Covered query makes the execution of the query faster because indexes are stored in RAM or sequentially located on disk. It makes the execution of the query faster.
Covered query makes the fields are covered in the index itself, MongoDB can match the query condition as well as return the result fields using the same index without looking inside the documents.
A covered query in MongoDB refers to a query where all the fields that are part of the query are covered by an index, and the fields required by the query are present in the index itself. This means that MongoDB can fulfill the query using the index alone, without the need to examine the actual documents in the collection.
The importance of covered queries lies in their potential for improved performance. When a query can be satisfied by the index alone, MongoDB can avoid loading the actual documents from disk into memory, resulting in faster query execution. This is because the necessary data is already available in the index, and there is no need to fetch additional information from the documents themselves.
Key benefits of covered queries include:
- Reduced Disk I/O: Since MongoDB can use the index to satisfy the query, there is less need to read data from the disk, leading to reduced disk I/O operations.
- Faster Query Execution: With all the required data available in the index, the query can be processed more quickly, resulting in faster response times for the application.
- Optimized Memory Usage: Covered queries can help optimize memory usage because MongoDB does not need to load entire documents into memory when processing the query.
To achieve covered queries, it’s essential to create indexes that cover both the query criteria and the fields to be projected (returned) in the results. Proper index design is crucial for maximizing the benefits of covered queries in MongoDB.