Time to Live (TTL) is a feature in MongoDB that allows you to automatically expire documents after a specified amount of time. This is useful for scenarios where you want to keep data for a limited duration, such as temporary data, session data, or cache entries.
How TTL works:
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Index creation: To enable TTL for a collection, you create an index on a field that represents the expiration time. This field must be of type
Date.
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Expiration time setting: When creating the index, you specify the TTL value in seconds.
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Document expiration: MongoDB periodically scans the collection and deletes documents whose expiration time has passed.
Example:
db.sessions.createIndex({ expiresAt: 1 }, { expireAfterSeconds: 3600 });This creates an index on the expiresAt field and sets the TTL to 1 hour (3600 seconds). Any documents in the sessions collection with an expiresAt value that is older than 1 hour will be automatically deleted.
Use cases for TTL:
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Session management: Store session data with a TTL to automatically expire inactive sessions.
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Temporary data: Keep temporary data for a limited time, such as cached results or temporary files.
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Data retention policies: Implement data retention policies by setting appropriate TTL values for different types of data.