Cassandra is a NoSQL Column Family oriented database with a built in scalability. More and more companies are faced with the scale challenge every day and Cassandra is often picked as a weapon of choice. Cassandra being NoSQL does not mean that data modeling does not matter, in reality it is crucial to any successful use out there. Lately more and more developers are asking me to tell more about the data modeling (compared with the relational perspective). That’s what this talks is all about.

1. Data modeling with
Apache Cassandra
Marko Švaljek
@msvaljek

2. About me
• Software Developer at Kapsch
• Zagreb Cassandra Meetup

3. About Cassandra
• Written in Java
• Wide Row Store
• Masterless
• DataStax

4. About Cassandra
• No Single Point of failure ✓
• Cross Datacenter ✓
• Linear Scaling ✓
• Data modeling ?

5. Data Model
• Highly denormalized
• No foreign keys
• No referential integrity
• No joins

6. Compared to Relational
• Think about the questions up front
• No penalty for wide rows
• Disk is cheap
• Bring on the writes

7. Cassandra Objects
• Keyspace (database)
• Table
• Primary key
• Index

8. Data Organization

9. Wide Row

10. CQL
• Cassandra Query Language
• Similar to SQL
• Learning curve
• No code reading

11. Create table
CREATE TABLE employees (
name text PRIMARY KEY,
age int,
role text
);

12. Inserting
INSERT INTO employees
(name, age)
VALUES ('mario', 38);
INSERT INTO employees
(name, age)
VALUES ('tom', 24);

13. Selecting
SELECT * FROM employees;
name | age | role
-------+-----+------
tom | 24 | DEV
mario | 38 | SM

14. Hmm …
SELECT *
FROM employees
WHERE age > 20;
Bad Request: No indexed
columns present in by-columns
clause with Equal operator

15. How it’s stored
• Every row is a partition
• There is no “next” row

16. Primary key
CREATE TABLE employees2 (
company text,
name text,
age int,
role text,
PRIMARY KEY (company, name)
);

17. Primary key
company | name | age | role
---------+-------+-----+------
B | john | 25 | DEV
B | peter | 22 | DEV
A | kate | 33 | PM
A | mario | 38 | SM
A | neno | 32 | DEV
PRIMARY KEY (company, name)

18. Primary key
company | name | age | role
---------+-------+-----+------
B | john | 25 | DEV
B | peter | 22 | DEV
A | kate | 33 | PM
A | mario | 38 | SM
A | neno | 32 | DEV

19. Primary key
SELECT *
FROM employees2
WHERE company = 'A'
AND name > 'kate';
company | name | age | role
---------+-------+-----+------
A | mario | 38 | SM
A | neno | 32 | DEV

20. Primary key
PRIMARY KEY (a, b)
PRIMARY KEY ((x, y), z, w)
Partition Key (row) – just the 1st
Clustering Columns – the rest

21. One to Many
Users
CREATE TABLE users (
username text,
first_name text,
last_name text,
email text,
PRIMARY KEY (username)
);

22. One to Many
Videos
CREATE TABLE videos (
video_id uuid,
video_name text,
username text,
description text,
tags text,
upload_date timestamp,
PRIMARY KEY (video_id)
);

23. One to Many
User videos
CREATE TABLE username_video_ind (
username text,
video_id uuid,
upload_date timestamp,
video_name text,
PRIMARY KEY (username, video_id)
);

24. Many to Many
Comments
CREATE TABLE comments_by_video (
video_id uuid,
username text,
comment_time timestamp,
comment text,
PRIMARY KEY (video_id, username)
);
CREATE TABLE comments_by_user (
username text,
videoid uuid,
comment_time timestamp,
comment text,
PRIMARY KEY (username, videoid)
);

25. Reverse ordering
CREATE TABLE credit_transaction (
username text,
type text,
date_time timestamp,
credits int,
PRIMARY KEY (username, datetime, type)
) WITH CLUSTERING ORDER BY
(datetime DESC, type ASC);

26. Q & A
Thank you!
Don’t be afraid of writes!
Join Zagreb Cassandra Users!
@msvaljek
msvaljek@gmail.com