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Performance Implications

Learning Focus

Use this lesson to understand how type choices affect indexes, casts, and planner decisions in PostgreSQL.

Concept Overview​

Performance impacts show up through:

  • index selection and size
  • operator support (what can be indexed)
  • implicit/explicit casts
  • statistics and selectivity

Practical Guidelines​

  • Use consistent types for join keys (avoid casts in joins).
  • Avoid functions on filter columns unless you have expression indexes.
  • Use timestamptz for event times; time range queries should be index-friendly.

Example: expression index for case-insensitive lookup:

CREATE INDEX idx_users_email_lower ON users (lower(email));
SELECT * FROM users WHERE lower(email) = lower('dev@example.com');

Best Practices​

  • Start from query patterns and validate with EXPLAIN.
  • Keep joins type-aligned.
  • Measure before and after schema changes.

What's Next​