MongoDB logging all queries

You can log all queries:

$ mongo MongoDB shell version: 2.4.9 connecting to: test > use myDb switched to db myDb > db.getProfilingLevel() 0 > db.setProfilingLevel(2) { "was" : 0, "slowms" : 1, "ok" : 1 } > db.getProfilingLevel() 2 > db.system.profile.find().pretty() 

Source: http://docs.mongodb.org/manual/reference/method/db.setProfilingLevel/

db.setProfilingLevel(2) means "log all operations".

I ended up solving this by starting mongod like this (hammered and ugly, yeah... but works for development environment):

mongod --profile=1 --slowms=1 & 

This enables profiling and sets the threshold for "slow queries" as 1ms, causing all queries to be logged as "slow queries" to the file:

/var/log/mongodb/mongodb.log 

Now I get continuous log outputs using the command:

tail -f /var/log/mongodb/mongodb.log 

An example log:

Mon Mar  4 15:02:55 [conn1] query dendro.quads query: { graph: "u:http://example.org/people" } ntoreturn:0 ntoskip:0 nscanned:6 keyUpdates:0 locks(micros) r:73163 nreturned:6 reslen:9884 88ms 

Because its google first answer ...
For version 3

$ mongo MongoDB shell version: 3.0.2 connecting to: test > use myDb switched to db > db.setLogLevel(1) 

http://docs.mongodb.org/manual/reference/method/db.setLogLevel/

MongoDB has a sophisticated feature of profiling. The logging happens in system.profile collection. The logs can be seen from:

db.system.profile.find() 

There are 3 logging levels (source):

• Level 0 - the profiler is off, does not collect any data. mongod always writes operations longer than the slowOpThresholdMs threshold to its log. This is the default profiler level.
• Level 1 - collects profiling data for slow operations only. By default slow operations are those slower than 100 milliseconds. You can modify the threshold for “slow” operations with the slowOpThresholdMs runtime option or the setParameter command. See the Specify the Threshold for Slow Operations section for more information.
• Level 2 - collects profiling data for all database operations.

To see what profiling level the database is running in, use

db.getProfilingLevel() 

and to see the status

db.getProfilingStatus() 

To change the profiling status, use the command

db.setProfilingLevel(level, milliseconds) 

Where level refers to the profiling level and milliseconds is the ms of which duration the queries needs to be logged. To turn off the logging, use

db.setProfilingLevel(0) 

The query to look in the system profile collection for all queries that took longer than one second, ordered by timestamp descending will be

db.system.profile.find( { millis : { $gt:1000 } } ).sort( { ts : -1 } ) 

I made a command line tool to activate the profiler activity and see the logs in a "tail"able way --> "mongotail":

$ mongotail MYDATABASE 2015-02-24 19:17:01.194 QUERY  [Company] : {"_id": ObjectId("548b164144ae122dc430376b")}. 1 returned. 2015-02-24 19:17:01.195 QUERY  [User] : {"_id": ObjectId("549048806b5d3db78cf6f654")}. 1 returned. 2015-02-24 19:17:01.196 UPDATE [Activation] : {"_id": "AB524"}, {"_id": "AB524", "code": "f2cbad0c"}. 1 updated. 2015-02-24 19:17:10.729 COUNT  [User] : {"active": {"$exists": true}, "firstName": {"$regex": "mac"}} ... 

But the more interesting feature (also like tail) is to see the changes in "real time" with the -f option, and occasionally filter the result with grep to find a particular operation.

See documentation and installation instructions in: https://github.com/mrsarm/mongotail