To achieve high availability and scalability, the term "eventual consistency" refers to having copies of data on several machines. As a result, any changes made to a data item on one system must be replicated on all other replicas.

Data replication may not be instantaneous since some copies will be updated right once while others will take longer. These copies may be inconsistent at first, but with time, they become consistent. As a result, the term "ultimate consistency" was coined.

BASE: Basically Available, Soft state, Eventual consistency

• Basically Available, means according to the CAP theorem, DB is always available.
• Soft State, means even if there is no input, the status of the system can change.
• Eventual Consistency, means Over time, the system will grow more consistent.

Advantages Of NoSQL Database:

• It is possible to use it as a primary or analytic data source.
• Capacity for Big Data.
• There isn't a single point of failure.
• Replication is simple.
• There is no requirement for a separate caching layer.
• It offers quick performance as well as horizontal scalability.
• Can effectively handle structured, semi-structured, and unstructured data.
• Object-oriented programming is a type of programming that is simple to use and adaptable.
• A dedicated high-performance server isn't required for NoSQL databases.
• Key Developer Languages and Platforms are supported.
• RDBMS is more difficult to implement.
• It has the potential to be the key data source for web-based applications.
• Manages large data, including the velocity, diversity, volume, and complexity of data.
• Distributed database and multi-data centre operations are two areas where he shines.
• Removes the need for a dedicated cache layer for data storage.
• Provides a flexible schema that may be readily changed without causing downtime or service disruption.

Disadvantages of NoSQL Database:

• There are no norms for standardisation.
• Querying capabilities are limited.
• Databases and tools for Relational Database Management Systems (RDBMS) are relatively established.
• It lacks standard database features such as consistency when several transactions are carried out at the same time.
• As the volume of data grows, it becomes more difficult to preserve unique values as keys become more difficult to remember.
• With relational data, it doesn't work as well.
• For novice developers, the learning curve is steep.
• For businesses, open-source choices are less common.

Here we will see some important questions in NoSQL:

What is NoSQL?

NoSQL refers to a group of database technologies developed in response to an increase in the amount of data held about persons, things, and products. The number of times this data is accessed, as well as the performance and processing requirements. Relational databases, on the other hand, were not created to handle the scale and agility difficulties that modern applications confront, nor were they built to take use of today's low-cost storage and processing power.

Why is NoSQL Eventual Consistency?

The reason for this is because almost all NoSQL systems are built to be distributed, and maintaining strict consistency in fully distributed systems has a super-linear overhead (meaning you can only scale so far before things slow down, and when they do, you need to scale again).

What is CAP Theorem?

Consistency, Availability, and Partition Tolerance (CAP) Theorem for Databases The CAP theorem is a theoretical computer science hypothesis about distributed data stores that states that in the event of a network failure on a distributed database, either consistency or availability can be provided, but not both.

Does CAP Theorem Apply to NoSQL?

According to the CAP theorem, the NoSQL database has restrictions. Only two of a database's three promises — consistency, availability, and partition tolerance — can be met. The CAP theorem is used in a distributed system when only two of the three desirable qualities are provided.

How does NoSQL DB budget memory?

The Replication Node is the major memory consumer and handles the data in a NoSQL DB store. The size of the Java heap and cache used by the Replication Node can affect performance. By default, NoSQL DB calculates the Replication Node heap and cache based on the amount of memory available to the Storage Node.

We propose using the -memory mb flag for makebootconfig or the memory mb Storage Node parameter to provide the available memory for a Storage Node. If you don't specify memory mb, the memory available on the node will be used. The heap for the Replication Node processes hosted by that Storage Node will then be 85 percent of memory mb. If the Storage Node has multiple Replication Nodes, the memory will be shared evenly among them.

The per-RN memory will be dynamically computed if the number of Replication Nodes on a Storage Node varies. The rnHeapPercent Storage Node option controls the heap proportion used. You have the option of changing the default value of 85 percent. Each Replication Node has a cache, and the cache size is set to 70% of the Replication Node heap by default. The rnCachePercent Replication Node parameter can be used to override the default of 70%.

The heap of the Replication Node can also be determined directly by specifying the -Xmx parameter in the javaMiscParams parameter of the Replication Node. Similarly, the cache Size Replication Node parameter can be used to set the size of the Replication Node cache. While this is feasible, it is recommended that you utilise the Storage Node memory mb setting instead.

As an example, imagine you set memory mb to 3000 to allow a Storage Node to use 3000 MB of memory. The heap for each RN will be (3000 *.85)/2 = 1275MB if the Storage Node hosts two Replication Nodes. Each RN cache will be 892MB (1275 *.70).

Does NoSQL Database Interact With Oracle Database?

Oracle Database External Table capabilities are supported by NoSQL Database for fetching records. This allows you to run some Oracle Database queries and get records from a NoSQL database.