I upgraded to Couchbase 3.0 (community edition) and am experiencing a performance drop with C SDK 2.4.2. My log shows that Couchbase is processing some requests quickly, then stops to process them for about 0.5 seconds, then processes some requests, then stops to process requests, etc.
I have special keys in the database that serve the purpose of mutexes. When a mutex cannot be locked, the currently executing fiber in the application goes to a sleep and then tries again. The problem was that the time to sleep was set too high. The fix was to make the time to sleep lower. In addition, the time to sleep is randomized now.