Work with Indexes
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Overview
In this guide, you can learn how to use indexes with the Kotlin Sync driver. Indexes can improve the efficiency of queries and add functionality to querying and storing documents.
Without indexes, MongoDB must scan every document in a collection to find the documents that match each query. These collection scans are slow and can negatively affect the performance of your application. However, if an appropriate index exists for a query, MongoDB can use the index to limit the documents it must inspect.
Operational Considerations
To improve query performance, build indexes on fields that appear often in your application's queries and operations that return sorted results. Each index that you add consumes disk space and memory when active, so we recommend that you track index memory and disk usage for capacity planning. In addition, when a write operation updates an indexed field, MongoDB updates the related index, which can negatively impact performance for write operations.
You can use wildcard indexes in your MongoDB application to query against fields whose names are not known in advance or are arbitrary. Wildcard indexes are not designed to replace workload-based index planning.
For more information about designing your data model and choosing indexes appropriate for your application, see the Data Modeling and Indexes guide in the MongoDB Server manual.
Sample Data
The examples in this guide use the movies collection in the sample_mflix
database from the Atlas sample datasets. To learn how to create a
free MongoDB Atlas cluster and load the sample datasets, see the
Get Started with Atlas guide.
Create an Index
MongoDB supports several different index types to help query your data. The following pages describe the most common index types and provide sample code for creating each index type.
Remove an Index
You can remove any unused index except the default unique index on the
_id field.
The following sections show how to remove a single index or how to remove all indexes in a collection.
Delete a Single Index
Pass an index name to the dropIndex() method to remove an index from a collection.
The following example removes an index with the name "_title_" from the movies
collection:
collection.dropIndex("_title_")
Note
You cannot remove a single field from a compound text index. You must drop the entire index and create a new one to update the indexed fields.
Delete All Indexes
You can drop all indexes by calling the dropIndexes() method on your collection:
collection.dropIndexes()
API Documentation
To learn more about any of the methods or types discussed in this guide, see the following API documentation: