Starting from MongoDB 4.4, we can now hide indexes from the query plan. This enables us to evaluate the potential impact of dropping an index without actually dropping the index.
If hiding it has a negative impact, we can unhide the index. This saves us from having to drop the index, then recreate it again.
Below are 3 ways to hide an index in MongoDB.
MongoDB provides several ways to drop an index or indexes.
To drop a single index, you can use the dropIndex() method.
To drop multiple indexes, you can use either the dropIndexes() method or the dropIndexes administration command.
In MongoDB, you can use the cursor.explain() method or the db.collection.explain() method to determine whether or not a query uses an index.
These methods enable you to view the query plan for the query, which includes whether or not it uses an index.
If you encounter the “index name must be a string” error when dropping multiple indexes in MongoDB, it’s probably because you’re passing the specifications document instead of the name.
When you use the dropIndexes() method or the dropIndexes command to drop multiple indexes, you need to pass the index names (not the specifications documents) in an array.
In MongoDB, when you create an index on a field that holds an array, it’s automatically created as a multikey index.
Multikey indexes support efficient queries against array fields.
Multikey indexes can be created for arrays that hold scalar data (e.g. strings, numbers, etc) and nested documents.
MongoDB provides the following geospatial index types that support geospatial queries.
2dsphere indexes support queries that calculate geometries on an earth-like sphere.In this article, I create a 2dsphere index.
When you create an index in MongoDB, if you don’t specify a name for it, MongoDB will assign one.
The default name consists of each indexed field name concatenated with the key value for that field. For example, the sort order, or if it’s a text index, the string _text, or if it’s a 2dsphere index, the string _2dsphere, etc.
But you can assign your own name when creating indexes in MongoDB.
When you create a wildcard index in MongoDB, you have the option of specifying a single field, all fields, or just some.
You also have the option of excluding certain fields. In other words, you can specify all fields except for one or more specific fields.
You can use the wildcardProjection parameter to include or exclude specific field paths from the wildcard index. This article presents an example of excluding specific fields in the wildcard index.
When you create a wildcard index in MongoDB, you have the option of specifying a single field, all fields, or just some.
You can use the wildcardProjection parameter to include or exclude specific field paths from the wildcard index. This article presents an example of including specific fields in the wildcard index.
When you create a text index in MongoDB, the index uses a default language of english.
The default language determines the rules to parse word roots (i.e. stemming) and ignore stop words.
However, you can change the default language if required.
You can also specify a language at the document level, and even at the subdocument level. The default language will only be used if a language hasn’t been specified at the document or subdocument level.
This article presents examples of specifying a language for a text index.