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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.
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DATASTAX C*OLLEGE CREDIT:
DATA MODELLING FOR APACHE CASSANDRA
Aaron MortonApache Cassandra Committer, Data Stax MVP for Apache Cassandra
@aaronmortonwww.thelastpickle.com
Licensed under a Creative Commons Attribution-NonCommercial 3.0 New Zealand License
General GuidelinesAPI ChoiceExample
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.
General GuidelinesAPI Choice
Example
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.)
General GuidelinesAPI ChoiceExample
Twitter ClonePreviously 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 / Value User
user_name Primary Key
Tweet TableCREATE 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 / Value User Tweet
user_name Primary Key Field
tweet_id Primary Key
UserTweets TableCREATE TABLE UserTweets ( tweet_id bigint, user_name text, body text, timestamp timestamp, PRIMARY KEY (user_name, tweet_id));
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
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
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
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
UserTimelineCREATE TABLE UserTimeline ( tweet_id bigint, user_name text, body text, timestamp timestamp, PRIMARY KEY (user_name, tweet_id));
Data Model (so far)
CF / Value User Tweet User
TweetsUser
Timeline
user_name Primary Key Field Primary Key Primary Key
tweet_id Primary Key Primary KeyComponent
Primary KeyComponent
UserMetrics TableCREATE 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 / Value User Tweet User
TweetsUser
Timeline User Metrics
user_name Primary Key Field Primary
KeyPrimary
KeyPrimary
Key
tweet_id Primary Key
Primary KeyComponent
Primary KeyComponent
RelationshipsCREATE 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));
RelationshipsINSERT INTO Following (user_name, following, timestamp)VALUES ('bob', 'fred', 1352247749161);INSERT INTO Followers (user_name, follower, timestamp)VALUES ('fred', 'bob', 1352247749161);
Relationshipscqlsh: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
Data Model
CF / Value User Tweet User
TweetsUser
TimelineUser
MetricsFollows
Followers
user_name Primary Key Field Primary
KeyPrimary
KeyPrimary
KeyPrimary
KeyField
tweet_id Primary Key
Primary KeyComponent
Primary KeyComponent
Thanks.
Aaron Morton@aaronmorton
www.thelastpickle.com
Licensed under a Creative Commons Attribution-NonCommercial 3.0 New Zealand License
