> I was watching a Memcached video spoken by John Adams when I heard > something that made me curious. When one gets stats from memcached, > does it really perform a global lock? Does anyone have any good test > cases on what sort of impact there is with an increasing node size > with respect to performance degradation?
'stats sizes' grabs a global lock and iterates the whole cache. we don't recommend you run that one. All other stats commands are extremely fast. > I am looking to do some research on expanding our product to support > real-time monitoring, management, and analysis of memcached. But I'm a > little concerned that this lock occurs during every stat collection, > so much to the point that John Adams mentions that it can noticeably > degrade the performance of memcached. I tried to do some research on > my own but am finding very little performance analysis or any > benchmark info with respect to constant polling (minimally 30 sec > interval) of a enterprise-level memcached distributed system. Has > anyone seen bad performance with respect to a large cluster and > gathering stats? Any info would be great, thanks! There is no major lock every stat collection. There's a minor lock and reading the values is very fast. A while ago twitter was running an extremely old version of memcached and they took a long time to upgrade. That particular version had a bug in stats collection that was *missing* a mutex lock, and would thus crash sometimes. So they were afraid of running stats commands. That bug hasn't existed for three years at least. -Dormando
