The document provides an introduction to Cassandra presented by Nick Bailey. It discusses key Cassandra concepts like cluster architecture, data modeling using CQL, and best practices. Examples are provided to illustrate how to model time-series data and denormalize schemas to support different queries. Tools for testing Cassandra implementations like CCM and client drivers are also mentioned.

1. Introduction to Cassandra
Nick Bailey
@nickmbailey
Monday, October 28, 13

2. Who am I?
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3. What’s DataStax?
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4. On to the good stuff!
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5. Why Cassandra?
Cluster Architecture
Node Architecture
5
Data Modeling
Wrap up
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6. Why Cassandra?
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7. Time for buzz
words!
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Big Data!
NoSQL!
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8. Big Data
• Gartner: “...high-volume, high-velocity and
high-variety...”
• 2 sides of ‘big data’
•
•
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Analytics
Real-time
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9. NoSQL
• A terrible label
• Covers a wide range of DBs
•
•
•
•
•
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Cassandra
Redis
MongoDB
HBase
...
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10. Started by Facebook
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11. Dynamo (Amazon)
+
Big Table (Google)
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13. Cassandra is great for...
• Massive, linear scaling
(e.g. CERN hadron collider, Barracuda Networks)
• Extremely heavy writes
(e.g. BlueMountain Capital – financial tick data)
• High availability
(e.g. eBay, Eventbrite, Netflix, SoundCloud,
HeathCare Anytime, Comcast, GoDaddy, Sony
Entertainment Network)
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16. http://techblog.netflix.com/2012/07/lessons-netflix-learned-from-aws-storm.html
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17. One size does not fit all
Polyglot persistence
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18. More Resources
• PlanetCassandra.org
• Blog
• 5 minute interviews
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19. Cluster Architecture
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20. Data Distribution
0
75
25
50
Hash_Function(Partition Key) >> Token
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21. Replication
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22. Failure Modes
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23. Consistency Level
• Multiple options
•
•
•
•
•
ONE
QUORUM
ALL
LOCAL_QUORUM
...
• Can be specified per request
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24. Quorum
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25. Quorum
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26. Consistency
Write
CL: ONE
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27. Consistency
Read
CL: One
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28. Failure Types
• UnavailableException
•
Didn’t even try
•
Possible success or failure
• TimedOutException
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29. Multi DC
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30. Gossip
• Manages cluster state
•
•
Nodes up/down
Nodes joining/leaving
• Decentralized
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31. Snitch
• Responsible for determining cluster topology
• Tracks node responsiveness
• Simple, PropertyFile, Ec2Snitch, etc...
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32. Node Architecture
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33. Write Path
Write
Memtable
Memory
Disk
commit log
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SSTable
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34. Read Path
Read
Memtable
Memory
Disk
SSTable
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SSTable
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35. Data Modeling
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36. CQL
Cassandra Query Language
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37. Terminology
• Keyspace
• Table (Column Family)
• Row
• Column
• Partition Key
• Clustering Key (Optional)
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38. For Example:
CREATE KEYSPACE packagetracker WITH REPLICATION = { 'class' :
'SimpleStrategy', 'replication_factor' : 1 };
CREATE KEYSPACE packagetracker WITH REPLICATION = { 'class' :
'NetworkTopologyStrategy', 'dc1' : 2, 'dc2' : 2};
CREATE TABLE events (
package_id text,
status_timestamp timestamp,
location text,
notes text,
PRIMARY KEY (package_id, status_timestamp)
);
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39. Constructs
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40. Basic Data Types
• blob
• int
• text
• long
• uuid
• etc
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41. More Data Modeling Constructs
• Collections
•
map, set, list
• Time to live (TTL)
• Counters
• Secondary Indexes
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42. Approaching Data Modeling
• Model your queries, not your data
•
Optimize your data model for reads
• Don’t be afraid to denormalize
• You will get it wrong, iterate
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43. An Example:
User Logins
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44. The Query
What are the last 10 locations nickmbailey logged in from?
SELECT time, location FROM logins WHERE user = ‘nickmbailey’
ORDER BY time DESC LIMIT 10;
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45. The Query
What are the last 10 locations nickmbailey logged in from?
SELECT time, location FROM logins WHERE user = ‘nickmbailey’
ORDER BY time DESC LIMIT 10;
Partition Key
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46. The Query
What are the last 10 locations nickmbailey logged in from?
SELECT time, location FROM logins WHERE user = ‘nickmbailey’
ORDER BY time DESC LIMIT 10;
Clustering Key
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Partition Key
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47. The Query
What are the last 10 locations nickmbailey logged in from?
SELECT time, location FROM logins WHERE user = ‘nickmbailey’
ORDER BY time DESC LIMIT 10;
Clustering Key
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Partition Key
Additional Columns
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48. The Query
What are the last 10 locations nickmbailey logged in from?
