Postgres EXPLAIN ANALYZE lies about buffers unless you ask

EXPLAIN ANALYZE shows timings but not I/O by default. To see what's actually being read from disk vs. cached, you need:

EXPLAIN (ANALYZE, BUFFERS, FORMAT TEXT)
SELECT * FROM users WHERE email = 'x@y.com';

The Buffers: line tells you shared hit=N read=N — that "read" is your real disk I/O. A query that's "fast" in EXPLAIN can still hammer the disk if you don't check this.

Pair with track_io_timing = on in postgresql.conf for actual I/O latency.