分析数据库操作的性能

Specify the Threshold for Slow Operations¶

The threshold for slow operations applies to the entire mongod instance. When you change the threshold, you change it for all databases on the instance.

By default the slow operation threshold is 100 milliseconds. Databases with a log level of 1 will log operations slower than 100 milliseconds.

To change the threshold, pass two parameters to the db.setProfilingLevel() helper in the mongo shell. The first parameter sets the log level for the current database, and the second sets the default slow operation threshold for the entire mongod instance.

For example, the following command sets the log level for the current database to 0, which disables profiling, and sets the slow-operation threshold for the mongod instance to 20 milliseconds. Any database on the instance with a log level of 1 will use this threshold:

db.setProfilingLevel(0,20)

Check Profiling Level¶

To view the profiling level, issue the following from the mongo shell:

db.getProfilingStatus()

The shell returns a document similar to the following:

{ "was" : 0, "slowms" : 100 }

The was field indicates the current level of profiling.

The slowms field indicates how long an operation must exist in milliseconds for an operation to pass the “slow” threshold. MongoDB will log operations that take longer than the threshold if the profiling level is 1. This document returns the profiling level in the was field. For an explanation of log levels, see Profiling Levels.

To return only the log level, use the db.getProfilingLevel() helper in the mongo as in the following:

db.getProfilingLevel()

Disable Profiling¶

To disable profiling, use the following helper in the mongo shell:

db.setProfilingLevel(0)

Enable Profiling for an Entire mongod Instance¶

For development purposes in testing environments, you can enable database profiling for an entire mongod instance. The profiling level applies to all databases provided by the mongod instance.

To enable profiling for a mongod instance, pass the following parameters to mongod at startup or within the configuration file:

mongod --profile=1 --slowms=15

This sets the profiling level to 1, which collects profiling data for slow operations only, and defines slow operations as those that last longer than 15 milliseconds.

Database Profiling and Sharding¶

You cannot enable profiling on a mongos instance. To enable profiling in a shard cluster, you must enable profiling for each mongod instance in the cluster.

Example Profiler Data Queries¶

This section displays example queries to the system.profile collection. For an explanation of the query output, see 数据库事件探查器输出.

To return the most recent 10 log entries in the system.profile collection, run a query similar to the following:

db.system.profile.find().limit(10).sort( { ts : -1 } ).pretty()

To return all operations except command operations ($cmd), run a query similar to the following:

db.system.profile.find( { op: { $ne : 'command' } } ).pretty()

To return operations for a particular collection, run a query similar to the following. This example returns operations in the mydb database’s test collection:

db.system.profile.find( { ns : 'mydb.test' } ).pretty()

To return operations slower than 5 milliseconds, run a query similar to the following:

db.system.profile.find( { millis : { $gt : 5 } } ).pretty()

To return information from a certain time range, run a query similar to the following:

db.system.profile.find(
                       {
                        ts : {
                              $gt : new ISODate("2012-12-09T03:00:00Z") ,
                              $lt : new ISODate("2012-12-09T03:40:00Z")
                             }
                       }
                      ).pretty()

The following example looks at the time range, suppresses the user field from the output to make it easier to read, and sorts the results by how long each operation took to run:

db.system.profile.find(
                       {
                         ts : {
                               $gt : new ISODate("2011-07-12T03:00:00Z") ,
                               $lt : new ISODate("2011-07-12T03:40:00Z")
                              }
                       },
                       { user : 0 }
                      ).sort( { millis : -1 } )

Show the Five Most Recent Events¶

On a database that has profiling enabled, the show profile helper in the mongo shell displays the 5 most recent operations that took at least 1 millisecond to execute. Issue show profile from the mongo shell, as follows:

show profile