Answer:

You can use the following method to generate random string into a collection in MongoDB:

function randomString() { 
        var chars = 
"0123456789ABCDEFGHIJKLMNOPQRSTUVWXTZabcdefghiklmnopqrstuvwxyz"; 
        var randomstring = ''; 
        var string_length = 100;
        for (var i=0; i<string_length; i++) { 
                var rnum = Math.floor(Math.random() * chars.length); 
                randomstring += chars.substring(rnum,rnum+1); 
        } 
        return randomstring; 
} 

for(var i=0; i<2000000; i++){db.test.save({x:i, data:randomString()});} 

Answer:

In you mongo shell, execute the following command:

var sum = 0; db.getMongo().getDBs()["databases"].forEach(function(x) { sum += db.getMongo().getDB(x.name).stats().indexSize }); print(sum)

Answer:

To see how long a MongoDB instance was running, you can login into the mongo shell, and enter

db.serverStatus().uptime / 3600

The above command reply the value in term of hours.

Answer:

The easiest way is login into the MongoDB using the shell, enter the command:

db.adminCommand({getLog: "startupWarnings" })

Answer:

Simply type the following command in your MongoDB's shell

db.version()

Answer:

To select (find) a document in MongoDB, you can use the following syntax in the mongodb Interactive shell.

use my_db
db.users.find({name:"peter"})

You need to switch to the current database (e.g. my_db) and then execute your select statement.

Answer:

Like MySQL, you can get a better understanding of the performance of your MongoDB's query, you can use the $explain feature.

E.g.

db.collection.find(query).explain();

Answer:

To repair and compact a database in MongoDB, you can use the following command in the mongodb Interactive shell.

1. Select the database

use test

2. Repair the current database

db.repairDatabase()

Done.

Answer:

In MongoDB, to count the total number of objects in the collection, you can use the following statement in the mongodb Interactive shell.

db.test.count()

The above statement will return the total number of objects in the collection "test"

Answer:

In an given collection, if you want to add an index on a specify field, you can do the following in the mongodb Interactive shell.

db.test.ensureIndex( { name : 1 } )

The key "name" from now on will have index enabled.