Introduction to Cassandra Basics

Introduction to CassandraNick Bailey@nickmbailey

Monday, October 28, 13

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Who am I?

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What’s DataStax?

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On to the good stuff!

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Why Cassandra?

Cluster Architecture

Node Architecture

Data Modeling

Wrap up

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Why Cassandra?

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Time for buzz words!

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Big Data!

NoSQL!


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Big Data

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• Gartner: “...high-volume, high-velocity and high-variety...”

• 2 sides of ‘big data’• Analytics• Real-time


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NoSQL

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• A terrible label

• Covers a wide range of DBs• Cassandra• Redis• MongoDB• HBase• ...


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Started by Facebook

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Dynamo (Amazon)+

Big Table (Google)

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Cassandra is great for...

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• Massive, linear scaling (e.g. CERN hadron collider, Barracuda Networks)

• Extremely heavy writes(e.g. BlueMountain Capital – financial tick data)

• High availability(e.g. eBay, Eventbrite, Netflix, SoundCloud, HeathCare Anytime, Comcast, GoDaddy, Sony Entertainment Network)


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http://techblog.netflix.com/2012/07/lessons-netflix-learned-from-aws-storm.html




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One size does not fit all

Polyglot persistence

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More Resources

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• PlanetCassandra.org

• Blog

• 5 minute interviews


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Cluster Architecture

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75

0

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Data Distribution

Hash_Function(Partition Key) >> Token


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Replication


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Failure Modes


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Consistency Level

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• Multiple options• ONE• QUORUM• ALL• LOCAL_QUORUM• ...

• Can be specified per request


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Quorum


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Consistency

WriteCL: ONE


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Consistency

ReadCL: One


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Failure Types

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• UnavailableException• Didn’t even try

• TimedOutException• Possible success or failure


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Multi DC


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Gossip

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• Manages cluster state• Nodes up/down• Nodes joining/leaving

• Decentralized


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Snitch

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• Responsible for determining cluster topology

• Tracks node responsiveness

• Simple, PropertyFile, Ec2Snitch, etc...


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Node Architecture

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Write Path

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commit log

Memtable

SSTable

Write

Memory

Disk


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Read Path

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Memtable

SSTable

Read

SSTable

Memory

Disk


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Data Modeling

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CQLCassandra Query Language

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Terminology

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• Keyspace

• Table (Column Family)

• Row

• Column

• Partition Key

• Clustering Key (Optional)


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CREATE KEYSPACE packagetracker WITH REPLICATION = { 'class' : 'SimpleStrategy', 'replication_factor' : 1 };

CREATE KEYSPACE packagetracker WITH REPLICATION = { 'class' : 'NetworkTopologyStrategy', 'dc1' : 2, 'dc2' : 2};

CREATE TABLE events (package_id text,status_timestamp timestamp,location text,notes text,PRIMARY KEY (package_id, status_timestamp)

);

For Example:

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Constructs

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Basic Data Types

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• blob

• int

• text

• long

• uuid

• etc


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More Data Modeling Constructs

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• Collections• map, set, list

• Time to live (TTL)

• Counters

• Secondary Indexes


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Approaching Data Modeling

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• Model your queries, not your data• Optimize your data model for reads

• Don’t be afraid to denormalize

• You will get it wrong, iterate


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An Example:User Logins

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What are the last 10 locations nickmbailey logged in from?

SELECT time, location FROM logins WHERE user = ‘nickmbailey’ ORDER BY time DESC LIMIT 10;

The Query

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CREATE COLUMN FAMILY logins ( user text, time timestamp, location text, PRIMARY KEY (user, time));

The Query

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Additional ColumnsClustering Key Partition Key


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CREATE COLUMN FAMILY logins ( user text, time timestamp, location text, PRIMARY KEY (user, time));

The Query

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User Time Locationnickmbailey 2013-07-19 09:22:18 Austin, Texas

nickmbailey 2013-07-19 14:49:27 Blacksburg, Virginia

jsmith 2013-07-20 07:59:34 Atlanta, Georgia

Partition key Primary key


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Time-series data

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• By far, the most common data model

• Event logs

• Metrics

• Sensor Data

• Etc


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When was the last time nickmbailey logged in from San Francisco, California?

