C*ollege Credit: Data Modeling for Apache Cassandra

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

General Guidelines
API Choice
Example

Cassandra is good at

reading data from a row in the
order it is stored.

Typically an efﬁcient data model will

denormalize data and use the
storage engine order.

To create a good data model

understand the queries your
application requires.

Multiple API’s?

initially only a Thrift / RPC
API, used by language speciﬁc
clients.

Multiple API’s...

Cassandra Query Language
(CQL) started as a higher
level, declarative alternative.

Multiple API’s...

CQL 3 brings many changes.
Currently in Beta in
Cassandra v1.1

CQL 3 uses

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

Twitter Clone
Previously done with Thrift at WDCNZ

“Hello @World #Cassandra - Apache
Cassandra in action”
http://vimeo.com/49762233

Twitter clone...

using CQL 3 via the cqlsh
tool.
bin/cqlsh -3

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

Keyspace is

a namespace container.

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

Table is

a sparse collection of well
known, ordered columns.

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

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

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

Data Model (so far)

User

Data Model (so far)
CF /
User
Value

user_name Primary Key

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

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

Data Model (so far)
CF /
User Tweet
Value

user_name Primary Key Field

tweet_id Primary Key

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

UserTweets Table...
cqlsh:cass_college> INSERT INTO UserTweets
... 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

UserTweets Table...
cqlsh:cass_college> select * from UserTweets where
user_name='fred' and tweet_id=1;

-----------+----------+-----------+--------------------------
fred | 1 | The Tweet | 2012-11-06 10:26:56+1300

UserTweets Table...
cqlsh:cass_college> INSERT INTO UserTweets
... VALUES
... (2, 'Second Tweet', 'fred', 1352150816918);

cqlsh:cass_college> select * from UserTweets where user_name = 'fred';
-----------+----------+--------------+--------------------------
fred | 1 | The Tweet | 2012-11-06 10:26:56+1300
fred | 2 | Second Tweet | 2012-11-06 10:26:56+1300

UserTweets Table...
cqlsh:cass_college> select * from UserTweets where user_name = 'fred' order by
tweet_id desc;

-----------+----------+--------------+--------------------------
fred | 2 | Second Tweet | 2012-11-06 10:26:56+1300
fred | 1 | The Tweet | 2012-11-06 10:26:56+1300

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

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

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

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

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

Relationships
CREATE TABLE Followers
(
user_name text,
follower text,
PRIMARY KEY (user_name, follower)
);

CREATE TABLE Following
(
user_name text,
following text,
PRIMARY KEY (user_name, following)
);

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

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

Aaron Morton
@aaronmorton
www.thelastpickle.com

Licensed under a Creative Commons Attribution-NonCommercial 3.0 New Zealand License

C*ollege Credit: Data Modeling for Apache Cassandra

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