PostgreSQL 19 adds EXPLAIN (ANALYZE, IO) for I/O statistics

PostgreSQL 19 introduces the IO option for EXPLAIN, exposing read-stream behavior: prefetch depth, physical I/O request counts, sizes and concurrency. The feature was demoed at pgconf.eu with contributions from Microsoft engineers.

• EXPLAIN (ANALYZE, IO) reports Prefetch avg, max and capacity of the read stream
• The I/O line shows count, waits, size and in-progress concurrent requests
• In the demo, 29,145 block reads were merged into 1,825 I/O requests of ~16 blocks
• Only 7 of 1,825 requests were unfinished when the scan needed them