Science of mongodb

The Science ofMongoDB @ethangunderson MongoDC 2011

Hiring

1)CAP?2)What does MongoDB do about it?3)Compare and Contrast4)ACID?5)How it relates to MongoDB

Questions?Comments?Shout Out!

CAP Theorem

Eric Brewer

ConsistencyAvailabilityPartition Tolerance

Consistency All clients have thesame view of the data

AvailabilityAll clients have access to all data

Partition Tolerance The system’s properties hold true in the case of partitions

Pick Two

CAThis is not a real option.

You Canʼt SacriﬁcePartition Tolerance http://codahale.com/you- cant-sacriﬁce-partition- tolerance/

When a failure happens, what am I sacriﬁcing? Consistency or Availability?

CP The system sacriﬁces availability in order tomaintain data consistency

AP The system sacriﬁcesconsistency to ensure the most uptime as possible

What is Mongo?

CPSince, by default, Mongo routes all requests to a master, it is strongly consistent

MasterSlave Slave

Replica Set Replica Set

Optionally AP

Master Client:slaveOK Slave Slave

(Amazon Dynamo)

AP As long as one node isup, the cluster can service read/write requests

foo: 12foo: nil foo: 35

AtomicityAll transactions are “all or nothing”

Consistency All transactions takethe database from onevalid state to the next

Isolation Transactions cannotaccess data modiﬁed in another uncompleted transaction

DurabilityThe ability to recovercommitted transaction updates

Consistency !=Consistency

Thanks!

by Ethan Gunderson