SELECT time, location FROM logins WHERE user = ‘nickmbailey’
ORDER BY time DESC LIMIT 10;
Clustering Key
Partition Key
Additional Columns
CREATE COLUMN FAMILY logins (
user text,
time timestamp,
location text,
PRIMARY KEY (user, time));
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49. The Query
What are the last 10 locations nickmbailey logged in from?
SELECT time, location FROM logins WHERE user = ‘nickmbailey’
ORDER BY time DESC LIMIT 10;
CREATE COLUMN FAMILY logins (
user text,
time timestamp,
location text,
PRIMARY KEY (user, time));
Partition key
Primary key
User
Time
Location
nickmbailey
2013-07-19 09:22:18
Austin, Texas
nickmbailey
2013-07-19 14:49:27
Blacksburg, Virginia
jsmith
2013-07-20 07:59:34
Atlanta, Georgia
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50. Time-series data
• By far, the most common data model
• Event logs
• Metrics
• Sensor Data
• Etc
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51. Another Query
When was the last time nickmbailey logged in from San
Francisco, California?
SELECT time FROM logins WHERE user = ‘nickmbailey’ and
location=‘San Francisco, California’;
User
Time
Location
nickmbailey
2013-07-19 09:22:18
Austin, Texas
nickmbailey
2013-07-19 14:49:27
Blacksburg, Virginia
nickmbailey
2013-07-19 14:49:27
Austin, Texas
nickmbailey
2013-05-19 14:49:27
Austin, Texas
nickmbailey
2013-04-19 14:49:27
San Francisco, California
...
...
...
jsmith
2013-07-20 07:59:34
Atlanta, Georgia
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52. Another Query
When was the last time nickmbailey logged in from Austin,
Texas?
SELECT time FROM logins_by_location WHERE user = ‘nickmbailey’
and location=‘San Francisco, California’;
CREATE COLUMN FAMILY logins_by_location (
user text,
time timestamp,
location text,
PRIMARY KEY (user, location));
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53. Another Query
When was the last time nickmbailey logged in from Austin,
Texas?
SELECT time FROM logins_by_location WHERE user = ‘nickmbailey’
and location=‘San Francisco, California’;
CREATE COLUMN FAMILY logins_by_location (
user text,
time timestamp,
location text,
PRIMARY KEY (user, location));
User
Location
Time
nickmbailey
Austin, Texas
2013-07-19 09:22:18
nickmbailey
Blacksburg, Virginia
2013-07-19 14:49:27
nickmbailey
San Francisco, California
2013-07-19 14:49:27
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54. Denormalize
• Create materialized views of the same data to
support different queries
• Storage space is cheap, Cassandra is fast
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55. Debugging your data model
cqlsh> tracing on;
Now tracing requests.
cqlsh:foo> INSERT INTO test (a, b) VALUES (1, 'example');
Tracing session: 4ad36250-1eb4-11e2-0000-fe8ebeead9f9
activity
| timestamp
| source
| source_elapsed
-------------------------------------+--------------+-----------+---------------execute_cql3_query | 00:02:37,015 | 127.0.0.1 |
0
Parsing statement | 00:02:37,015 | 127.0.0.1 |
81
Preparing statement | 00:02:37,015 | 127.0.0.1 |
273
Determining replicas for mutation | 00:02:37,015 | 127.0.0.1 |
540
Sending message to /127.0.0.2 | 00:02:37,015 | 127.0.0.1 |
779
Messsage received from /127.0.0.1
Applying mutation
Acquiring switchLock
Appending to commitlog
Adding to memtable
Enqueuing response to /127.0.0.1
Sending message to /127.0.0.1
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56. A note on Transactions
• In general, you want to construct your data
model around them
• The latest version of Cassandra has ‘Compare
and swap’
•
•
•
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An implementation of Paxos
...IF NOT EXISTS;
...IF column1 = ‘value’;
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57. Try it out
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58. CCM
• CCM - Cassandra Cluster Manager
•
https://github.com/pcmanus/ccm
•
•
•
ccm create test -v 2.0.1
ccm populate -n 3
ccm start
• Warning: not lightweight
• Example:
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59. Clients
• Cqlsh
•
Bundled with Cassandra
•
•
•
•
java: https://github.com/datastax/java-driver
python: https://github.com/datastax/python-driver
.net: https://github.com/datastax/csharp-driver
and more: http://www.datastax.com/download/
clientdrivers
• Drivers
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60. Get Help
• IRC: #cassandra on freenode
• Mailing Lists
• Stack Overflow
• DataStax Docs
•
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http://www.datastax.com/docs
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61. Questions?
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62. Monday, October 28, 13