What is the optimizer in Spark used for?

The optimizer in Spark is used to improve query performance by optimizing the execution plan. It can select the appropriate execution plan based on factors such as query complexity and data distribution, in order to reduce query execution time and resource consumption. The optimizer typically considers various optimization strategies such as predicate pushdown, projection pruning, and join resolution to enhance query efficiency. Through optimization by the optimizer, query execution on Spark can be made more efficient.