PostgreSQL Extended Query Protocol: Plan Reuse, Injection Prevention, and Pipelining

PostgreSQL’s extended query protocol splits a query into four messages—P (parse), B (bind), E (execute), and S (sync)—allowing the server to parse and analyze the SQL template once and reuse the plan for subsequent executions. The protocol introduces prepared statements, which cache the parse tree and analysis results, enabling plan reuse and reducing parsing overhead for repeated queries. Injection protection is achieved by separating the SQL template from the parameter values; values are sent in binary or text form and never parsed as SQL, preventing malicious input from being interpreted as code. The protocol also supports pipelining: multiple B/E pairs can be sent before a sync, allowing a batch of queries to be executed in a single round‑trip. PostgreSQL’s plan cache policy uses the first five executions to collect cost statistics, then compares custom and generic plans to decide which to cache, with the plan_cache_mode GUC controlling the behavior. Custom plans are recomputed on each execute, while generic plans are cached and reused, and the policy can be overridden with force_custom_plan or force_generic_plan. The extended protocol therefore improves performance, security, and network efficiency for high‑throughput applications.