6.27 Replication Replica Activity Metrics

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

Table 6.27 Replication Replica Activity Metrics

Name	Description
Change Source (Delta)	The total number of CHANGE SOURCE statements executed.
Exec Source Log Pos	The position in the current source 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 replica. Empty if GTIDs are not in use.
Heartbeat Period	The replication heartbeat interval (in seconds) for the replica.
IO Running	Whether the replica I/O thread is started and has connected successfully to the source.
IO State	The current informational state for the replica 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.
Source Log File	The name of the source binary log file from which the I/O thread is currently reading.
Open Temp Tables	The number of temporary tables that the replica SQL thread currently has open.
Read Source Log Pos	The position in the current source binary log file up to which the I/O thread has read.
Received Heartbeats (Delta)	The total number of heartbeats received by the replica since the last time that the replica was restarted or reset, or a CHANGE SOURCE 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 Source Log File	The name of the source 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 replica SQL thread has retried transactions.
Retrieved Gtid Set	The set of global transaction IDs corresponding to all transactions received by this replica. Empty if GTIDs are not in use.
Running	This is ON if this server is a replication replica that is connected to a replication source, and both the I/O and SQL threads are running; otherwise, it is OFF.
Seconds Behind Source	The time difference in seconds between the replica SQL thread and the replica I/O thread, based on the timestamps stored in the relay log events. NULL if the replica SQL thread is not running, or if the replica I/O thread is not running or not connected to the source.
Semi Sync Replica Status	Whether semisynchronous replication currently is operational on the replica. This is ON if the plugin has been enabled and the replica I/O thread is running, OFF otherwise.
Show Replica Status (Delta)	The total number of SHOW REPLICA STATUS statements executed.
Skip Counter	The current value of the sql_replica_skip_counter system variable.
Replica Start (Delta)	The total number of START REPLICA statements executed.
Replica Stop (Delta)	The total number of STOP REPLICA statements executed.
SQL Remaining Delay	The number of seconds before the replica SQL thread will apply the next event within the relay logs.
SQL Running	Whether the replica SQL thread is started.
SQL Running State	The current informational state for the replica SQL thread.
Replica 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.
Replica Execution Position Behind Read Position	When a replica receives updates from its source, the I/O thread stores the data in local files known as relay logs. The replica'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 replica may not reflect the latest changes made on the source.
Replica Has Been Stopped	If replication on a replica has been stopped, it means the replica is not retrieving the latest statements from the source and it is not executing those statements on the replica.
Replica Has Experienced A Replication Error	When a replica receives updates from its source it must apply those updates locally so the data on the replica matches that on the server. If an error occurs while applying an update on a replica, the data on the replica may not match that on the source and it is an indication that replication may be broken.
Replica Has Problem Communicating With Source	Replicas must connect to a source to get the latest data from the source. If they cannot connect, or periodically have trouble connecting, replication may fall behind (i.e. the replica may not have the latest data that was written to the source).
Replica Has Stopped Replicating	If neither the replica I/O thread nor the replica SQL threads are running, it means the replica is not getting the latest statements from the source and it is not executing those statements on the replica, and thus replication has stopped entirely.
Replica I/O Thread Not Running	The replica I/O thread is the thread that retrieves statements from the source's binary log and records them into the replica's relay log. If this thread isn't running, it means the replica is not able to retrieve the latest data from the source.
Replica Relay Log Space	When a replica receives updates from its source, the I/O thread stores the data in local files known as relay logs. The replica'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.
Replica SQL Thread Not Running	The replica SQL thread is the thread that reads statements from the replica's relay log and executes them to bring the replica in sync with the source. If this thread isn't running, it means the replica is not able to apply the latest changes it has read from the source, and results of queries directed to the replica may not reflect the latest changes made on the source.
Replica Seconds Behind Source	If a replica is too far behind the source, results of queries directed to the replica may not reflect the latest changes made on the source.
Replica Waiting To Free Relay Log Space	For replicas 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 source 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 replica will fall behind the source.