Let’s Learn Together

Ted M. Young @jittertedDeveloper & Agile Coach

Guidewire Software, San Mateo, CA

Intro to CQRS

Silicon Valley Code Camp – October 9, 2011

Creative Commons Attribution-ShareAlike (CC BY-SA 3.0)

What’s the Problem

CAPConsistencyAvailabilityPartitionability

Can’t Have All Three

CAP: Choose TwoConsistency + Availability

Sacrifice PartitionabilityE.g., single database, clustered database

Consistency + PartitionabilitySacrifice AvailabilityE.g., pessimistic locking, distributed locking

Availability + PartitionabilitySacrifice ConsistencyE.g., optimistic locking, merging, expirationsMany systems are like this: eventually consistent

Whether you like it or not

BASE vs. ACID

Basically AvailableSoft-stateEventual consistency

Stale data is OK

What’s so bad about

Eventual Consistency

BASE is Not New

Inktomi Presentation in 1998

Not an either-or, but a spectrum

BASE vs. ACID

CQRS

Leans to BASE

CQRS is

Command Query Responsibility Segregation

http://www.udidahan.com/2009/12/09/clarified-cqrs/

Command

Mutator

Re-think UI

No more CRUD?

Stop The Forms

Query

With respect to the queried data

Read-Only

Resources: CAP, Other BackgroundBertrand Meyer

Command-Query Separation, §23.1 (p. 751)Object-Oriented Software Construction, 2nd Ed. (ISBN 0136291554)

Dr. Eric Brewer, InktomiPresentation (1998)

http://www09.sigmod.org/disc/disc99/disc/nsf_acad_ind/brewer/sld019.htm

Dan PritchettBASE and latency

http://www.infoq.com/articles/pritchett-latency

Prevaylerhttp://prevayler.org/old_wiki/Welcome.html

Resources: CQRS-Specific

Greg Young (no relation)

CQRS and CAPhttp://codebetter.com/gregyoung/2010/02/20/cqrs-and-cap-theorem/

Udi DahanGood overview

http://www.udidahan.com/2009/12/09/clarified-cqrs/

Martin Fowler’s CQRShttp://martinfowler.com/bliki/CQRS.html

Axon Framework (Java)http://www.axonframework.org

Resources: CQRS-Specific

Rinat AbdullinCQRS Starting Page

http://abdullin.com/cqrs/More useful info from Rinat with good PDF diagram

http://abdullin.com/xlim/

Pål FossmoAnother nice blog entry on CQRS

http://blog.fossmo.net/post/Command-and-Query-Responsibility-Segregation-%28CQRS%29.aspx

Thanks!

Follow me on Twitter: @jittertedEmail me: tyoung@guidewire.com

[Guidewire is hiring devs and testers!]

Final Questions?