Event sourcing stores all state as a sequence of events and only stores facts rather than the current application state. It focuses on designing the domain model strategically first before considering data storage or other implementation details. Event sourcing is more complex than traditional approaches but can provide benefits for certain domains by making it easier to understand how the application state evolved over time.

1. Event Sourcing
Greg Young

5. Event Sourcing says all
state is transient and you
only store facts.

6. Purchase Order
Line Items (n)
Shipping Information

7. Cart
Created
3 Items
Added
Shipping
Informati
on Added

9. Cart
Created
3 Items
Added
1Item
Removed
Shipping
Informati
on Added

11. 7
6
5
4
3
2
1

12. 6
5
snap
4
3
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1

14. I can’t query a series
of events

15. Focus on strategic design first.

16. Focus on strategic design first.

17. There is no “Best”
storage

18. Focus on strategic design first.

19. Id ParentId Data
1 0 Parent
Focus on strategic design first.
2 1 Child1
3 1 Child2

20. Id ParentId0 ParentId1 ParentId2 ParentId3 ParentId4 Data
Focus on strategic design first.
1 0 0 0 0 0 Parent
2 1 0 0 0 0 Child1
3 1 2 0 0 0 Child2

21. Wrong models cause
accidental complexity

22. Domain
Client
OLAP
GraphDb
StreamProcessing
Events
Hibernate

23. Event Sourced Systems
need a service bus

24. Domain
Client
Bus
OLAP
GraphDb
StreamProcessing
publish
3nf
Hibernate

25. Domain
Client
Bus
OLAP
GraphDb
StreamProcessing
publish
3nf
Hibernate

26. Domain
Client
Bus
OLAP
GraphDb
StreamProcessing
publish
3nf
Hibernate
New Model?

27. Domain
Client
OLAP
GraphDb
StreamProcessing
Events
Hibernate

28. Domain
Client
OLAP
GraphDb
StreamProcessing
Events
Hibernate
New Model?

29. Event Sourcing is
more complex!

30. What big companies are
using Event Sourcing?
Because obviously we make our decisions this way!

31. Event Sourced
systems must be slow

32. Event Sourced systems
must be object oriented

33. What is the “bestest”
Event Sourcing
framework ever?

34. But what about all my
data with Event Sourcing
it must be huge!
If it fits on a micro-SD its not big data.

35. CQRS is just a
teaching pattern!

36. Event Sourced
systems must be slow

37. Event Sourced systems
must be object oriented

38. But what about all my
data with Event Sourcing
it must be huge!

39. Event Sourcing isn’t
“enterprisey”

40. Event Sourcing isn’t
“enterprisey”
THANKS!

41. No really Thanks!