- heavy mixed workload
- Ubuntu 14.04.1 LTS, 3.13.0-32-generic
- VMware, 6 cores
5-second pause in db ops was seen following this message in syslog:
- For a second or so from A to B no samples were reported by the external monitoring processes (a mongo shell process calling serverStatus and a python process monitoring system stats.)
- An extremely high context switch rate was reported at A.
- At B the monitoring processes resumed.
- At around B (to within syslog resolution of 1 second) the above message appeared in syslog.
- Starting at B for about 5 seconds db op rate dropped to 0
- However not all activity was blocked: evictions appeared to be continuing, serverStatus was being processed.
- "slots selected for switching that were unavailable" was high from B to C.
It appears that some behavior involving extreme CPU utilization at high priority from A to B, possibly involving context switches, caused the kernel to suspend those threads for 5 seconds. The threads involved with eviction apparently weren't suspended.