My talk from http://wdcnz.com 2012. I took a brief look at Cassandra and then stepped through building a twitter clone. Very rough code is at https://github.com/amorton/wdcnz-2012-site

1. HELLO @WORLD #CASSANDRA
APACHE CASSANDRA IN ACTION
WDCNZ 2012
Aaron Morton, Apache Cassandra Committer
@aaronmorton
www.thelastpickle.com
Licensed under a Creative Commons Attribution-NonCommercial 3.0 New Zealand License

2. The Code is at...
github.com/amorton/wdcnz-2012-site

3. Cassandra?

4. Cassandra?
Started at
Facebook.

5. Cassandra?
Top Level Apache
project since 2010.

6. Used by...
Netflix, Twitter,
Reddit, Rackspace...

7. Commercial support by...
Data Stax, Acunu,
PalominoDB,
Impetus...

8. Why Cassandra?
Scale

9. Why Cassandra?
Operations

10. Why Cassandra?
Data Model

11. Cluster

12. Store ‘foo’ key with Replication Factor 3.
Node 1 - 'foo'
Node 4 Node 2 - 'foo'
Node 3 - 'foo'

13. Consistent Hashing...
Evenly map keys to
nodes.

14. Consistent Hashing...
Minimise key
movements when nodes
join or leave.

15. Partitioner...
RandomPartitioner
transforms Keys to Tokens
using MD5.
(Default Partitioner, there are others.)

16. Keys and Tokens?
key 'fop' 'foo'
token 0 10 90 99

17. Token Ring.
99 0
'foo' 'fop'
token: 90 token: 10

18. Token Ranges.
Node 1
token: 0
76-0 1-25
Node 4 Node 2
token: 75 token: 25
Node 3
token: 50

19. Locate Token Range.
Node 1
token: 0
'foo'
token: 90
Node 4 Node 2
token: 75 token: 25
Node 3
token: 50

20. Replication Strategy selects
Replication Factor number of
nodes for a row.

21. SimpleStrategy with RF 3.
Node 1
token: 0
'foo'
token: 90
Node 4 Node 2
token: 75 token: 25
Node 3
token: 50

22. Clients connect to
any node in the
cluster.

23. The Client and the Coordinator.
Node 1
token: 0
'foo'
token: 90
Node 4 Node 2
token: 75 token: 25
Node 3
Client
token: 50

24. Client specified
Consistency Level.

25. Consistency Level...
Any*, One, Two,
Three,

26. Consistency Level...
QUORUM,
LOCAL_QUORUM,
EACH_QUOURM*

27. QUOURM at Replication Factor...
Replication
2 or 3 4 or 5 6 or 7
Factor
QUOURM 2 3 4

28. Node Down.
Node 1
token: 0
'foo'
token: 90
Node 4 Node 2
token: 75 token: 25
Node 3
Client
token: 50

29. Write ‘foo’ at QUOURM with Hinted Handoff.
Node 1
'foo'
'foo'
token: 90
Node 4 Node 2
'foo' for #3 'foo'
Node 3
Client

30. Read ‘foo’ at QUOURM.
Node 1
'foo'
'foo'
token: 90
Node 4 Node 2
'foo'
Node 3
Client

31. Consistency Level
nodes must agree.

32. Column Timestamps
used to resolve
differences.

33. Consistent read for ‘foo’ at QUOURM.
Node 1 Node 1
cromulent
cromulent
Node 4 Node 2 Node 4 Node 2
embiggins cromulent
cromulent
Client Client
Node 3 Node 3

34. R +W > N
(#Read Nodes + #Write Nodes > Replication Factor)

35. Data Model

36. Data Model so far.
Row Key: Column Column Column
(Incomplete.)

37. Data Model.
Keyspace
Column Family Column Family Column Family
Column Column Column
Row Key: Column Column Column
Column Column Column
(Excludes Super Columns.)

38. Data Model...
Keyspace
Column Family
Column: name, value, timestamp
Row Key: Column: name, value, timestamp
Column: name, value, timestamp
(Also TTL and Tombstone Columns.)

39. Code

40. Tweet Storage...
CF / User User User Global
User Tweet
Row Key Tweets Timeline Metrics Timeline
user_name ✓ ✓ ✓ ✓
tweet_id ✓

41. Followers Storage...
CF / Ordered
Relationships TweetDelivery
Row Key Relationships
(user_name,
rel_type) ✓ ✓
tweet_id ✓

42. Data Driven
Wellington
(It’s a meet-up on MeetUp.Com)

43. Aaron Morton
@aaronmorton
www.thelastpickle.com
Licensed under a Creative Commons Attribution-NonCommercial 3.0 New Zealand License