06 Nov, 2009
New Relic: “Mongrel count” vs “Instance count”
New Relic is the best way to track a Rails app’s performance, no question, but it still confounds me at times. Here’s something I learned today.
New Relic reports the number of instances per host; until today, I was reading this as the size of our mongrel pool.
It’s not, actually—it’s more like the ideal size of the mongrel pool. New Relic is actually counting individual instantiations of mongrels, which is to say the number of mongrels which have run. If you’ve got a pool of 8 mongrels (who could ask for more?), and 2 of them have restarted, then New Relic is going to report that you had “10 instances”.
It makes perfect sense in retrospect, but I didn’t realize this until Justin at New Relic pointed it out to me. They’re very responsive at their support site.
I haven’t had the opportunity to see how New Relic displays instance counts for Phusion Passenger deployments; if you have anything to add, please post in the comments!
