Large database query taking site down


I recently activated the Dev dashboard, so that I was able to update the snapshot plugin I have installed.
However activating this brought down one of the sites on the network.

When I looked at the log, there was an one million database string in there. The error log file was increasing in size at quite an alarming rate.

Once I had disabled the Dev dashboard plugin I was able to reach the site again.

Do you know what and why this is happening?
I can supply you with a copy of the log file if need be.

Any help would be much appreciated.