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Is NoSQL DBMS a Replacement for Relational Database Management System?

March 2, 2022

NoSQL is a non-relational database that has become a preferred option for modern applications. Its changing data sets fit into a flexible data model. Developers find its agile features enticing because they facilitate quick application updates.

Relational databases have been a trusted DMS for a while now. Their maturity and long existence make them the go-to option for several organizations. Yet, as technology advances and companies continue handling big data, SQL-based relational database limitations are becoming apparent. Organizations are considering NoSQL databases on use cases that RDBMS are inapplicable.

This article will discuss the features of NoSQL DBMS and how they compare with SQL-based relational databases. It also explains the CAP theorem and when to choose either NoSQL DBMS or an RDBMS.


A relational database management system relies on structured query language. No-SQL database, however, does not use SQL. Being a non-SQL database, NoSQL stores data in a semi-structured or unstructured format. That is not the case for RDBMS that must keep data in a structured format to remain compatible with SQL.

An RDMS provides data in columns and rows in a properly structured format. Data stored in tables has an identifier called the primary key. This identifier helps link the different database tables to enhance quick data retrieval.

However, this is not the case with a NoSQL database, as it uses other means other than the primary key. A SQL-based database is a relational database; NoSQL takes the name distributed database. As a distributed database, NoSQL has no connection with any databases.

There are other differences between RDBMS and NoSQL databases.

These are minor, but they include:

  • Scalability: a relational database management system is scalable vertically while NoSQL is scalable horizontally. In vertical scalability, an organization must improve the performance of its database by increasing the capacity of a single database. In horizontal scalability, an organization can increase server power by increasing the number of servers available.
  • Schema: a relational database has a fixed schema. Inserted data takes a proper format to allow the primary and foreign keys to align data in the table. But in NoSQL, inserted data takes any form; thus, it does not require a schema. No-SQL is quite flexible. One can insert data at any time and make updates without prior notice.
  • Stored procedures: a relational database contains stored procedures required to understand the data. These procedures help users track the patterns that data follows in a computer system. NoSQL lacks similar procedures, making it challenging to understand data on these databases.

The CAP theorem and NoSQL DBMS

It is crucial to understand NoSQL’s limitations. This database cannot maintain consistency and high availability at the same time. According to Eric Brewer’s CAP theorem, one can only achieve two out of three database guarantees. The three guarantees include consistency, partition tolerance, and availability.

Consistency refers to when all nodes within a network can access the same data concurrently. Availability means every request receives a response on whether it went through or failed. Partition guarantees that the database will keep working as usual even after a complete failure of the system. Of the three database guarantees, the CAP theorem notes that any database can only offer two of them at most. Partitioning is often a requirement in a NoSQL system; the tradeoff becomes either consistency or availability.

The CAP theorem initiated the development of classification for NoSQL databases. The classification identifies NoSQL databases based on the type of characteristics they support.

  • CA database: this is a NoSQL database that offers consistency and availability across all nodes in a network. But this means the NoSQL database must sacrifice the partitioning between the nodes.
  • CP database: this NoSQL database delivers consistency and partition tolerance. The tradeoff is availability. Upon partitioning, the system shuts down the non-consistent node, making it unavailable at that time.
  • AP database: this NoSQL delivers availability and is partition tolerant. The system compromises on the three guarantees of a database to omit consistency.

Can NoSQL replace RDMS?

For a long time, companies primarily relied on RDBMS to handle data. But in today’s era of big data, organizations are beginning to reconsider their continued use of SQL-based databases. NoSQL is now an enticing option. Should organizations dump RDBMS for NoSQL?

Well, that might be an appropriate option in some cases. However, while making this choice, it is significant to understand that NoSQL is not a replacement for RDBMS; it is a complementary option. It helps ‘fill’ the gaps that relational databases leave when dealing with big data. Both relational and non-relational databases have critical functions that companies cannot ignore. So, they cannot entirely omit one database system by choosing another.

When to choose NoSQL DBMS

NoSQL DBMS is applicable when you’re looking for:


Using NoSQL databases is crucial during scaling. Both SQL and NoSQL databases are scalable. But NoSQL has a higher capability for scaling because it relies on horizontal scaling. With NoSQL, you can add as many servers as possible to improve the capacity of the servers.

Pace of development

Organizations should choose NoSQL databases over SQL when the pace of development is a critical factor. NoSQL databases allow developers to take complete control of the data structure. That means the developer can make quick iterations and code changes to modify the data.

SQL-based databases limit this function. They limit a developer’s control over a data structure. So, during any changes, a developer must seek permission from the database administrator to implement them.

New application paradigms

Besides, NoSQL databases are enticing when dealing with new application paradigms. The high scalability of NoSQL databases adapts to modern trends. NoSQL databases have adapted to automation, making them compatible with cloud services. So, deploying databases at scale while supporting microservices is easy when using NoSQL databases.

When to choose RDBMS

RDBMS are robust when it comes to:

Data structure

Despite their limitations, relational databases remain a valuable option to many organizations. The data structure is a significant factor when using an SQL-based database. If a company is dealing with structured data and needs Atomicity, Consistency, Isolation, and Durability (ACID) compliance, an RDBMS is the best choice.

Because of their consistency and guarantee of data integrity through the ACID properties, relational databases are a good fit for complex transactions. They are common in transaction-oriented systems like CRM tools and e-commerce platforms. They offer data integrity because of their fixed schema. Although this may appear to be a limiting factor, it makes RDBMS more secure.

Data querying

Another factor that may make organizations favor this database system is data querying. If you need to query data more often, SQL databases are better than NoSQL databases. They are friendlier when conducting data queries compared to NoSQL databases. NoSQL may take extra time processing the data, which might bring cost implications.


There is a modern trend towards big data, cloud services, and a desire for faster application updates. So, organizations are taking more interest in NoSQL databases. Relational databases are becoming less desirable because of their limitations, such as a complex structure and limited scalability. NoSQL appears to be a more promising option because of its horizontal scalability and adoption of automation.

Even so, relational databases remain crucial to some organizations. They offer the most secure data forms because of their ACID compliance and data integrity guarantee. Organizations must consider this option, especially when dealing with sensitive use cases. So, banks and other financial institutions may keep using RDBMS for longer. NoSQL database management systems are unlikely to replace relational databases but rather complement them.

Further reading

Peer Review Contributions by: Collins Ayuya