Logging and Profiling MongoDB Performance Tuning Part 3

In this blog , I am going to discuss about logging and profiling of mongodb. Logging

MongoDB log slow queries in text file which take more than 100ms . How we can access it first stop the services of mongodb .

Now in your terminal execute the following statement

sudo mongod ­dbpath /var/lib/mongodb   /* /var/lib/mongodb is path of mongodb on my system */

The above line will start the service of mongodb . Now open another terminal and start the mongodb shell using command “mongo” . you will execute your queries here and you will find those queries which take more than 100s listing on first terminal .

Profilier ­ It writes, entries document to system.profile for any query that takes time longer than specified period of time It has three level

level 0 ­ this is default level and profiler is off.

level 1 ­ this is level used to logged when query takes more than specified period of time.

level 2 ­ you will logged the all queries . It can be used for purpose to see database traffic on your system.

Below is the command which will logged those queries which take time more than 2ms.

mongod ­dbpath /var/lib/mongodb ­­profile 1 ­­slowms 2

Above command is used similar to what we have explained in logging but it will used for logging those queries which will take more than specified period of time , in my case it is 2ms.

command to find all the queries which take more time

db.system.profile.find();

It will give details of all the slow queries . It is capped collection , fixed size collection so it recycle space to store the recent query details only if there is no space left .

some queries that is really useful and we can performed on system.profile

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

It will return all those queries details which took more than 1 milli seconds, sorted by timestamp

db.system.profile.find({ns:’/school/student’}).sort({ts:1})

The above query will return all the entries in system.profile which is performed on student collection of school database sorted by timestamp.

MongoTop

mongotop 3

This command will run at every three second and give high level view of mongodb where it is utilizing it maximum time . It give list of 5 collections where the mongodb is utilizing is maximum time sorted by time utilizing in descending order along with red and write time . It will help us to figure it which collections need indexing and with the help of logger and profiling we can determine the fields which we can use for indexing .

Mongostat

mongostat ­

this command give the system level information about the mongodb . query executing per second , insert etc .The one field idx_miss% it is important for us , it is used to know when a query is executing having index on the field where the index is used or not. This is all for mongodb performance tuning .

I hope it will help you .

Thanks