Capped Collection

1. Capped collection is fixed size collection when data is exceeded the maximum size, it deletes the old records.
2. An internally capped collection will maintain insertion order.
3. It uses circular buffers to clean up old data.
4. In realtime, if you want to log last 10days of logs we can go for Capped collection.

Create Capped collection

db.createCollection('logs', {capped:true, size:100000, max=2000}).

• In above quary, size indicates allocation of memory, max indicates max number of documents.

Update existing normal collection to Capped collection

db.runCommand({"convertToCapped": "users", size: 200000});

• But we have a problem with the capped collection is when data memory reaches max size or max number of documents it deletes old documents, it doesn't support time base delete.
• If we want to delete mongo documents based on the time we need to use TTL index based collection.

TTL index based Collection

1. TTL stands for Time To Leave.
2. TTL is a single field index on MongoDB collection.
3. After specific time MongoDB removes the documents from the collection.

Create TTL index

db.logs.createIndex({insertdDate:1}, { expireAfterSeconds: 100000 })

• In background expiry documents will be removed by MongoDB thread for every 60 seconds.