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Configuring profiling in MongoDB

For MongoDB to work correctly with QAN (Query Analytics), you need to enable profiling in your mongod configuration. When started without profiling enabled, QAN displays the following warning:


The warning message displayed when profiling is not enabled

It is required that profiling of monitored MongoDB databases be enabled.

Note that profiling is not enabled by default because it may reduce the performance of your MongoDB server.

Enabling Profiling on Command Line

You can enable profiling from command line when you start the mongod server. This command is useful if you start mongod manually.

$ sudo mongod --dbpath=DATABASEDIR --profile 1 --slowms 200 --rateLimit 100

Note that you need to specify a path to an existing directory that stores database files with the dbpath. When the profile option is set to 1, mongod only collects the profiling data for slow operations. The slowms option sets the minimum time for a slow operation. In the given example, any operation which takes longer than 200 milliseconds is a slow operation.

The rateLimit option refers to the number of queries that the MongoDB profiler collects. The lower the rate limit, the less impact on the performance. However, the accuracy of the collected information decreases as well.

Enabling Profiling in the Configuration File

If you run mongod as a service, you need to use the configuration file which is found by default as follows:


In this file, you need to locate the #operationProfiling: section and add the following settings:

   slowOpThresholdMs: 200
   mode: slowOp
   rateLimit: 100

These settings affect mongod in the same way as the command line options described in section Enabling Profiling on Command Line. Note that the configuration file is in the YAML format. In this format the indentation of your lines is important as it defines levels of nesting.

Restart the mongod service to enable the settings.

$ sudo service mongod restart

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