Oracle 5.0 Reference Manual page 1217

• When the slave SQL thread is actively 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 is 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
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 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
calculation of
This field is
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
CHANGE MASTER TO
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
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
is that if M1 also receives direct updates from clients, the
randomly fluctuates because sometimes the last event from M1 originates from M0 and sometimes is
the result of a direct update on M1.
13.7.5.32.
SHOW STATUS
SHOW [GLOBAL | SESSION] STATUS
[LIKE 'pattern' | WHERE expr]
SHOW STATUS
the
mysqladmin extended-status
which variable names to match. The
conditions, as discussed in
require any privilege. It requires only the ability to connect to the server.
Partial output is shown here. The list of names and values may be different for your server. The
meaning of each variable is given in
mysql> SHOW STATUS;
+--------------------------+------------+
| Variable_name
+--------------------------+------------+
| Aborted_clients
| Aborted_connects
| Bytes_received
| Bytes_sent
| Connections
| Created_tmp_disk_tables
| Created_tmp_tables
Seconds_Behind_Master
(undefined or unknown) if the slave SQL thread is not running, or if the slave I/
NULL
statement or
Seconds_Behind_Master
successfully. However, the problem for
TIMESTAMP
Syntax
provides server status information. This information also can be obtained using
WHERE
Section 19.18, "Extensions to
Section 5.1.6, "Server Status
| Value
| 0
| 0
| 155372598
| 1176560426 |
| 30023
| 0
| 8340
Syntax
SHOW
Seconds_Behind_Master
less reliable.
--master-connect-retry
is based on the timestamps stored in events, which are
Seconds_Behind_Master
command. The
LIKE
clause can be given to select rows using more general
SHOW
|
|
|
|
|
|
|
1197
[1453] option (default 60) before
Seconds_Behind_Master
[896] clause, if present, indicates
Statements". This statement does not
Variables".
often shows a
value