EXPLAIN, ANALYZE, and Verify Index Usage

EXPLAIN (ANALYZE, BUFFERS) SELECT * FROM users WHERE email = 'a@example.com';

# See actual runtime, loops, and buffer reads.

EXPLAIN SELECT * FROM users WHERE email = 'a@example.com';

# Inspect access path and chosen key.

EXPLAIN QUERY PLAN SELECT * FROM users WHERE email = 'a@example.com';

# Inspect scans versus indexed searches.

db.users.find({ email: 'a@example.com' }).explain('executionStats')

# Check keys examined and docs examined.

Look for:
- indexed search instead of full scan
- fewer rows/docs examined
- fewer extra sorts
- lower latency under realistic load
- acceptable write overhead

# A quick review checklist after creating an index.