates, this field shows the difference between the current timestamp on the slave and the original timestamp logged on the master for the event currently being processed on the slave.
When no event is currently being processed on the slave, this value is 0.
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
This time difference computation works even if the master
and slave do not have identical clock times, provided that
the difference, computed when the slave I/O thread starts,
remains constant from then on. Any changes—including
NTP updates—can lead to clock skews that can make
This field is
NULL (undefined or unknown)
if the slave SQL thread is not running, or if the slave I/O
thread is not running or is not connected to the master. For
example, if the slave I/O thread is running but is not
connected to the master and is sleeping for the number of
seconds given by the
TO statement or
(default 60) before reconnecting, the value is
NULL. This is because the slave cannot
know what the master is doing, and so cannot say reliably
how late it is.
The value of
based on the timestamps stored in events, which are
preserved through replication. This means that if a master
M1 is itself a slave of M0, any event from M1's binary log
that originates from M0's binary log has M0's timestamp for
that event. This enables MySQL to replicate
However, the problem for
Seconds_Behind_Master is that if M1 also
receives direct updates from clients, the
Seconds_Behind_Master value randomly
fluctuates because sometimes the last event from M1
originates from M0 and sometimes is the result of a direct
update on M1.