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Tuesday, April 20, 2010
Tuesday, April 20, 2010
Tuesday, April 20, 2010
“NoSQL”
Reliability
Scaling B&D
Performance
Tuesday, April 20, 2010
Performance
Tuesday, April 20, 2010
Each Cassandra node manages its storage locally. Not limited by obsolete systems, and not slowed by layering on top of a DFS.
b-trees
Tuesday, April 20, 2010
read-before-writeindex in ramrandom i/o
Memtable / SSTable
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Durable
• Write to commitlog
• fsync is cheap since it’s append-only
• Write to memtable
• [amortized] flush memtable to sstable
Tuesday, April 20, 2010
Cassandra is one of the few NoSQL systems that is suitable for use when data loss is unacceptable.
SSTable format, briefly
<row data 0><row data 1>
...<row data 127>
...<row data 255>
...
<key 127><key 255>
...
Tuesday, April 20, 2010
Scaling
Tuesday, April 20, 2010
How managing our own data helps scaling
Scaling
• Facebook: grew from less than 80 machines to 150+
• SimpleGEO: from 20 EC2 Large instances to 50+
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How it works
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A
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A
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F
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A
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F(A-F]
(F-L]
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A
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Key “C”
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Reliability
• No single points of failure
• Multiple datacenters
• Monitorable
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Design
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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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A
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Every node is equal
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P
Y Key “C”
U
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Always at least one copy in each datacenterAlternate datacenters on the ring
Monitorable
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Events
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JMX
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Bondage & Discipline
• Twitter: “Fifteen months ago, it took two weeks to perform ALTER TABLE on the statuses [tweets] table.”
Tuesday, April 20, 2010
ColumnFamiliesColumns
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SuperColumns
SuperColumns
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TwissandraUser = { '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', },}
Tuesday, April 20, 2010
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', },}
Tuesday, April 20, 2010
Tuesday, April 20, 2010
DenormalizeUserline = { '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
A note on UUIDs
• TimeUUID = Version 1 UUID
• LexicalUUID = any UUID
• usually version 4
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UUIDs are better than timestamps
Questions
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