The concept of indexing in Apache Cassandra

Indexing in Apache Cassandra is a way to improve the efficiency and performance of queries on non-primary key columns. In Cassandra, data is organized in tables and each table has a primary key, which consists of one or more columns that uniquely identify each row in the table. Queries that use the primary key to retrieve data are very efficient, but queries that use other columns in the WHERE clause can be slower.

Cassandra has secondary indexes that enable querying on columns other than the main key columns to solve this problem. A secondary index is built on a table's column, and it maintains a different index data structure that associates the values of the indexed column with the associated table rows. Searching up the rows in the index and then obtaining the relevant data from the table, enables queries on that column to be processed quickly.

In Cassandra, secondary indexes come in two flavors: SASI (SSTable Attached Secondary Index) and traditional secondary indexes. The ability to index on numerous columns, do substring searches, and allow range queries are all capabilities of SASI indexes, which are more potent than conventional secondary indexes. They are more difficult to utilize and take up more disc space than typical secondary indexes.

When Should an Index Be Used?

• The best option for a table with several rows that include the indexed item is to use built-in indexes.

• Indexing can be used if a given column has plenty of unique values.

• Indexing can be used if a table has extra overhead for a number of reasons, such as a column with more entries.

• To query and maintain the index, we may use indexing, which is always a wise choice in these situations.

Index Creation Syntax

CREATE INDEX IF NOT EXISTS ON TABLE NAME(column_name);

Example

Let’s create a table called users with the columns "user_id," "user_name," and "user_email".

CREATE TABLE users ( 
    user_id int,
    user_name text,
    user_email text
);

Output Table

user_id

user_name

user_email

You would use the following command to establish an index on the "user_email" column −

CREATE INDEX email_index ON users (user_email);

This creates an index called "email_index" on the "user_email" column in the "users" table.

Input

The input is a CQL command that creates a secondary index named email_index on the user_email column of the user's table.

Output

The output is a message indicating whether the index was created successfully. If the index was created successfully, we can use it to retrieve data faster based on the values in the user_email column.

You can also create indexes on multiple columns by separating them with commas −

CREATE INDEX name_email_index ON users (user_name, user_email);

This creates an index called "name_email_index" on the "user_name" and "user_email" columns in the "users" table.

Input

The input is a CQL command that creates a secondary index named name_email_index on the user_email and user_name columns of the user's table.

Output

The output is a message indicating whether the index was created successfully. If the index was created successfully, we can use it to retrieve data faster based on the values in the user_email and user_user_name columns.

Conclusion

It's important to note that secondary indexes in Cassandra should be used judiciously and only on columns that are frequently queried. Overuse of secondary indexes can lead to performance issues and increased storage requirements. In general, it's better to design the data model in a way that minimizes the need for secondary indexes by using composite primary keys and denormalization.