Being mindful of query optimizer
summary
A migration checklist focused on measurable differences: DB2 compiles PL/SQL with semantic checks and stores executable plan in memory, PostgreSQL often defers semantic errors and replans every run unless you enable auto_explain; DB2 has optimization levels 0–9 while Postgres relies on stats (default_stats_target=100) and analyze/vacuum; use db2 explain table + db2exfmt or pg explain/analyze and visuals like Depesz; watch null behavior—Oracle may do a full table scan while Postgres does an index-only scan; historical failure rate cited ≈75–80% and a 10,000-row demo validates these differences.
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chapters (5)
- 0:00Introduction to query optimizers
- 2:55DB2 vs PostgreSQL optimizer differences
- 24:26Oracle optimizer explained
- 40:19Query optimization in practice
- 45:00Q&A session
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