We all are aware about the ACID Properties of Database System (Atomicity, Consistency, Isolation, Durability).
If you don’t know about the ACID, please visit below article.

ACID Properties in Database System (Atomicity, Consistency, Isolation, Durability)

In last one decade, lots of new Database Products available in the Market. The types are: RDBMS Products, NoSQL Products, BIGDATA, MPP Products.

My Question is, how do you choose best database product for your project?

Traditional Answer, The first preference of Database Designer would be ACID Properties oriented Databases.

But most of the NoSQL Databases are not providing full support of ACID Properties, then also NoSQL Databases are popular and People are using it for different purposes.

Because most of the NoSQL Databases are not ACID oriented, but they are CAP oriented.

What is CAP theorem (Consistency, Availability, Partition)?

CAP Published by Eric Brewer in 2000, the theorem is a set of basic requirements that describe any distributed system like: NoSQL Cassandra, MongoDB, CouchDB.

Consistency:

All nodes can see the same data at the same time. The data are the same across the cluster, so you can read or write any node.

Each transaction start and end in consistent stats so that all nodes can access the same data. Actually, It is achieved by update all nodes before reading.

Availability:

Here, The meaning of Availability is to access cluster in any situation like: server goes down, server delay. The system should always respond to a request, even if data is not in sync or inconsistent state, It prints the message like “This cluster data are not updated”.

Partition:

Here, the meaning of Partition is to avoid any type of system failure and system should run with available nodes or data. It does not allow any single point of failure because data replicated across all the clusters.

The Partition can work with Consistency (CP) or can work with Availability (AP) means, you can never find any Database System which follows the full CAP theorem.

Storage System with Partition and Consistency (CP):
Redis, MongoDB, AppFabric Caching, and MemcacheDB.
Storage System with Partition and Availability (AP):
Cassandra, DynamoDB, and CouchDB.

Database ACID Properties:

ACID properties are an ancient and valuable concept of database theory. I know that you can find lots of posts about this topic, but still, I would like to start my journey with this subject as one of very important and my favourite theory of Database system.

Database System plays with lots of different types of transactions where all transaction has a particular characteristic. This characteristic is known ACID Properties.

ACID Properties take grantee for all database transactions to accomplish all tasks.

Many times interviewers ask this question in an interview that, What is ACID Property in database?

Here I am going to explain with a simple example.

A = Atomicity

C = Consistency

I = Isolation

D = Durability

First,

Atomicity: means either all or none, for example,

One Application is going to insert 30 records in one transaction. During this insertion, any problem occurs, and at this point, only 12 records have processed. In this state transaction is not going to insert only 12 records it will roll back this whole transaction, so this will process either all or none.

Consistency: means to bring database from one valid state to another valid state.

There should be always defined some data rule, constraint, trigger at database end as well as application end.

Whatever data is going to insert they all should be validated by setting rules and ensure that there are no invalid data is going to insert in the database so this way it will manage consistency of the database.
In any case running transaction violate rule at that same time entire transaction will be rollback.

Isolation: means each transaction is unaware of another transaction.

One shop seller is selling items very fast, and the stock is also decreasing. At the same time, another person is also adding a new item in the stock.

Here, this both transactions is different and unaware of each other.

Isolation level ensures that one transaction is not interrupted by another transaction.

For database transaction, this one of the important properties because any database system is going with lots of concurrent and parallel transactions where Isolation property is very much required and ensure that all transactions are defined under proper isolation level.

A different database technology has different type of default Isolation level like,

Oracle has READ_COMMITTED

MySQL has REPETABLE_READ

MSSQL has READ_COMMITTED

PostgreSQL has READ_COMMITTED

DB2 has READ_COMMITTED

Read_committed Isolation level is most preferable, but many times it’s also required to show READ_UNCOMMITTED data in a data history kind of pages.

Durability: means to keep committed data forever.

Application inserted 30 records in one transaction, and this transaction is completed and committed successfully in the database that means records persist forever in the database until and unless it’s not deleted by any application users or database users.