why did serverstatus have a bad effect on mongod write operation?

Question

I have 1 mongos, 3 mongod and 3 config server. when I write some documents, sometimes the insert speed of one of mongods is very slow and there're "serverstatus was very slow" in mongod log file. why?

the version is 2.0.4

Answer 1

That message actually reflects the fact that your server was slow, not that serverStatus is causing the problem. If the serverStatus command (which is run periodically by MMS agents for example) is slow, it will log that warning - it is a symptom rather than a cause.

It is quite lightweight as a command, so if it is returning slowly enough to warn you about it then the host is likely very busy at that time.

The usual places to look for load apply (high inserts/updates, table scans, poorly indexed queries, disk issues, RAM/CPU contention, page faults etc.).