Event Sourcing is powerful way to think about domain objects and transaction processing. Rather than persisting current state, event sourcing instead writes an immutable log of deltas to the db. Application state is derived, at any point in the past, simply by replaying the event history. Event sourcing is a deceptively radical idea which challenges our contemporary notions about transaction processing, while also being a mature pattern with a long history, used in databases, IoT and finance.

1. Event Sourcing
THE BEST, UBIQUITOUS PATTERN
YOU’VE NEVER HEARD OF
@blimpyacht

5. 5

7. User: A
Balance:
427
User: B
Balance:
550

8. User: A
Balance:
427
User: B
Balance:
550

9. User: A
Balance:
427
User: B
Balance:
550
+5-5

10. Event Sourcing
State

11. +4
-2
+5
+7
-4
+9
-3
-6
+2
+1
+1
-5 t(12) = 9
Event Sourcing

12. +4
-2
+5
+7
-4
+9
-3
-6
+2
+1
+1
-5
t(5) = 10
Event Sourcing

13. +4
-2
+5
+7
-4
+9
-3
-6
+2
+1
+1
-5
t(9) = 12
Event Sourcing

14. +4
-2
+5
+7
-4
+9
-3
-6
+2
+1
+1
-5
Event Sourcing
a = f ’(x)

15. +4
-2
+5
+7
-4
+9
-3
-6
+2
+1
+1
-5
Event Sourcing
+5
-4
+5

17. Res Gestae Divi Augusti

22. 2ndaryPrimary

23. 2ndaryPrimary

24. 2ndaryPrimary

25. +4
-2
+5
+7
-4
+9
-3
-6
+2
+1
+1
-5
Event Sourcing

26. +4
-2
+5
+7
-4
+9
-3
-6
+2
+1
+1
-5
t(4) = 14
Event Sourcing
t(8) = 10
t(12) = 9

27. +4
-2
+5
+7
-4
+9
-3
-6
+2
+1
+1
-5
t(4) = 14
Event Sourcing
t(8) = 10
t(12) = 9
t’(4) = -2
t’(8) = -17
t’(12) = -22

29. {
_id: {
ts: 1213084687000,
taxi: "abboip"
},
loc: {
geometry: [
-122.39488,
37.75134
]
},
fare: 0,
ts: ISODate("2008-06-10T07:58:07Z")
}

31. {
_id: ObjectId("56a4215a46778b69e08ff8ff"),
taxi: "abboip",
start: ISODate("2008-05-17T14:51:10Z"),
route: {
type: "LineString",
coordinates: [
[ -122.39724, 37.74977 ],
[ -122.40619, 37.74896 ],
[ -122.41335, 37.74831 ],
[ -122.414, 37.75157 ],
[ -122.41438, 37.75552 ]
]
},
end: ISODate("2008-05-17T14:55:58Z")
}

33. Data Modeling Domain Events
Domain Objects

35. Accounts
Payable

36. Accounts
Payable
Accounts
Receivable

37. Accounts
Payable
Accounts
Receivable
Journal

38. Accounts
Payable
Accounts
Receivable
Journal
Ledger

39. Command Query
Responsibility
Segregation

40. CQRS

41. CRUD vs. CQRS
CRUD

42. CRUD vs. CQRS
WRITE
READ

43. CRUD vs. CQRS

44. CRUD equals CQRS

45. WRITE
READ
READ
CRUD vs. CQRS

46. WRITE
READ
Variant Read Models: VIEWS
READ
READ
READ
READ

47. WRITE
READ
Primary
READ
CRUD vs. CQRS

48. CRUD vs. CQRS
WRITE
READ
READ
Primary
2ndary
2ndary

49. Where it Gets Tricky

50. CRUD vs. CQRS
WRITE
READ
READ
Primary
2ndary
2ndary

51. CRUD vs. CQRS
WRITE
READ
READ
Primary
2ndary
2ndary

52. Consistent Replay
+4
-2
+5
+7
-4
+9
-3
-6
+2
+1
+1
-5
t(5) = 10 Exchange Rate
Server
10 / 0.88 = 8.82€

53. Consistent Replay
+4
-2
+5
+7
-4
+9
-3
-6
+2
+1
+1
-5
t(5) = 10 Exchange Rate
Server
10 / 0.87 = 8.70€

54. +4
-2
+5
+7
-4
+9
-3
-6
+2
+1
+1
-5
0.88
Exchange Rate
Server
Consistent Replay

55. Where it Gets Trickier Still

60. External Updates
+4
-2
+5
+7
-4
+9
-3
-6
+2
+1
+1
-5
Notification
Subscriber

63. External Updates
+4
-2
+5
+7
-4
+9
-3
-6
+2
+1
+1
-5
Notification
Subscriber

64. Gaining Insight