Composite Partition Key
Explore the concept of composite partition keys in Apache Cassandra and how they enable efficient data distribution by combining multiple columns for partitioning. Learn to define these keys, understand their impact on cluster data placement, and enhance query performance by avoiding unbalanced partitions and hotspots in distributed databases.
We'll cover the following...
The primary key is a crucial component of the Apache Cassandra data model, serving two essential functions:
It ensures the uniqueness of each record.
It determines the record’s placement within the cluster.
In Cassandra, a table’s primary key consists of one or more partition keys and zero or more clustering columns, with the partition key(s) always listed first in the primary key definition.
In Apache Cassandra, a table’s primary key cannot be altered. Modifying the primary key is not allowed as it determines how table data is distributed across the cluster and how it is stored on disk.
Partition key
The partition key is part of the primary key that defines where the record resides in the cluster. It is used for locating the node where the record is to be read from/written. A partition is a set of rows that have the same value for their partition key. A single-column partition key is referred to as a simple partition key.
Composite partition key
A composite partition key comprises multiple columns and forms a logical grouping inside a partition. It uses two or more columns to identify where the data will reside in the cluster. To define a composite partition key, the columns need to be enclosed in parentheses.