MySQL Bugs: #57847: Replication heartbeat documentation needs to be improved

Bug #57847	Replication heartbeat documentation needs to be improved
Submitted:	29 Oct 2010 15:20	Modified:	17 Jan 2018 10:46
Reporter:	Lenz Grimmer	Email Updates:
Status:	Closed	Impact on me:	None
Category:	MySQL Server: Documentation	Severity:	S3 (Non-critical)
Version:	5.5	OS:	Any
Assigned to:		CPU Architecture:	Any
Tags:	Administration, documentation, heartbeat, replication

Description:
The "Checking Replication Status" section of the 5.5 reference manual does not yet cover the newly introduced "Replication Heartbeat" feature (WL#342, BUG#20435, BUG#29309) that is described here: http://dev.mysql.com/tech-resources/articles/introduction-to-mysql-55.html 

(See BUG#54763 for a related request)

How to repeat:
Try to find any information about "Replication Heartbeat" in the MySQL 5.5. reference manual. Observe that only the related variables and configuration options are described, but not the overall functionality/usability.

http://dev.mysql.com/doc/refman/5.5/en/change-master-to.html
http://dev.mysql.com/doc/refman/5.5/en/replication-options-table.html

Suggested fix:
Add a paragraph to the "Checking Replication Status" chapter that explains how to use the MASTER_HEARTBEAT_PERIOD option and the Slave_heartbeat_period and Slave_received_heartbeats variables

Alternatively, create a separate chapter that better explains the usage of this new 5.5 feature.

Posted by developer:
 
I'm clearing up old bugs - thanks for your report. Sorry this wasn't handled before. This topic has been overlooked for a number of releases. I have updated the 5.7 and 8.0 topics with information about the move of these status variables to the Performance Schema replication tables, and put the following paragraph in 5.5 and 5.6:

 The SHOW STATUS statement also provides some information relating specifically to replication slaves. The replication heartbeat information displayed by SHOW STATUS lets you check that the replication connection is active even if the master has not sent events to the slave recently. The master sends a heartbeat signal to a slave if there are no updates to, and no unsent events in, the binary log for a longer period than the heartbeat interval. The MASTER_HEARTBEAT_PERIOD setting on the master (set by the CHANGE MASTER TO statement) specifies the frequency of the heartbeat, which defaults to half of the connection timeout interval for the slave (slave_net_timeout). The Slave_last_heartbeat variable for SHOW STATUS shows when the replication slave last received a heartbeat signal. 

Updates should show in https://dev.mysql.com/doc/refman/8.0/en/replication-administration-status.html and earlier versions within a day or two.