Hive : Understanding the DISTRIBUTE BY Operator in Hive with an Example

One of the key features of Hive is its ability to optimize queries for improved performance. The DISTRIBUTE BY operator is one such optimization feature that can be used to enhance the performance of certain types of queries. In this article, we will dive deep into the DISTRIBUTE BY operator, its use cases, and walk through an example to understand its practical application.

What is the DISTRIBUTE BY Operator?

The DISTRIBUTE BY operator is used to redistribute the output rows from a MapReduce job in a more controlled manner. It allows users to specify the distribution key based on which the data should be distributed across the reducers. By doing so, it ensures that all rows with the same distribution key value go to the same reducer, providing an efficient way to group data without having to sort it.

Use Cases

The DISTRIBUTE BY operator is useful in the following scenarios:

1. When you want to perform a GROUP BY operation on a large dataset without sorting the data.
2. When you need to distribute the data evenly across reducers to prevent skew and improve performance.
3. When you want to control the partitioning of data in order to optimize join operations.

Example: Using the DISTRIBUTE BY Operator

In this example, we will use the DISTRIBUTE BY operator to analyze a sample dataset containing the details of fresh graduates. We will demonstrate how this operator can be used to efficiently group data and improve query performance.

Dataset Schema (freshers_in_details)

Now, let’s say we want to find the average CGPA of students in each branch without sorting the data. We can use the DISTRIBUTE BY operator to achieve this as follows:

CREATE TABLE freshers_in_avg_cgpa AS
SELECT branch, AVG(cgpa) as avg_cgpa
FROM freshers_in_details
DISTRIBUTE BY branch;