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MongoDB Interview Questions


1) What do you understand by NoSQL databases? Is MongoDB a NoSQL database? explain.

At the present time, the internet is loaded with big data, big users, big complexity etc. and also becoming more complex day by day. NoSQL is answer of all these problems, It is not a traditional database management system, not even a relational database management system (RDBMS). NoSQL stands for “Not Only SQL”. NoSQL is a type of database that can handle and sort all type of unstructured, messy and complicated data. It is just a new way to think about the database.

Yes. MongoDB is a NoSQL database.


2) What are the different types of NoSQL databases? Give some example.

NoSQL database can be classified as 4 basic types:

  1. Key value store NoSQL database
  2. Document store NoSQL database
  3. Column store NoSQL database
  4. Graph base NoSQL databse

There are many NoSQL databases. MongoDB, Cassandra, CouchBD, Hypertable, Redis, Riak, Neo4j, HBASE, Couchbase, MemcacheDB, Voldemort, RevenDB etc. are the examples of NoSQL databases.


3) What type of DBMS is MongoDB?

MongoDB is a document oriented DBMS>


4) What is the difference between MongoDB and MySQL?

Although MongoDB and MySQL both are free and open source databases, there is a lot of difference between them in the term of data representation, relationship, transaction, querying data, schema design and definition, performance speed, normalization and many more. To compare MySQL with MongoDB is like a comparison between Relational and Non-relational databases.


5) Why MongoDB is known as best NoSQL database?

MongoDb is the best NoSQL database because, it is:

Document Oriented

Rich Query language

High Performance

Highly Available

Easily Scalable


6) What is the difference b/w MongoDB and CouchDB?

MongoDB and CouchDB both are the great example of open source NoSQL database. both are document oriented databases. Although both stores data but there is a lot of difference between them in terms of implementation of their data models, interfaces, object storage and replication methods etc.


7) What is a Namespace in MongoDB?

Namespace is a concatenation of the database name and the collection name. Collection, in which MongoDB stores BSON objects.


8) Can journaling features be used to perform safe hot backups?

Yes.


9) Why does Profiler use in MongoDB?

MongoDB uses a database profiler to perform characteristics of each operation against the database. You can use a profiler to find queries and write operations


10) If you remove an object attribute, is it deleted from the database?

Yes, it be. Remove the attribute and then re-save() the object.


11) In which language MongoDB is written?

MongoDB is written and implemented in C++.


12) Does MongoDB need a lot space of Random Access Memory (RAM)?

No. MongoDB can be run on small free space of RAM.


13) What language you can use with MongoDB?

MongoDB client drivers supports all the popular programming languages so there is no issue of language, you can use any language that you want.


14) Does MongoDB database have tables for storing records?

No. Instead of tables, MongoDB uses “Collections” to store data.


15) Do the MongoDB databases have schema?

Yes. MongoDB databases have dynamic schema. There is no need to define the structure to create collections.


16) What is the method to configure the cache size in MongoDB?

MongoDB’s cache is not configurable. Actually MongoDb uses all the free spaces on the system automatically by way of memory mapped files.


17) How to do Transaction/locking in MongoDB?

MongoDB doesn’t use traditional locking or complex transaction with Rollback. MongoDB is designed to be light weighted, fast and predictable to its performance. It keeps transaction support simple to enhance performance.


18) Why 32 bit version of MongoDB are not preferred ?

Because MongoDB uses memory mapped files so when you run a 32-bit build of MongoDB, the total storage size of server is 2 GB. But when you run a 64-bit build of MongoDB, this provides virtually unlimited storage size. So 64-bit is preferred over 32-bit.


19) Is it possible to remove old files in the moveChunk directory?

Yes, These files can be deleted once the operations are done because these files are made as backups during normal shard balancing operation. This is a manual cleanup process and necessary to free up space.


20) What will have to do if a shard is down or slow and you do a query?

If a shard is down and you even do query then your query will be returned with an error unless you set a partial query option. But if a shard is slow them Mongos will wait for them till response.

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