TTL (Time To Live)

Time to Live (TTL) in MongoDB Introduction

Time to Live (TTL) is a feature in MongoDB that allows for the automatic deletion of documents after a specified period. TTL indexes are special indexes that MongoDB uses to remove expired documents from a collection automatically. This is particularly useful for applications that need to manage data retention and cleanup old data efficiently.

How TTL Indexes Work A TTL index in MongoDB is a single-field index that MongoDB uses to automatically delete documents from a collection once they reach a specified age. This age is determined based on the value of a date field in the documents.

Key Concepts:

Expiration Field: The field in the document that holds the date and time when the document should expire.

TTL Index: An index created on the expiration field, specifying the number of seconds after which the document should be considered expired.

Creating a TTL Index To create a TTL index, you need to use the createIndex method with the expireAfterSeconds option.

Step-by-Step Guide:

Insert Documents with a Date Field: Ensure your documents include a date field that MongoDB will use to determine the expiration time.

db.myCollection.insertMany([
   { "item": "item1", "createdAt": new Date() },
   { "item": "item2", "createdAt": new Date() }
 ]);

Create the TTL Index: Create an index on the date field with the expireAfterSeconds option. For example, to expire documents 3600 seconds (1 hour) after the createdAt field value:

db.myCollection.createIndex({ "createdAt": 1 }, { expireAfterSeconds: 3600 });

This command tells MongoDB to delete documents from myCollection once the createdAt field is older than 3600 seconds.

Examples: Example 1: Expiring Documents after One Hour

Insert Documents:

 db.sessions.insertOne({
   "sessionId": "abc123",
   "createdAt": new Date()
 });

Create TTL Index: