With Big Data, comes well … a lot of data. But what if some of that data is only really useful within a certain timeframe?
Think about things like:
- User sessions
- Temporary tokens
- Logs and audit trails
- Time-sensitive cache
Luckily, MongoDB makes it easy to keep your collections tidy with what are called TTL indexes.
TTL (Time To Live) indexes automatically delete documents after a specified number of seconds and its as simple as adding a Date field (and index on that field) to your documents.
Let’s say we add a Date field called created to each document, and then we add a TTL index like so:
db.sessions.createIndex(
{ "created": 1 },
{ expireAfterSeconds: 3600 }
);MongoDB will then automatically remove (delete) any documents where created is older than 1 hour (which is 3600 seconds, if you don’t want to do the math). No manual cleanup jobs required!
Just make sure your date field is an actual Date object, not a string. You can find more about the Date type this helpful post: Quick Start: BSON Data Types – Date.
