Hive’s Cost-Based Optimization (CBO) is a powerful feature that enables Hive to optimize queries based on the estimated cost of each query plan. By analyzing the data statistics and the query structure, Hive’s CBO can generate more efficient query plans that can significantly improve query performance.
Role of Hive CBO:
Hive’s CBO works by analyzing the data statistics and the query structure to generate an estimated cost for each query plan. The cost estimation takes into account factors such as the size of the data, the complexity of the query, and the resources required to execute the query. Based on the estimated cost, Hive’s CBO can select the most efficient query plan for a given query, which can significantly improve query performance.
Hive’s CBO is particularly useful for complex queries that involve multiple joins, subqueries, or aggregates. By generating more efficient query plans, Hive’s CBO can reduce the execution time of these queries and improve overall query performance.
Enabling Hive CBO:
To enable Hive’s CBO, you must first set the following configuration properties in your Hive session:
hive.cbo.enable=true
hive.stats.autogather=true
hive.compute.query.using.stats=true
These configuration properties enable Hive’s CBO and allow Hive to gather data statistics and use them in the cost estimation process.
Once Hive’s CBO is enabled, you can use the “EXPLAIN” command to generate a query plan for your query. The query plan will include information about the estimated cost of each query plan and the selected query plan.
For example, the following query enables Hive’s CBO and generates a query plan for a simple query:
SET hive.cbo.enable=true;
SET hive.stats.autogather=true;
SET hive.compute.query.using.stats=true;
EXPLAIN SELECT * FROM my_table WHERE my_column = 'value';The resulting query plan will include information about the estimated cost of each query plan and the selected query plan.
Hive’s Cost-Based Optimization (CBO) is a powerful feature that can significantly improve query performance by generating more efficient query plans. By enabling Hive’s CBO and using the “EXPLAIN” command to generate query plans, you can optimize your queries and reduce the execution time of complex queries. When designing your Hive queries, it is important to consider the role of Hive’s CBO and choose the appropriate optimization techniques to ensure that your queries run efficiently and deliver the results you need.
Hive important pages to refer
