Nosql database interview questions

 

NoSQL, standing for “not only SQL,” refers to databases that store and manage data differently than relational databases. NoSQL databases are designed to handle unstructured data and are known for their flexibility. They can be categorized into four main types: document, key-value, wide-column, and graph databases.

Key Features:

Unstructured Data: NoSQL is suitable for unstructured or semi-structured data.

Scalability: These databases offer horizontal scalability.

Schema-less: NoSQL databases do not require a fixed schema.

Database transactions imply ACID properties, where “I” stands for isolation and concurrency control.  ( Used to control deadlock ) 

The (serializable) isolation property ensures that the result of concurrently executed transactions is the same as if they had been executed in some serial order.

Many DBMSs provide weaker isolation levels for performance reasons, leaving it up to the application developer to choose the proper one. Moreover, a weaker isolation level is often the default in monolithic databases, e.g., “read committed” in PostgreSQL and MySQL. Meanwhile, stronger defaults prevail in distributed databases: “repeatable read” in YugabyteDB and TiDB and “serializable” in CockroachDB and [YDB]YDB.

Difference between Relational database and NoSQL

Relational Database	NoSQL
It is used to handle data coming in low velocity.	It is used to handle data coming in high velocity.
It gives only read scalability.	It gives both read and write scalability.
It manages structured data.	It manages all type of data.
Data arrives from one or few locations.	Data arrives from many locations.
It supports complex transactions.	It supports simple transactions.
It has single point of failure.	No single point of failure.
It handles data in less volume.	It handles data in high volume.
Transactions written in one location.	Transactions written in many locations.
support ACID properties compliance	doesn’t support ACID properties
It’s difficult to make changes in database once it is defined	Enables easy and frequent changes to database
Schema  is mandatory to store the data	Schema design is not required
Deployed in vertical fashion.	Deployed in Horizontal fashion.

MongoDb

Mongodb atlas is cloud service provided by AWS 

Notes : 

1) Collections .  

     Collections are like tables in Mongodb .  

    Capped collections in MongoDB are fixed-size, high-performance collections that operate like circular buffers. They automatically overwrite the oldest documents with new data once the allocated size is filled. They maintain strict insertion order, allowing fast, sequential writes and supporting tailable cursors for real-time data streaming

Commands : 

1) mongo - to check details of installed software 

    mongod --auth 

   mongo -- help  -- mongodb connecion utility .  mongo --host ipadd -- port portnumber

    

2) ps -ef  |  grep mongod  -- to check if mongodb process is running 

   netstat -ntpl 

3) systemctl start mongod  -- to start mongodb  ( with root ) 

4)  systemctl sttaus mongod

5)  systemctl enable mongod  - enable auto start 

6) mongod  --> db.version() , show dbs ,

7) crude operation --Dml 

db.collection.insertOne()  , db.movies.insertone({"tittle":"Godzilla"})

 

8) enable auditing 

mongod --dbpath/data/db--auditDestinationfile --auditFormatBSON --auditPathdata/db/auditLog.bson

Files : 

1) /etc/mongod.conf   -- authorization : enabled 

2) /var/log/mongodb/mongod.log  

3)  

Database creation : 

1) show dbs 

2) use db_name

3) db.createcollection("movienames") 

4) show collections 

5) use db_name -->  db.dropDatabase()

6) 

Backup and Recovery Utilities

•mongoexport

•Mongoimport

•mongodump

•mongorestore

Editions of MongoDB

•MongoDBCommunity Edition ( Free for Production use)

•MongoDBEnterprise Advanced Server ( Paid License)

•MongoDBAtlas ( For Cloud)

•MongoDBRealm for mobile applications

•Upgrading from community edition to enterprise Edition possible

Difference Between Community and Enterprise Edition

•MongoDBEnterprise provides various features not available in the MongoDBCommunity edition, such as:

•In-Memory Storage Engine

•Auditing

•Kerberos Authentication

•LDAP Proxy Authentication and LDAP Authorization

•Encryption at Rest

MongoDB deployment Models

•Standalone

•Standalone installation is a single-machine installation and is meant mainly for development or experimental purposes.

•Replica set

•A replica set in MongoDBis a group of processes or servers that work together to provide data redundancy and high availability. It requires at least three servers in a cluster. These servers are configured as the primary, secondaries, or arbiters.

•Sharded

•Shardeddeployments allow you to store the data in a distributed way. A shard contains a subset of the data, and each shard must use a replica set to provide redundancy of the data that it holds. Multiple shards working together provide a distributed and replicated dataset.

This beta is designed for learners who’ve completed all the following MongoDB Skill Badges:

CRUD Operations in MongoDB

MongoDB Indexing Design Fundamentals

Optimizing and Maintaining MongoDB Cluster Reliability

Data Resilience in MongoDB Self-Managed Deployments

MongoDB Sharding Strategies

MongoDB Aggregation Fundamentals

MongoDB Query Optimization Techniques

Monitoring MongoDB with Built-in Tools

Securing MongoDB Self-Managed: Authentication & Authorization

MongoDB Overview: Core Concepts and Architecture

Optimizing MongoDB Performance with Tuning Tools

Securing MongoDB Self-Managed Networking

MongoDB Encryption at Rest with BYOK

References :

https://blog.ydb.tech/do-we-fear-the-serializable-isolation-level-more-than-we-fear-subtle-bugs-5a025401b609