MongoDB Special indexes

 

Capped Collections

// Create capped collection (100000 bytes and max 10 entries)

> db.createCollection("ring_buffer",{"capped":true,"size":100000,"max":10})

{ "ok" : 1 }

// insert more than 10 messages

> db.ring_buffer.insert({"message":1})

WriteResult({ "nInserted" : 1 })

> db.ring_buffer.insert({"message":2})

WriteResult({ "nInserted" : 1 })

> db.ring_buffer.insert({"message":3})

WriteResult({ "nInserted" : 1 })

> db.ring_buffer.insert({"message":4})

WriteResult({ "nInserted" : 1 })

> db.ring_buffer.insert({"message":5})

WriteResult({ "nInserted" : 1 })

> db.ring_buffer.insert({"message":6})

WriteResult({ "nInserted" : 1 })

> db.ring_buffer.insert({"message":7})

WriteResult({ "nInserted" : 1 })

> db.ring_buffer.insert({"message":8})

WriteResult({ "nInserted" : 1 })

> db.ring_buffer.insert({"message":9})

WriteResult({ "nInserted" : 1 })

> db.ring_buffer.insert({"message":10})

WriteResult({ "nInserted" : 1 })

> db.ring_buffer.insert({"message":11})

WriteResult({ "nInserted" : 1 })

// list collection, only rest 10 entries

> db.ring_buffer.find()

{ "_id" : ObjectId("5f7d7b1b4db79b5cc8c54240"), "message" : 2 }

{ "_id" : ObjectId("5f7d7b1d4db79b5cc8c54241"), "message" : 3 }

{ "_id" : ObjectId("5f7d7b204db79b5cc8c54242"), "message" : 4 }

{ "_id" : ObjectId("5f7d7b234db79b5cc8c54243"), "message" : 5 }

{ "_id" : ObjectId("5f7d7b264db79b5cc8c54244"), "message" : 6 }

{ "_id" : ObjectId("5f7d7b274db79b5cc8c54245"), "message" : 7 }

{ "_id" : ObjectId("5f7d7b2a4db79b5cc8c54246"), "message" : 8 }

{ "_id" : ObjectId("5f7d7b2c4db79b5cc8c54247"), "message" : 9 }

{ "_id" : ObjectId("5f7d7b2e4db79b5cc8c54248"), "message" : 10 }

{ "_id" : ObjectId("5f7d7b304db79b5cc8c54249"), "message" : 11 }

Time-To-Live Indexes

Time-To-Live index need config in Date data type.

After “expireAfterSeconds”, the data will be deleted

// create index for Date type with “expireAfterSeconds” attributes

> db.users.createIndex({"date":1},{"expireAfterSeconds":5})

{

    "createdCollectionAutomatically" : false,

    "numIndexesBefore" : 1,

    "numIndexesAfter" : 2,

    "ok" : 1

}

// update users with date

> db.users.updateOne({"name":"user164"},{"$set":{"date":new Date()}})

{ "acknowledged" : true, "matchedCount" : 1, "modifiedCount" : 1 }

// after 5 seconds, the records will be deleted