Tutorials System Design Tutorial
Query Optimization for Production Databases — Complete Guide
Query Optimization for Production Databases — Complete Guide: free step-by-step lesson with examples, common mistakes, and interview tips — part of System Design Tutorial on Toolliyo Academy.
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System Design Tutorial · Lesson 82 of 100
Query Optimization for Production Databases
Basics ✓ → Scale ✓ → Interview
Interview · 3 — Case studies · ~10 min · Module 9: Performance and Optimization
What is this?
Production query optimization is continuous — plans, indexes, hot queries, and guarding OLTP from analytical abuse.
Why should you care?
ShopNest sale-day surprises often come from a new query shape, not from “random slowness.”
See it live — copy this example
Sketch the architecture on paper. These lessons focus on concepts and trade-offs.
Tooling: slow query log / Query Store
Top offenders by total time
Fix: index, rewrite, cache, or move to replica
Gate: explain plans on risky PR SQLRun Example »
This lesson uses terminal or setup steps. Run commands on your computer — the live editor appears on coding lessons.
What happened?
- Rank queries by total impact.
- Prefer indexes and rewrites.
- Isolate analytics.
- Make risky SQL reviewable in PRs.
Practice next
- List top 5 ShopNest queries by time.
- Add or adjust one index carefully.
- Move one report to a replica.
- Alert when a query’s p95 doubles after deploy.
- Kill N+1 in a hot endpoint.
Remember
Rank by impact. Fix or relocate. Review risky SQL.
Query Store regression catch
ShopNest spots a plan flip after release.
Outcome: Rollback/force good plan; then permanent fix.
Interview prep for this lesson
Practice these questions aloud after reading—each links to a full structured answer.
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