What is the optimizer in Spark?

In Spark, the optimizer is the component responsible for optimizing and improving the execution plan of a query. It selects the best execution plan to enhance the performance and efficiency of the query. Commonly used optimizers in Spark include rule-based optimizers (such as predicate pushdown, projection elimination, etc.) and cost-based optimizers (such as cost estimation, join order selection, etc.). By utilizing the optimizer, Spark can better utilize computational and storage resources, speeding up the execution process of queries.