Profiler collects fine grained data about MongoDB write operations, cursors, database commands on a running mongod instance.
You can enable profiling on a per-database or per-instance basis.
The profiler is off by default.
Profiler writes all the data it collects to the system.profile collection, which is a capped collection.
*.Profiling Levels
0 – the profiler is off, does not collect any data
1 – collects profiling data for slow operations only. By default slow operations are those slower than 100 milliseconds.
2 – collects profiling data for all database operations.
Enable Profiling : db.setProfilingLevel(1, { slowms: 20 })
Disable Profiling : db.setProfilingLevel(0)
Get Profiling Info: db.getProfilingStatus()
All details regarding performance issues related written in mongod.log file by default located in /var/log/messages/mongd/mongd.og
For more detail about profiling : Click Here