Introduction to MongoDB collection.hideIndex() Method

The hideIndex() method is used to hide a specific index in a specified collection. This means that the index will no longer be used in queries. However, the index still exists in the collection and can be re-enabled when needed. This method is only available in MongoDB 4.4 or later.

Syntax

hideIndex(<collectionName>, <indexName>)

Where collectionName is the name of the collection and indexName is the name of the index to be hidden.

Use Cases

In some situations, it may be necessary to hide an index in order to better understand the performance bottleneck of a query. For example, you may want to temporarily hide a large compound index to test whether a single-field index is more suitable for some queries.

Example

Assuming we have a collection named users with a compound index named username_1_email_1. Here’s how to use the hideIndex() method to hide the index:

db.users.hideIndex("username_1_email_1")

This will hide the username_1_email_1 index in the collection.

To view the list of indexes in the collection, use the getIndexes() method:

db.users.getIndexes()

Here’s an example output:

[
  {
    "v": 2,
    "key": {
      "_id": 1
    },
    "name": "_id_",
    "ns": "test.users"
  },
  {
    "v": 2,
    "unique": true,
    "key": {
      "username": 1,
      "email": 1
    },
    "name": "username_1_email_1",
    "ns": "test.users"
  }
]

In the above output, we can see that the username_1_email_1 index has been hidden. If you need to re-enable the index, you can use the unhideIndex() method:

db.users.unhideIndex("username_1_email_1")

Conclusion

The hideIndex() method provides a simple way to temporarily hide an index in order to better understand the performance bottleneck of a query. However, it should be noted that this method only hides the index and the index still exists in the collection and can be re-enabled when needed.