Cassandra stores data differently than traditional RDBMS’s. It is these differences that allow for improvements in performance, availability and scalability. Aaron Morton, DataStax MVP for Apache Cassandra will present the basics of the data model and outline the differences clearly. This webinar is 101 level and is suitable for people who are coming from a relational background and just starting to get into Apache Cassandra.

1. DATASTAX C*OLLEGE CREDIT:
DATA MODELLING FOR
APACHE CASSANDRA
Aaron Morton
Apache Cassandra Committer, Data Stax MVP for Apache Cassandra
@aaronmorton
www.thelastpickle.com
Licensed under a Creative Commons Attribution-NonCommercial 3.0 New Zealand License

2. General Guidelines
API Choice
Example

3. Cassandra is good at
reading data from a row in the
order it is stored.

4. Typically an efficient data model will
denormalize data and use the
storage engine order.

5. To create a good data model
understand the queries your
application requires.

6. General Guidelines
API Choice
Example

7. Multiple API’s?
initially only a Thrift / RPC
API, used by language specific
clients.

8. Multiple API’s...
Cassandra Query Language
(CQL) started as a higher
level, declarative alternative.

9. Multiple API’s...
CQL 3 brings many changes.
Currently in Beta in
Cassandra v1.1

10. CQL 3 uses
a Table Orientated, Schema
Driven, Data Model.
(I said it had many changes.)

11. General Guidelines
API Choice
Example

12. Twitter Clone
Previously done with Thrift at WDCNZ
“Hello @World #Cassandra - Apache
Cassandra in action”
http://vimeo.com/49762233

13. Twitter clone...
using CQL 3 via the cqlsh
tool.
bin/cqlsh -3

14. Queries?
* Post Tweet to Followers
* Get Tweet by ID
* List Tweets by User
* List Tweets in User Timeline
* List Followers

15. Keyspace is
a namespace container.

16. Our Keyspace
CREATE KEYSPACE
cass_college
WITH
strategy_class = 'NetworkTopologyStrategy'
AND
strategy_options:datacenter1 = 1;

17. Table is
a sparse collection of well
known, ordered columns.

18. First Table
CREATE TABLE User
(
user_name text,
password text,
real_name text,
PRIMARY KEY (user_name)
);

19. Some users...
cqlsh:cass_college> INSERT INTO User
... (user_name, password, real_name)
... VALUES
... ('fred', 'sekr8t', 'Mr Foo');
cqlsh:cass_college> select * from User;
user_name | password | real_name
-----------+----------+-----------
fred | sekr8t | Mr Foo

20. Some users...
cqlsh:cass_college> INSERT INTO User
... (user_name, password)
... VALUES
... ('bob', 'pwd');
cqlsh:cass_college> select * from User where user_name =
'bob';
user_name | password | real_name
-----------+----------+-----------
bob | pwd | null

21. Data Model (so far)
User

22. Data Model (so far)
CF /
User
Value
user_name Primary Key

23. Tweet Table
CREATE TABLE Tweet
(
tweet_id bigint,
body text,
user_name text,
timestamp timestamp,
PRIMARY KEY (tweet_id)
);

24. Tweet Table...
cqlsh:cass_college> INSERT INTO Tweet
... (tweet_id, body, user_name, timestamp)
... VALUES
... (1, 'The Tweet','fred',1352150816917);
cqlsh:cass_college> select * from Tweet where tweet_id = 1;
tweet_id | body | timestamp | user_name
----------+-----------+--------------------------+-----------
1 | The Tweet | 2012-11-06 10:26:56+1300 | fred

25. Data Model (so far)
CF /
User Tweet
Value
user_name Primary Key Field
tweet_id Primary Key

26. UserTweets Table
CREATE TABLE UserTweets
(
tweet_id bigint,
user_name text,
body text,
timestamp timestamp,
PRIMARY KEY (user_name, tweet_id)
);

