quoting http://askmonty.org/worklog/?tid=177

I want to log all or a sample of errors on the server side into a new log file
(not general, error or slow query log) and into a file that can be rotated. In the
facebook patch I added code to sample query errors into the slow query log using -
-log-sample-error-rate:

• when 0 do not sample
• when 1 then log all errors
• when > 1 then sample 1 of --log-sample-error-rate queries

This should have:

• query text
• username
• timestamp
• database
• errno
• error text
• client IP

The log should support rotation and possibly auto-rotation when it reaches a
certain size.