Data  modeling  with  Apache  Cassandra

Marko Švaljek @msvaljek

About  me •  Software Developer at Kapsch •  Zagreb Cassandra Meetup

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

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

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

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

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

Data  Organization

Wide  Row

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

Create  table CREATE TABLE employees (

name text PRIMARY KEY,age int,role text

);

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

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

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

How  it’s  stored

•  Every row is a partition •  There is no “next” row

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

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)

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

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

One  to  Many  Users

CREATE TABLE users ( username text, first_name text, last_name text, email text, PRIMARY KEY (username));

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));

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));

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));

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);

Q  &  A Thank you!

Don’t be afraid of writes!

Join Zagreb Cassandra Users!

@msvaljek

msvaljek@gmail.com