27. UserTweets Table...
cqlsh:cass_college> INSERT INTO UserTweets
... (tweet_id, body, user_name, timestamp)
... VALUES
... (1, 'The Tweet','fred',1352150816917);
cqlsh:cass_college> select * from UserTweets where
user_name='fred';
user_name | tweet_id | body | timestamp
-----------+----------+-----------+--------------------------
fred | 1 | The Tweet | 2012-11-06 10:26:56+1300

28. UserTweets Table...
cqlsh:cass_college> select * from UserTweets where
user_name='fred' and tweet_id=1;
user_name | tweet_id | body | timestamp
-----------+----------+-----------+--------------------------
fred | 1 | The Tweet | 2012-11-06 10:26:56+1300

29. UserTweets Table...
cqlsh:cass_college> INSERT INTO UserTweets
... (tweet_id, body, user_name, timestamp)
... VALUES
... (2, 'Second Tweet', 'fred', 1352150816918);
cqlsh:cass_college> select * from UserTweets where user_name = 'fred';
user_name | tweet_id | body | timestamp
-----------+----------+--------------+--------------------------
fred | 1 | The Tweet | 2012-11-06 10:26:56+1300
fred | 2 | Second Tweet | 2012-11-06 10:26:56+1300

30. UserTweets Table...
cqlsh:cass_college> select * from UserTweets where user_name = 'fred' order by
tweet_id desc;
user_name | tweet_id | body | timestamp
-----------+----------+--------------+--------------------------
fred | 2 | Second Tweet | 2012-11-06 10:26:56+1300
fred | 1 | The Tweet | 2012-11-06 10:26:56+1300

31. UserTimeline
CREATE TABLE UserTimeline
(
tweet_id bigint,
user_name text,
body text,
timestamp timestamp,
PRIMARY KEY (user_name, tweet_id)
);

32. Data Model (so far)
CF / User User
User Tweet
Value Tweets Timeline
user_name Primary Key Field Primary Key Primary Key
Primary Key Primary Key
tweet_id Primary Key
Component Component

33. UserMetrics Table
CREATE TABLE UserMetrics
(
user_name text,
tweets counter,
followers counter,
following counter,
PRIMARY KEY (user_name)
);

34. UserMetrics Table...
cqlsh:cass_college> UPDATE
... UserMetrics
... SET
... tweets = tweets + 1
... WHERE
... user_name = 'fred';
cqlsh:cass_college> select * from UserMetrics where user_name
= 'fred';
user_name | followers | following | tweets
-----------+-----------+-----------+--------
fred | null | null | 1

35. Data Model (so far)
CF / User User
User Tweet User Metrics
Value Tweets Timeline
Primary Primary Primary Primary
user_name Field
Key Key Key Key
Primary Primary Key Primary Key
tweet_id
Key Component Component

36. Relationships
CREATE TABLE Followers
(
user_name text,
follower text,
timestamp timestamp,
PRIMARY KEY (user_name, follower)
);
CREATE TABLE Following
(
user_name text,
following text,
timestamp timestamp,
PRIMARY KEY (user_name, following)
);

37. Relationships
INSERT INTO
Following
(user_name, following, timestamp)
VALUES
('bob', 'fred', 1352247749161);
INSERT INTO
Followers
(user_name, follower, timestamp)
VALUES
('fred', 'bob', 1352247749161);

38. Relationships
cqlsh:cass_college> select * from Following;
user_name | following | timestamp
-----------+-----------+--------------------------
bob | fred | 2012-11-07 13:22:29+1300
cqlsh:cass_college> select * from Followers;
user_name | follower | timestamp
-----------+----------+--------------------------
fred | bob | 2012-11-07 13:22:29+1300

39. Data Model
CF / User User User Follows
User Tweet
Value Tweets Timeline Metrics Followers
Primary
Primary Primary Primary Primary
user_name Field Key
Key Key Key Key
Field
Primary Primary Key Primary Key
tweet_id
Key Component Component

40. Thanks.

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