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- Create a Hashed Index
Create a Hashed Index¶
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New in version 2.4.
Hashed indexes compute a hash of the value of a field in a collection and index the hashed value. These indexes permit equality queries and may be suitable shard keys for some collections.
Tip
MongoDB automatically computes the hashes when resolving queries using hashed indexes. Applications do not need to compute hashes.
See
Hashed Shard Keys for more information about hashed indexes in sharded clusters, as well as Index Concepts and Indexing Tutorials for more information about indexes.
Procedure¶
To create a hashed index, specify
hashed
as the value of the index key, as in the following
example:
Example
Specify a hashed index on _id
Considerations¶
MongoDB supports hashed
indexes of any single field. The hashing
function collapses embedded documents and computes the hash for the entire
value, but does not support multi-key (i.e. arrays) indexes.
You may not create compound indexes that have hashed
index fields.