Query Optimizer

Definitions

1. The database subsystem that transforms a parsed SQL query into an efficient execution plan by evaluating strategies like join ordering, index selection, and predicate pushdown based on table statistics and cost models. The optimizer chooses between plans (e.g., nested-loop vs. hash join) to minimize estimated I/O and CPU cost.

   In plain English: The part of a database that figures out the fastest way to answer your question, like choosing which shortcut to take through the data.

   Example: "The query was doing a full table scan until we ran ANALYZE — once the optimizer had fresh statistics it picked the composite index."

Related Terms

• materialized view
• Query
• Table
• Connection Pooling
• N+1 Query Problem
• Query Plan
• Index Scan vs Seq Scan
• Partitioning
• Query Engine