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Index Considerations and Management

On this page

  • Overview
  • Operational Considerations
  • Sample Data
  • Create an Index
  • List Indexes
  • Remove an Index
  • Delete a Single Index
  • Delete All Indexes
  • API Documentation

In this guide, you can learn about using indexes to improve the efficiency of your queries and add functionality to querying and storing documents.

Without a relevant index, MongoDB scans every document in a collection to find the documents that match a query. These collection scans are slow and can negatively affect the performance of your application. However, if the appropriate index exists, MongoDB can use the index to reduce the number of documents to inspect.

To improve query performance, build indexes on fields that appear often in your application's queries or operations that return sorted results. Each index that you add consumes disk space and memory, so we recommend that you track memory and disk usage when doing 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.

To learn more about designing your data model and choosing indexes, see the Indexes section of the Operational Factors and Data Models guide in the MongoDB Server manual.

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.

MongoDB supports several index types to help query your data. The following pages describe different index types and provide sample code to programmatically create each type of index.

  • Single Field Indexes

  • Compound Indexes

  • Multikey Indexes

  • Atlas Search Indexes

You can retrieve a list of indexes on a collection by calling the MongoDB\Collection::listIndexes() method:

foreach ($collection->listIndexes() as $indexInfo) {
echo $indexInfo;
}

You can remove any unused index except the default unique index on the _id field.

The following sections provide examples that show how to remove one or more indexes from a collection.

Pass the name of an index to the MongoDB\Collection::dropIndex() method to remove an index from a collection.

The following example removes the '_title_' index from the movies collection:

$collection->dropIndex('_title_');

Note

You cannot remove a single field from a compound index. You must drop the entire index and create a new one to update the indexed fields.

You can delete all indexes by calling the MongoDB\Collection::dropIndexes() method on a collection:

$collection->dropIndexes();

The dropIndexes() method returns information about the number of indexes removed and a success message.

To learn more about any of the methods or types discussed in this guide, see the following API documentation:

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Optimize Queries by Using Indexes