Key takeaway
Single-column indexes, composite indexes, leftmost prefix rules, covering indexes, and write overhead. Start with the related games below when you want to turn the definition into practice.
Why this matters
Indexes are one of the highest leverage tools for making backend queries predictable under load.
How to practice
Match equality filters, sort order, range predicates, and selected columns deliberately.
0 active misses 0 reviewed 0 games completed
Learning objectives
- Choose indexes that match filters and ordering.
- Apply the leftmost prefix rule for composite indexes.
- Recognize when an index is low-value or creates unnecessary write overhead.
- Compare estimated and actual plan rows.
- Connect selectivity to scan and join choices.
- Validate query changes across representative workloads.
Common mistakes to avoid
- Indexing a low-cardinality boolean column by itself and expecting a large speedup.
- Creating composite indexes in the wrong column order.
- Ignoring ORDER BY and then paying for a separate sort.
- Reading cost as elapsed milliseconds.
- Adding indexes without checking selectivity.
- Validating only one parameter value.
Games for SQL Indexes
Start with the first game, then use local review history to revisit missed decisions.
Databases Intermediate
Choose the best database index for simplified schemas and queries while learning full scans, covering indexes, sort avoidance, and composite order.
- Time
- 7-10 minutes
- Concept
- Database indexing and query performance
- Data & Performance
- Algorithmic Reasoning
- SQL
- indexes
- performance
Play SQL Index Quest Databases Advanced
Investigate PostgreSQL query plans, cardinality gaps, scan choices, join amplification, and rollout evidence.
- Time
- 9-12 minutes
- Concept
- SQL query planning and cardinality
- Data & Performance
- SQL Indexes
- Performance
- Databases
Play Query Plan Investigator Databases Advanced
Choose composite and partial indexes while accounting for MVCC churn, bloat, and partition lifecycle.
- Time
- 8-11 minutes
- Concept
- Index and storage strategy
- Data & Performance
- SQL Indexes
- MVCC
- Databases
Play Index & Storage Strategy Lab Reliability Advanced
Triage blocking chains, slow-query regressions, expand-contract changes, and resource-safe database rollouts.
- Time
- 10-12 minutes
- Concept
- Production database incident response
- Data & Performance
- Databases
- Incidents
- Schema Migrations
Play Slow Query & Change War Room Spring Advanced
Place Spring transactions, JPA fetch plans, rollback rules, and validated configuration at production boundaries.
- Time
- 9-11 minutes
- Concept
- Spring transaction and data boundaries
- Spring Production
- Transactions
- SQL Indexes
- Spring
Play Spring Data Boundary Clinic Databases Intermediate
Choose safe zero-downtime database migration steps for expanding schemas, backfilling data, rolling out indexes, enforcing constraints, and recovering from failures.
- Time
- 6-9 minutes
- Concept
- Zero-downtime schema migration planning and expand-contract releases
- Data & Performance
- Database Reliability
- migrations
- schema design
- backfill
Play Schema Migration Runbook Databases Advanced
Defend database invariants from concurrent requests by choosing transactions, locks, constraints, snapshot reads, and optimistic concurrency.
- Time
- 7-10 minutes
- Concept
- Database transactions, isolation anomalies, locks, and invariant protection
- Data & Performance
- Database Reliability
- SQL
- transactions
- isolation
Play Transaction Isolation Arena