MongoDB - Indexing Limitations

In this chapter, we will learn about Indexing Limitations and its other components.

Extra Overhead

Every index occupies some space as well as causes an overhead on each insert, update and delete. So if you rarely use your collection for read operations, it makes sense not to use indexes.

note

• Indexes require additional space.
• Each insert, update, and delete operation requires additional processing due to index maintenance.

RAM Usage

Since indexes are stored in RAM, you should make sure that the total size of the index does not exceed the RAM limit. If the total size increases the RAM size, it will start deleting some indexes, causing performance loss.

note

Ensure that the total size of all indexes does not exceed the available RAM to avoid performance issues.

Query Limitations

Indexing can't be used in queries which use:

• Regular expressions or negation operators like $nin, $not, etc.
• Arithmetic operators like $mod, etc.
• $where clause

note

• Regular expressions and negation operators cannot use indexes.
• Arithmetic operators and $where clause cannot use indexes.

Query Type	Index Usage
Regular Expressions	Not Supported
Negation Operators	Not Supported
Arithmetic Operators	Not Supported
$where Clause	Not Supported

Index Key Limits

Starting from version 2.6, MongoDB will not create an index if the value of existing index field exceeds the index key limit.

Note: Index creation is restricted if any field value exceeds the index key limit.

Inserting Documents Exceeding Index Key Limit

MongoDB will not insert any document into an indexed collection if the indexed field value of this document exceeds the index key limit. The same is the case with mongorestore and mongoimport utilities.

note

Documents with indexed field values exceeding the key limit will not be inserted into an indexed collection.

Maximum Ranges

• A collection cannot have more than 64 indexes.
• The length of the index name cannot be longer than 125 characters.
• A compound index can have a maximum of 31 fields indexed.

Table: Maximum Ranges

Limit Type	Maximum Value
Number of Indexes	64
Length of Index Name	125 Characters
Fields in Compound Index	31 Fields