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A year with event sourcing and CQRS
The document presents a discussion on the concepts of Command Query Responsibility Segregation (CQRS) and Event Sourcing (ES) in software architecture, focusing on their advantages for developing high-performance systems and managing complex domains. It explains how CQRS evolves from Domain-Driven Design principles, while ES serves as an alternative storage pattern that emphasizes tracking changes over time rather than maintaining current state. The presentation highlights the potential applications and benefits of using these techniques in software development but also notes their challenges, particularly for junior developers.
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Similar to A year with event sourcing and CQRS
A year with event sourcing and CQRS
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- 12. A Year WithEvent Sourcing and CQRS Steve Pember CTO, ThirdChannel steve@thirdchannel.com Software Architecture Conf, 2016 THIRDCHANNEL @svpember
- 13. THIRDCHANNEL @svpember Agenda • CQRS •Event Sourcing • This Tech @ ThirdChannel • Demo
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- 15. Command - Query ResponsibilitySegregation
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- 20. –Eric Evans “Some objectsare not defined primarily by their attributes. They represent a thread of identity that runs through time and often across distinct representations. Sometimes such an object must be matched with another object even though attributes differ. An object must be distinguished from other objects even though they might have the same attributes.”
- 21. THIRDCHANNEL @svpember Domain DrivenDesign • Ubiquitous Language
- 22. THIRDCHANNEL @svpember Domain DrivenDesign • Ubiquitous Language • Entities / Value Objects
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- 25. THIRDCHANNEL @svpember Domain DrivenDesign • Ubiquitous Language • Entities / Value Objects • Aggregates
- 26. Group of Entitieswith one Root
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- 28. THIRDCHANNEL @svpember Domain DrivenDesign • Ubiquitous Language • Entities / Value Objects • Aggregates • Bounded Context
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- 30. Objects inside anAggregate may hold refs to other Roots
- 31. Deleting an Aggregatealso deletes dependents
- 32. Isolate related objectsinto Modules
- 33. Furthermore, No directcomms across boundaries
- 34. THIRDCHANNEL @svpember Domain DrivenDesign • Ubiquitous Language • Entities / Value Objects • Aggregates • Bounded Context • Domain Events
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- 38. CQRS is anEvolution on DDD
- 39. Basis: Two Objectswhere there was One
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- 41. But allows forInteresting and efficient Architectures
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- 44. Multiple Query Cachesderived from events
- 45. –Johnny Appleseed “Type aquote here.”
- 46. THIRDCHANNEL @svpember When shouldyou use CQRS?
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- 52. –Johnny Appleseed “Type aquote here.”
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- 55. THIRDCHANNEL @svpember Ok, sohow about Event Sourcing?
- 56. What do wedo with our Domain Events?
- 57. THIRDCHANNEL @svpember Event Sourcing •Alternative Storage Pattern - Save Deltas
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- 59. Store Deltas insteadof Current State
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- 61. Objects are backed- ‘sourced’ - by events
- 62. THIRDCHANNEL @svpember Event Sourcing •Alternative Storage Pattern - Save Deltas • Event vs Aggregate
- 63. Event: Something whichhas occurred in the system
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- 65. THIRDCHANNEL @svpember Event Sourcing •Alternative Storage Pattern - Save Deltas • Event vs Aggregate • Purely Additive
- 66. There is noDelete
- 67. THIRDCHANNEL @svpember Event Sourcing •Alternative Storage Pattern - Save Deltas • Event vs Aggregate • Purely Additive • It’s Old
- 70. THIRDCHANNEL @svpember Event Sourcing •Alternative Storage Pattern - Save Deltas • Event vs Aggregate • Purely Additive • It’s Old • Event Stream -> Transient Models
- 72. All Objects areTransient Derivatives of the Event Stream
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- 74. I’m sure you havesome doubts.
- 75. Wouldn’t it takeup a large amount of storage space?
- 77. Wouldn’t ES addoverhead?
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- 80. Try to avoid‘heavy’ persistence mechanisms
- 81. The toughest thing,though:
- 82. ES Can be difficultfor junior developers
- 83. THIRDCHANNEL @svpember So WhyWould I Want Event Sourcing?
- 84. THIRDCHANNEL @svpember So WhyES? • More than the Perfect Audit Log
- 85. Audit logs tellthe History Events tell the intent of History
- 87. Also, You’re now aTime Traveller
- 88. THIRDCHANNEL @svpember So WhyES? • More than the Perfect Audit Log • Only Structural Model That Does Not Lose Information
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- 90. THIRDCHANNEL @svpember So WhyES? • More than the Perfect Audit Log • Only Structural Model That Does Not Lose Information • Ideal for Business Analysis
- 91. Analysis of the Event Streamis a Projection
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- 93. THIRDCHANNEL @svpember Current Stateis Boring • Mine ALL ProductRemoved events • Find ALL ProductAdded events followed by RemovedEvents for same product within 5 minutes • Find Average Duration between ProductAdd and OrderPlaced
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- 95. Future Proof yourData!
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- 101. Businesses depend on TimeSeries Data
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- 109. Successful Commands Resultin new Events on the Aggregate
- 110. –Johnny Appleseed “Type aquote here.”
- 111. Loading a Querybuilds up Aggregates from the Events
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- 114. THIRDCHANNEL @svpember Tying ItAll Together
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- 116. –Johnny Appleseed “Type aquote here.”
- 117. The Event Streamis the Source of Truth.
- 118. Pre-Build Query Objectsfrom the Event Stream
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- 120. THIRDCHANNEL @svpember What havewe learned @ThirdChannel?
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- 122. There are fewavailable tools …
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- 124. THIRDCHANNEL @svpember Akka &Akka Persistance
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- 126. …and we usednone of them
- 127. –Johnny Appleseed “Type aquote here.”
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- 129. Commands & Queries immediatelyfelt like a perfect fit
- 130. …and make sureyou append your class names with ‘Command’ and ‘Query’
- 131. Query - basedViews are an efficiency gain
- 132. Query Read Modelsshould be able to be freely trashed and rebuilt
- 133. We’ve still notrun into Aggregate write contention
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- 136. You really don’tneed snapshots (at first)
- 137. Be Wary ofEditing an Event
- 138. Small Events >Large Events
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- 141. This next bitis important
- 142. Pure Event SourcingIs Not Always The Best Choice
- 143. Include a ‘dateEffective’ fieldon the Event table
- 144. Add Current-State, Indexed, Columnsto your Aggregates
- 145. And Make Manyof Them
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- 149. THIRDCHANNEL @svpember Image Credits •Mad Developers: Last Week Tonight • CQRS Diagram: http://udidahan.com/2009/12/09/clarified-cqrs/ • Happy Developers: http://www.businessinsider.com/programming-languages-in-highest-demand-2015-6 • Obama Thumbs up: http://amiloszportraits.com/barack-obama-thumbs-up-meme • Who am i?: http://www.catholicismusa.com/want-joy-seek-god-find-your-true-identity/ • Star Trek face palm: http://tvtropes.org/pmwiki/pmwiki.php/FacePalm/LiveActionTV • Sauron’s Eye: http://www.independent.co.uk/arts-entertainment/architecture/russian-orthodox-church-condemns- moscows-eye-of-sauron-art-installation-celebrating-the-hobbit-the-9915050.html • Grain of Salt: http://www.pxleyes.com/photography-picture/4c3004291f903/Grain-of-Salt.html • Obama, Nye, and Tyson: en.wikipedia.org/wiki/Selfie