Basic Question: Why would there be disk fetches when there is unallocated RAM?
I have a web app with 7 c1.mediums running 20 nginx/passenger processes apiece, each of which connects to a membase cluster of 3 membase m1.small instances.
Periodically the global waiting queue spikes to 60 on every box, which typically means one of the three external depedencies my web app has - MYSQL, Membase or Redis - is blocking or stalled.
I believe membase is the cause of this global waiting queue spike I am seeing now. When I look at the membase web console, I see several graphs that I cannot explain.
So, let me start with a basic question - why would there be any disk fetches if my membase cluster is only 1/3 used (1GB in use out of 3GB total)? Shouldn't disk fetching happen only when I am at or near the 3GB limit?