The client stats table has an "empty queries" column. What does that mean? Simple googling just tells me "The number of times this client's connections sent empty queries to the server." /facepalm
Unfortunately this is not documented in the MySQL manual - the page would be this one. I didn't know the answer, but I did manage to debug it from the 5.5 source:
It is queries to the server that do not produce SQL queries. i.e.
(You need to add --comments, because the command line utility by default will strip them.)
How to debug something like this in MySQL:
As Rolando points out, the CLIENT_STATISTICS table is not a MySQL table.
However, I'm fairly sure it would be mapped to the 'Com_empty_query' status variable:
But I cannot seem to trigger this counter at all.
At first I thought just issuing a
Or a query that returned an empty result set:
But none of those are triggering it. I delved into the source code, but it wasn't very helpful in my 10 minutes of looking, and the only thing I can see is that it would indicate an issue with client buffers sending commands.