6.24 Replication Slave Activity Metrics

Lists the Replication Slave Activity metrics and provides a brief description of each.

Table 6.24 Replication Slave Activity Metrics

Name	Description
Change Master (Delta)	The total number of CHANGE MASTER statements executed.
Exec Master Log Pos	The position in the current master binary file up to which the SQL thread has read and executed.
Executed Gtid Set	The set of global transaction IDs for all received transactions subsequently executed on this slave. Empty if GTIDs are not in use.
Heartbeat Period	The replication heartbeat interval (in seconds) for the slave.
IO Running	Whether the slave I/O thread is started and has connected successfully to the master.
IO State	The current informational state for the slave I/O thread.
Last Errno	The error number of the last error that caused the SQL thread to stop.
Last Error	The error message of the last error that caused the SQL thread to stop.
Last IO Errno	The error number of the last error that caused the I/O thread to stop.
Last IO Error	The error message of the last error that caused the I/O thread to stop.
Last SQL Errno	The error number of the last error that caused the SQL thread to stop.
Last SQL Error	The error message of the last error that caused the SQL thread to stop.
Master Log File	The name of the master binary log file from which the I/O thread is currently reading.
Open Temp Tables	The number of temporary tables that the slave SQL thread currently has open.
Read Master Log Pos	The position in the current master binary log file up to which the I/O thread has read.
Received Heartbeats (Delta)	The total number of heartbeats received by the slave since the last time that the slave was restarted or reset, or a CHANGE MASTER TO statement was issued.
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 in the current relay log file up to which the SQL thread has read and executed.
Relay Log Space	The total combined size of all existing relay log files.
Relay Master Log File	The name of the master binary log file containing the most recent event executed by the SQL thread.
Retried Transactions (Delta)	The total number of times since startup that the replication slave SQL thread has retried transactions.
Retrieved Gtid Set	The set of global transaction IDs corresponding to all transactions received by this slave. Empty if GTIDs are not in use.
Running	This is ON if this server is a replication slave that is connected to a replication master, and both the I/O and SQL threads are running; otherwise, it is OFF.
Seconds Behind Master	The time difference in seconds between the slave SQL thread and the slave I/O thread, based on the timestamps stored in the relay log events. NULL if the slave SQL thread is not running, or if the slave I/O thread is not running or not connected to the master.
Semi Sync Slave Status	Whether semisynchronous replication currently is operational on the slave. This is ON if the plugin has been enabled and the slave I/O thread is running, OFF otherwise.
Show Slave Status (Delta)	The total number of SHOW SLAVE STATUS statements executed.
Skip Counter	The current value of the sql_slave_skip_counter system variable.
Slave Start (Delta)	The total number of START SLAVE statements executed.
Slave Stop (Delta)	The total number of STOP SLAVE statements executed.
SQL Remaining Delay	The number of seconds before the slave SQL thread will apply the next event within the relay logs.
SQL Running	Whether the slave SQL thread is started.
SQL Running State	The current informational state for the slave SQL thread.
Slave Error: Unknown or Incorrect Time Zone	In order to use time zone names in conjunction with certain statements, functions, and data types, you must configure the server to understand those names by loading information from the operating system's time zone files into a set of tables in the mysql database. However, while the MySQL installation procedure creates those time zone tables, it does not load them; they must be loaded manually after installation.
Slave Execution Position Behind Read Position	When a slave receives updates from its master, the I/O thread stores the data in local files known as relay logs. The slave's SQL thread reads the relay logs and executes the updates they contain. If the position from which the SQL thread is reading is way behind the position to which the I/O thread is currently writing, it is a sign that replication is getting behind and results of queries directed to the slave may not reflect the latest changes made on the master.
Slave Has Been Stopped	If replication on a slave has been stopped, it means the slave is not retrieving the latest statements from the master and it is not executing those statements on the slave.
Slave Has Experienced A Replication Error	When a slave receives updates from its master it must apply those updates locally so the data on the slave matches that on the server. If an error occurs while applying an update on a slave, the data on the slave may not match that on the master and it is an indication that replication may be broken.
Slave Has Problem Communicating With Master	Slaves must connect to a master to get the latest data from the master. If they cannot connect, or periodically have trouble connecting, replication may fall behind (i.e. the slave may not have the latest data that was written to the master).
Slave Has Stopped Replicating	If neither the slave I/O thread nor the slave SQL threads are running, it means the slave is not getting the latest statements from the master and it is not executing those statements on the slave, and thus replication has stopped entirely.
Slave I/O Thread Not Running	The slave I/O thread is the thread that retrieves statements from the master's binary log and records them into the slave's relay log. If this thread isn't running, it means the slave is not able to retrieve the latest data from the master.
Slave Relay Log Space	When a slave receives updates from its master, the I/O thread stores the data in local files known as relay logs. The slave's SQL thread reads the relay logs and executes the updates they contain. After the SQL thread has executed all the updates in a relay log, the file is no longer needed and can be deleted to conserve disk space.
Slave SQL Thread Not Running	The slave SQL thread is the thread that reads statements from the slave's relay log and executes them to bring the slave in sync with the master. If this thread isn't running, it means the slave is not able to apply the latest changes it has read from the master, and results of queries directed to the slave may not reflect the latest changes made on the master.
Slave Seconds Behind Master	If a slave is too far behind the master, results of queries directed to the slave may not reflect the latest changes made on the master.
Slave Waiting To Free Relay Log Space	For slaves with limited disk space you can place a limit on how large the replication relay log can grow. When the limit is reached, the I/O thread stops reading binary log events from the master server until the SQL thread has caught up and deleted some unprocessed relay logs. While this protects MySQL from filling up the disk, it means replication is delayed and the slave will fall behind the master.