Bug #69278 Docs on Seconds_behind_master might be wrong
Submitted: 19 May 2013 0:13 Modified: 18 Jun 2013 14:49
Reporter: Baron Schwartz (Basic Quality Contributor) Email Updates:
Status: Closed Impact on me:
None 
Category:MySQL Server: Documentation Severity:S3 (Non-critical)
Version: OS:Any
Assigned to: Jon Stephens CPU Architecture:Any

[19 May 2013 0:13] Baron Schwartz 
Description:
This page, http://dev.mysql.com/doc/refman/5.6/en/show-slave-status.html

Has a section that says the following:

Seconds_Behind_Master

This field is an indication of how “late” the slave is:

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.

[/snip]

Unless something has changed in the server, I do not believe this is correct. I think the field measures the difference between the server's current timestamp and the timestamp at which the currently-being-processed event was executed. If no event is currently being processed, it is 0.

How to repeat:
Check whether I'm wrong :-)
[13 Jun 2013 13:28] MySQL Verification Team 
Hello Baron,

Thank you for the feedback.

Regards,
Umesh
[18 Jun 2013 14:49] Jon Stephens 
(I think the text already says essentially the same thing as the submitter, but it was not at all well worded.)

Fixed in mysqldoc rev 35444.