What Is a Wildcard Indexes in MongoDB?
Indexes many or all field paths under a flexible schema, allowing queries on fields whose names are not known in advance.
How the Wildcard Indexes Algorithm Works
Indexes many or all field paths under a flexible schema, allowing queries on fields whose names are not known in advance.
When to Use Wildcard Indexes
Heterogeneous documents or user-defined attributes with unpredictable field names.
How to Create a MongoDB Wildcard Indexes
Review data quality, existing structures, feature support, build time, and deployment requirements before creating an index on a production table.
db.events.createIndex({ "$**": 1 })Wildcard Indexes Query Example
This example demonstrates the matching query shape. Check the execution plan to confirm that the engine can use the index.
db.events.find({ "attributes.deviceType": "sensor" })Queries Supported by Wildcard Indexes
Heterogeneous documents or user-defined attributes with unpredictable field names. 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
Broader indexes can be less efficient and larger than focused indexes; restrictions apply to compound use. Indexes reduce some search work but require storage and add maintenance to writes.
Wildcard Indexes Limitations and Common Mistakes
Wildcard indexes do not make arbitrary document queries free; path and projection behavior is constrained.
Do not assume that an index being present means the optimizer chose it or that the query became selective.
How to Measure and Tune Wildcard Indexes
Prefer path-scoped wildcard indexes; replace high-value paths with targeted indexes when schema stabilizes.
Compare representative plans and timings before and after, including concurrent writes and realistic data volumes.
Wildcard 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.