Monitoring MySQL’s replication has always been a bit hit and miss, especially when trying to detect whether a slave is becoming overloaded or not. There’s been a few ways to do this in the past:

• Monitor the Seconds_behind_master variable from SHOW SLAVE STATUS, which is the difference between the timestamp passed down from the master that the event was executed, to the time that the SQL thread started executing the event.
• Use something like mk-heartbeat, which operates in the same way as Seconds_Behind_Master (trying to show you the actual time difference between the master and slave),

I’ve written before about how you can monitor the last wait per connection with Performance Schema in MySQL 5.5.

That solution joined the performance_schema.events_waits_current with the performance_schema.threads and INFORMATION_SCHEMA.PROCESSLIST tables.

Joining to INFORMATION_SCHEMA.PROCESSLIST is a necessary evil

I love our community.

Not long after posting my update on ps_helper, I had a couple of comments around the formatting of values within the output. Daniël van Eeden gave the suggestion that I could add a couple of Stored Functions, for formatting byte and time based values.

Of course, this was a great idea – not least for myself, because I no longer have to worry about how to format certain columns in the output.

I’ve added the following:

format_bytes()
format_time()