This presentation will describe the fundamentals of Event Sourcing, how every action is stored as an event and how every state of the application can be reconstructed. Cristian Iliescu, Software Engineer @ Endava: https://www.linkedin.com/in/cristian-teodor-iliescu-31b16669?trk=hp-identity-photo https://twitter.com/ctiliescu https://www.meetup.com/members/198317888/

1. EVENT SOURCING
Cristian Iliescu ( )cristian.iliescu@endava.com

2. “We are the sum total of our experiences. Those experiences
– be they positive or negative – make us the person we are,
at any given point in our lives. And, like a flowing river, those
same experiences, and those yet to come, continue to
influence and reshape the person we are, and the person we
become. None of us are the same as we were yesterday, nor
will be tomorrow.”

3. WHAT IS AN EVENT?

4. An event is a notable thing
It happened in the past => is immutable
Involves one “producer” and one or many “consumers”

6. LET'S CHANGE THE
PERSPECTIVE

7. ACCOUNT EXAMPLE
Open an account
Receive some money
Make a payment
Check balance
Make another payment

8. MYSQL APPROACH
Action MySQL action
Action MySQL action
create account table Create
create account Insert
receive money Read + Update
make payment Read + Update
check balance Read
make payment Read + Update

9. ES APPROACH
Action NoSQL action
Action NoSQL action
create account Create
receive money Create
make payment Create
check balance Read
make payment Create

10. EVENT SOURCING
PRINCIPLES

11. Representing objects as a sequence of events
Never modify, always go forward
CRUD => CR

12. HOW IT WORKS ?

13. Captures every change of the application in an event
Organises all the events in order
Combines all events in the right order to obtain the state
from a specific moment

14. WHY EVENT
SOURCING?

15. Storage Ignorance
Flexibility
Improved performance
Simplify Developer's Life

16. STORAGE IGNORANCE & FLEXIBILITY
All data are stored as events
No more tables and complex relationships
Save and execute

17. IMPROVED PERFORMANCE
Events can be published as soon as they happen
No blocking operations
Events can be processed in parallel
Events can be multiplexed to multiple subscribers
Keep read models directly in memory

18. SIMPLIFY DEVELOPER'S LIFE
Simplifies deployment and maintenance
No data is ever lost
Reduces expenses on both the hardware and so ware
Fits very well with new technologies: Cloud Computing,
Big Data processing

19. OPTIMIZATION

20. OBJECTS WITH COMPLEX LIFETIMES

21. CQRS

22. DOWNSIDES

23. Extra storage costs
Few frameworks to support event sourcing
Lack of information and guidance

24. CONCLUSIONS

25. Event Sourcing doesn't lose information
=> it offers the possibility to create a wide variety of
reports
Compatible with non relational database

26. Q&A