expiring-data

TTL Collection

There are times when we need to remove data in a Mongo collection after a specific time. This example shows how we can remove expired data using MongoDB TTL indexing.

Notes

1. MongoDB runs the TTLMonitor on a separate thread that looks for TTL indexes in all collections.
2. By default, the TTLMonitor runs every 60 seconds. Read here for more information.
3. To enable TTLMonitor in our MongoDB service, the file setup-ttl.js is created and mounted on the Mongo container. The file will be ingested and executed by Mongo during boot-up to enable TTLMonitor.
4. It's important that the time field of the TTL index is set to is of type time.Time, any other data types will not trigger the object to be removed after expiration.
5. Since the code includes dropping a collection, we added an dbAdmin role to the user - see create-user.js.

Setup

1. Launch a shell session and start MongoDB (server) via Docker:

   $ docker-compose up

2. Run Go program.

   $ go run ./main.go

3. You can connect to Mongo via the console and see that a token object that is set to expire in a minute, was inserted to the collection tokens.

   $ docker exec -it mongo mongo -u nobody -p secrets go-recipes
   > db.tokens.find()
   { "_id" : ObjectId("5ffff0bd4130100b939e597d"), "value" : "SomeSecretValue", "expireAt" : ISODate("2021-01-14T07:21:29.593Z") }
   > // Wait for a little more than 60 seconds
   > db.tokens.find()
   > // The object has expired and removed

4. Tear down the mongo docker container when done.

   $ docker-compose down

5. Alternatively, you can run everything with just 2 commands.

   $ make run
   $ make teardown    # Run this to remove containers

Reference and Credits

• MongoDB Go Driver API Guide
• Expire Data from Collections by Setting TTL
• Working with MongoDB TTL Index