Pipelining in PostgreSQL allows clients to send multiple queries without waiting for the results of previous ones, significantly improving throughput. Introduced in PostgreSQL 18, this feature enhances the efficiency of query processing, especially when dealing with large batches of data across different network types. Performance tests indicate substantial speed gains, underscoring the benefits of utilizing pipelining in SQL operations.

SQL query optimization involves the DBMS determining the most efficient plan to execute a query, with the query optimizer responsible for evaluating different execution plans based on cost. The Plan Explorer tool, implemented for PostgreSQL, visualizes these plans and provides insights into the optimizer's decisions by generating various diagrams. The tool can operate in both standalone and server modes, enabling deeper analysis of query execution and costs.