wunder beta📘 Keep index from meaning free speed
Indexes trade write cost and space for faster lookups — they are not free speed. B-trees, composites, and scan vs seek decide when they help.
3
lessons
~15 min
to learn
Adults
level
What you’ll learn
- Why scans hurtExplain scans vs selective indexes.Indexes are paid structures for real predicates.
- B-trees and compositesDescribe B-trees and composite order.Leftmost prefixes and leaf contents shape plans.
- Pay for what you queryJustify an indexing plan against write cost.Special indexes are specialists — explain is proof.
Grounded in trusted sources
- PostgreSQL documentation: Indexes
- Silberschatz, Korth, Sudarshan — Database System Concepts (indexing)
- B-tree index primers
- Query explain / planner reading notes
- Composite index leftmost-prefix guidance
- Write amplification / index maintenance context
Every Wunder lesson is built from real, reputable sources — never invented.
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