We recently started graphing the innodb_row_lock_time status variable in our monitoring system.
I noticed something I can't understand on a graph for a busy server:
Between 04:55PM and 04:57PM, the value of this counter changed from 488,101,000 to 488,504,000. The MySQL documentation says:
innodb_row_lock_time The total time spent in acquiring row locks, in milliseconds.
How is it possible that during those 2 minutes, the server spent 403,000 ms in acquiring row locks? 2 minutes is only 120,000 ms
The only explanation that comes to mind is that this value is a sum of all threads but I cannot find any documentation to confirm this theory.
The server is MySQL 5.1