MySQL innodb_row_lock_time is more than wall clock time

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