Comment 4 for bug 504696

Thought about an alternative & potentially more efficient implementation:

lagmon.py as above, but stuffing the results into memcache rather than a DB table.
Appservers query memcached for lag, falling back to the replication_lag() stored procedures if memcache is down for any reason.

Problem with this approach is the appservers still need to query the database to determine what their slave node number is, which potentially could change between requests with database load balancers and config file reloading brought into the equasion.