What Is a Partial Indexes in MongoDB?
Indexes only documents that satisfy partialFilterExpression. Planner use requires the query to imply the index filter.
How the Partial Indexes Algorithm Works
Indexes only documents that satisfy partialFilterExpression. Planner use requires the query to imply the index filter.
When to Use Partial Indexes
Frequently read subsets such as open orders, active listings, or non-archived rows.
How to Create a MongoDB Partial Indexes
Review data quality, existing structures, feature support, build time, and deployment requirements before creating an index on a production table.
db.orders.createIndex({ createdAt: -1 }, { partialFilterExpression: { status: "open" } })Partial Indexes Query Example
This example demonstrates the matching query shape. Check the execution plan to confirm that the engine can use the index.
db.orders.find({ status: "open" }).sort({ createdAt: -1 }).limit(20)Queries Supported by Partial Indexes
Frequently read subsets such as open orders, active listings, or non-archived rows. 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
Queries outside the subset cannot use it to return complete results; filters support defined expressions. Indexes reduce some search work but require storage and add maintenance to writes.
Partial Indexes Limitations and Common Mistakes
A query must guarantee all matching documents are present in the partial index.
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
Compare the exact query predicate to the filter and verify with explain.
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 MongoDB Index Documentation
Check MongoDB documentation: Index Types for release-specific requirements and supported operators.