Talk about Apache Cassandra at the DomCode meetup in Utrecht on March 31 2015.

1. Storing Data the Cassandra Way
Freek van Polen
“Simplicity is the ultimate sophistication.”
-Leonardo Da Vinci

2. About Me
● Cognitive Artificial Intelligence @ UU
● Almende:
– Researcher, self-organization, wireless sensor
networks
● Sense:
– First employee, developer, backend, team leader

3. Goal of this Talk
● Not to tell you to use Cassandra for everything

4. Goal of this Talk
● Not to tell you to use Cassandra for everything
● Not to go into all gory details of Cassandra

5. Goal of this Talk
● Not to tell you to use Cassandra for everything
● Not to go into all gory details of Cassandra
● Not to show off my drawing skills

6. Goal of this Talk
● Introduce some database theory

7. Goal of this Talk
● Introduce some database theory
● Make you enthusiastic about Cassandra

8. Goal of this Talk
● Introduce some database theory
● Make you enthusiastic about Cassandra
Use the right tool for the job!

9. SQL vs NoSQL

10. Non relational data
● documents
● graphs
● key-value
● wide-row
{
“meetup”: “DomCode”,
“name”: “Monthly Meetup March”,
“date”: “31­03­2015”,
“organizers”: [
“Ross”,
“Lucas”
],
“location”: “Infi”,
“talks”: [
{
“speaker”: “Arian”,
“topic”: “functional js”
},
{
“speaker”: “Freek”,
“topic”: “cassandra”,
“length”: 45
}
]
}

11. Non relational data
● documents
● graphs
● key-value
● wide-row

12. Non relational data
● documents
● graphs
● key-value
● wide-row
“6573672017456”: “tom”
“9810919283853”: “mary”
“1129823948673”: “jane”
“9827712003003”: “dani”

13. Non relational data
● documents
● graphs
● key-value
● wide-row
Stock 1: [+3.23, +5.02, ­2.45, ­34.12, ­12.65, +0.43]
Stock 2: [+5.34, +6.34, +9.12, +0.53]
Stock 3: [­3.21, ­5.32, ­8.12, ­0.53, ­0.12, +0.43, +0.76, +2.55]

14. Scalability
Database [A-Z]

15. Scalability
Database [A-Z]

16. Scalability: replication
Database [A-Z]
Copy of Database [A-Z]

17. Scalability: sharding
Database [A-M]
Database [N-Z]

18. Scalability: combined
(oh the horror)
Database [A-M] Copy of Database [A-M]
Database [N-Z] Copy of Database [N-Z]

19. Coordinator
Scalability: combined
(oh the horror)
Database [A-M] Copy of Database [A-M]
Database [N-Z] Copy of Database [N-Z]

20. CAP theorem

21. CAP theorem
RDBMS

22. ACID & BASE
● Atomicity
● Consistency
● Isolation
● Durability
● Basically
● Available
● Soft-state
● Eventual consistency

23. Cassandra o/

24. Cassandra Cluster
● All nodes are equal
● All nodes can process any request
● Throughput and storage space scales linearly
● Graceful degradation

25. Cassandra: Gossip
5
37
1
8 2
46

26. Cassandra: Gossip
5
37
1
8 2
46

27. Cassandra: Replication
5
37
1
8 2
46
Token Ring

28. Cassandra: Replication
5
37
1
8 2
46
[A - D]
[E - H]
[I - K]
[L - N][O - Q]
[R - T]
[U - W]
[X - Z]

29. Cassandra: Replication
5
37
1
8 2
46
[A - D]
[E - H]
[I - K]
[L - N][O - Q]
[R - T]
[U - W]
[X - Z] replication = 3

30. Cassandra: Request Processing
5
37
1
8 2
46
K: 12-24?

31. Cassandra: Request Processing
5
37
1
8 2
46
K: 12-24? K: 12-24?

32. Cassandra: Request Processing
5
37
1
8 2
46
K: 12-24!
K: 12-24!

33. Cassandra: Request Processing
5
37
1
8 2
46
K: 12-24!

34. Cassandra: Request Processing
5
37
1
8 2
46
K:22 = “tom”

35. Cassandra: Request Processing
5
37
1
8 2
46
K:22 = “tom” K:22 = “tom”

36. Cassandra: Request Processing
5
37
1
8 2
46
Got it!
Great success!

37. Cassandra: Request Processing
5
37
1
8 2
46
K:22 = “tom”
K:22 = “tom”
K:22 = “jerry”

38. Cassandra: Request Processing
5
37
1
8 2
46
K:22 = “tom”
K:22 = “tom”
K:22 = “jerry”
K:22 = “tom”

39. Cassandra: Request Processing
5
37
1
8 2
46
K:22 = “tom”
K:22 = “tom”
K:22 = “tom”

40. Cassandra: Tunable Consistency
● Consistency.ANY
● Consistency.ONE
● Consistency.QOURUM
● Consistency.ALL

41. Cassandra: Data Model
CREATE TABLE transactions (
account_id string,
date timestamp,
amount float,
other_account string,
PRIMARY KEY (account_id, date)
);

42. Cassandra: Data Model
CREATE TABLE transactions (
account_id string,
date timestamp,
amount float,
other_account string,
PRIMARY KEY (account_id, date)
);
29-03-2015
15:23:45
29-03-2015
16:56:21
30-03-2015
04:00:00
NLRABOxxx amount: -143.90
other: NLINGxxx
amount: -29.30
other: NLABNxxx
amount: +2000.00
other: NLASNxxx

43. Cassandra Data Model
● Primary Key #1:
– Row key
– Unit of partitioning
● Primary Key #2:
– Column key
– Order within row
– Order is preserved on disk!

44. Distributed Concurrent Writes
from: https://aphyr.com/posts/294-call-me-maybe-cassandra

45. Distributed Concurrent Writes
● Last write wins
● Paxos
● Treat data as
immutable
from: https://aphyr.com/posts/294-call-me-maybe-cassandra

46. Distributed Concurrent Writes
● Cassandra trades
consistency for
availability, partition
tolerance, and super
easy administration...
● This is not for all use
cases
from: https://aphyr.com/posts/294-call-me-maybe-cassandra

47. THE use case: time series data
CREATE TABLE sensor_data (
sensor_id text,
time timestamp,
value text,
PRIMARY KEY (sensor_id, time)
);

48. Thanks!

49. Cassandra?