Code Recap: Tools for Optimizing Indexes

Below is the code used to run the explain() method in mongosh to return an explain plan. An explain plan is a report that gives us information about possible plans for executing a query, including the winning plan that MongoDB selects.

Code

explain() Method

Use the explain() method, chained with the find() method to return the explain plan in mongosh.

db.collection.explain().find()

Example Query

This query is used to retrieve documents from the listingsAndReviews_big_collection collection for all documents that match on property_type and room_type that allow a specific range of nights to stay with at least 2 bedrooms. The results are then sorted by the number_of_reviews in descending order.

The explain() method is chained to this query with verbosity level set to executionStats. This will return an explain plan document in the terminal that will include execution stats for the winning plan.

db.listingsAndReviews_big_collection
.explain("executionStats")
.find(
{ property_type: 'House', room_type: 'Entire home/apt', minimum_nights: { $gt: '2' }
, 
maximum_nights: { $lte: '30' }, bedrooms: { $gte: 2 } 
})
.sort({ number_of_reviews: -1 })

Handling Indexes

Below are the code snippets used to work with Indexes in mongosh.

Use the createIndex database command to create an index on a collection with different properties.

This command creates an index on the email field only and stores the values in ascending order.

db.users.createIndex({ email: 1 })

This command creates an index on the email and the status fields and stores the values in ascending order.

db.users.createIndex({ email: 1, status: 1})

The getIndexes() command retrieves the indexes that exist on a specific collection.

db.users.getIndexes()

The hideIndex() command disables the email_1 index temporarily. The query planner ignores the index during execution, but it remains stored in the metadata and can be re-enabled later.

db.users.hideIndex("email_1")

The dropIndex() command permanently removes the email_1 index, reducing storage and maintenance overhead. Dropping unused indexes can optimize storage and enhance performance when irrelevant indexes are eliminated.

db.users.dropIndex("email_1")