What Is a Partial Indexes in PostgreSQL?
A partial index stores entries only for rows satisfying its WHERE predicate. The planner must prove query conditions imply that predicate.
How the Partial Indexes Algorithm Works
A partial index stores entries only for rows satisfying its WHERE predicate. The planner must prove query conditions imply that predicate.
When to Use Partial Indexes
Stable hot subsets such as ready jobs, active accounts, or rows with a particular status.
How to Create a PostgreSQL Partial Indexes
Review data quality, existing structures, feature support, build time, and deployment requirements before creating an index on a production table.
CREATE INDEX jobs_ready_idx ON jobs (run_at) WHERE state = 'ready';Partial Indexes Query Example
This example demonstrates the matching query shape. Check the execution plan to confirm that the engine can use the index.
SELECT id FROM jobs WHERE state = 'ready' AND run_at <= now() ORDER BY run_at LIMIT 50;Queries Supported by Partial Indexes
Stable hot subsets such as ready jobs, active accounts, or rows with a particular status. A similar-looking predicate may not use the same access path; operators, expressions, key order, and data type all matter.
Read Performance, Storage, and Write Costs
Smaller for excluded rows, but queries unable to imply its predicate cannot use it for complete results. Indexes reduce some search work but require storage and add maintenance to writes.
Partial Indexes Limitations and Common Mistakes
Parameterized or differently expressed predicates may prevent the planner from proving applicability.
Do not assume that an index being present means the optimizer chose it or that the query became selective.
How to Measure and Tune Partial Indexes
Use EXPLAIN with exact application SQL; keep the predicate selective and aligned with the hot subset.
Compare representative plans and timings before and after, including concurrent writes and realistic data volumes.
Partial Indexes Questions
Will the database always use this index?
No. The optimizer weighs selectivity, estimated costs, statistics, cache state, and the amount of data returned.
What should I verify before production?
Confirm version support, query compatibility, write overhead, build/rollback procedures, and index behavior during backup and recovery.
Official PostgreSQL Index Documentation
Check PostgreSQL documentation: Index Types for release-specific requirements and supported operators.