Cassandra is a NoSQL database designed for scalability and high availability without compromising performance. It distributes data across nodes and datacenters for redundancy and fault tolerance. Cassandra uses a decentralized architecture and dynamic replication to balance requests and allow incremental growth without reconfiguring the system. It provides tunable consistency options and supports column-oriented data storage for flexibility and efficient queries.

1. Cassandra
Jonathan Ellis
@spyced
jbellis@riptano.com
Tuesday, April 20, 2010

2. Tuesday, April 20, 2010

3. Tuesday, April 20, 2010

4. Tuesday, April 20, 2010

5. “NoSQL”
Performance Reliability
Scaling B&D
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6. Performance
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Each Cassandra node manages its storage locally. Not limited by obsolete systems, and not
slowed by layering on top of a DFS.

7. b-trees
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read-before-write
index in ram
random i/o

8. Memtable / SSTable
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9. Durable
• Write to commitlog
• fsync is cheap since it’s append-only
• Write to memtable
• [amortized] flush memtable to sstable
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Cassandra is one of the few NoSQL systems that is suitable for use when data loss is
unacceptable.

10. SSTable format, briefly
<row data 0>
<key 127>
<row data 1>
<key 255>
...
...
<row data 127>
...
<row data 255>
...
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11. Scaling
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How managing our own data helps scaling

12. Scaling
• Facebook: grew from less than 80 machines
to 150+
• SimpleGEO: from 20 EC2 Large instances
to 50+
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13. How it works
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14. W A
T
L
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15. W A
F
T
L
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16. W A
(A-F] F
T
(F-L]
L
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17. Key “C”
W A
F
T
L
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18. Reliability
• No single points of failure
• Multiple datacenters
• Monitorable
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19. Design
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20. The opposite of heroes
• “If your software wakes people up at 4 AM
to fix it, you’re doing it wrong.”
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21. W A
T
L
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Every node is equal

22. Y
Key “C”
A
W
U
F
T
L
P
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Always at least one copy in each datacenter
Alternate datacenters on the ring

23. Monitorable
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24. Events
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25. JMX
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26. Bondage & Discipline
• Twitter: “Fifteen months ago, it took two
weeks to perform ALTER TABLE on the
statuses [tweets] table.”
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27. ColumnFamilies
Columns
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28. SuperColumns
SuperColumns
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29. Twissandra
User = {
'a4a70900-24e1-11df-8924-001ff3591711': {
'id': 'a4a70900-24e1-11df-8924-001ff3591711',
'username': 'ericflo',
'password': '****',
},
}
Followers = {
'a4a70900-24e1-11df-8924-001ff3591711': {
# friend id: timestamp of when the followership was added
'10cf667c-24e2-11df-8924-001ff3591711': '1267413962580791',
'343d5db2-24e2-11df-8924-001ff3591711': '1267413990076949',
'3f22b5f6-24e2-11df-8924-001ff3591711': '1267414008133277',
},
}
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30. Tweet = {
'7561a442-24e2-11df-8924-001ff3591711': {
'id': '89da3178-24e2-11df-8924-001ff3591711',
'user_id': 'a4a70900-24e1-11df-8924-001ff3591711',
'body': 'Trying out Twissandra. This is awesome!',
'_ts': '1267414173047880',
},
}
Timeline = {
'a4a70900-24e1-11df-8924-001ff3591711': {
# timestamp of tweet: tweet id
1267414247561777: '7561a442-24e2-11df-8924-001ff3591711',
1267414277402340: 'f0c8d718-24e2-11df-8924-001ff3591711',
1267414305866969: 'f9e6d804-24e2-11df-8924-001ff3591711',
1267414319522925: '02ccb5ec-24e3-11df-8924-001ff3591711',
},
}
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31. Tuesday, April 20, 2010

32. Denormalize
Userline = {
'a4a70900-24e1-11df-8924-001ff3591711': {
# timestamp of tweet: tweet id
1267414247561777: '7561a442-24e2-11df-8924-001ff3591711',
1267414277402340: 'f0c8d718-24e2-11df-8924-001ff3591711',
1267414305866969: 'f9e6d804-24e2-11df-8924-001ff3591711',
1267414319522925: '02ccb5ec-24e3-11df-8924-001ff3591711',
},
}
Tuesday, April 20, 2010

33. A note on UUIDs
• TimeUUID = Version 1 UUID
• LexicalUUID = any UUID
• usually version 4
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UUIDs are better than timestamps

34. Questions
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