SELECT time FROM logins WHERE user = ‘nickmbailey’ and location=‘San Francisco, California’;

Another Query

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User Time Location

nickmbailey 2013-07-19 09:22:18 Austin, Texas

nickmbailey 2013-07-19 14:49:27 Blacksburg, Virginia



nickmbailey 2013-04-19 14:49:27 San Francisco, California

... ... ...

jsmith 2013-07-20 07:59:34 Atlanta, Georgia


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When was the last time nickmbailey logged in from Austin, Texas?

SELECT time FROM logins_by_location WHERE user = ‘nickmbailey’ and location=‘San Francisco, California’;

CREATE COLUMN FAMILY logins_by_location (user text, time timestamp, location text, PRIMARY KEY (user, location));

Another Query

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When was the last time nickmbailey logged in from Austin, Texas?

SELECT time FROM logins_by_location WHERE user = ‘nickmbailey’ and location=‘San Francisco, California’;

CREATE COLUMN FAMILY logins_by_location (user text, time timestamp, location text, PRIMARY KEY (user, location));

Another Query

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User Location Time

nickmbailey Austin, Texas 2013-07-19 09:22:18

nickmbailey Blacksburg, Virginia 2013-07-19 14:49:27

nickmbailey San Francisco, California 2013-07-19 14:49:27


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Denormalize

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• Create materialized views of the same data to support different queries

• Storage space is cheap, Cassandra is fast


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Debugging your data model

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cqlsh> tracing on;Now tracing requests.

cqlsh:foo> INSERT INTO test (a, b) VALUES (1, 'example');Tracing session: 4ad36250-1eb4-11e2-0000-fe8ebeead9f9

activity | timestamp | source | source_elapsed-------------------------------------+--------------+-----------+---------------- execute_cql3_query | 00:02:37,015 | 127.0.0.1 | 0 Parsing statement | 00:02:37,015 | 127.0.0.1 | 81 Preparing statement | 00:02:37,015 | 127.0.0.1 | 273 Determining replicas for mutation | 00:02:37,015 | 127.0.0.1 | 540 Sending message to /127.0.0.2 | 00:02:37,015 | 127.0.0.1 | 779

Messsage received from /127.0.0.1 | 00:02:37,016 | 127.0.0.2 | 63 Applying mutation | 00:02:37,016 | 127.0.0.2 | 220 Acquiring switchLock | 00:02:37,016 | 127.0.0.2 | 250 Appending to commitlog | 00:02:37,016 | 127.0.0.2 | 277 Adding to memtable | 00:02:37,016 | 127.0.0.2 | 378 Enqueuing response to /127.0.0.1 | 00:02:37,016 | 127.0.0.2 | 710 Sending message to /127.0.0.1 | 00:02:37,016 | 127.0.0.2 | 888


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A note on Transactions

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• In general, you want to construct your data model around them

• The latest version of Cassandra has ‘Compare and swap’• An implementation of Paxos• ...IF NOT EXISTS;• ...IF column1 = ‘value’;


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CCM

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• CCM - Cassandra Cluster Manager• https://github.com/pcmanus/ccm

• Warning: not lightweight

• Example:• ccm create test -v 2.0.1• ccm populate -n 3• ccm start


https://github.com/pcmanus/ccm

https://github.com/pcmanus/ccm

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Clients

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• Cqlsh• Bundled with Cassandra

• Drivers• java: https://github.com/datastax/java-driver• python: https://github.com/datastax/python-driver• .net: https://github.com/datastax/csharp-driver• and more: http://www.datastax.com/download/

clientdrivers


https://github.com/datastax/java-driver

https://github.com/datastax/java-driver

https://github.com/datastax/python-driver

https://github.com/datastax/python-driver

https://github.com/datastax/csharp-driver

https://github.com/datastax/csharp-driver

http://www.datastax.com/download/clientdrivers




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Get Help

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• IRC: #cassandra on freenode

• Mailing Lists

• Stack Overflow

• DataStax Docs• http://www.datastax.com/docs


http://www.datastax.com/docs

http://www.datastax.com/docs

Introduction to Cassandra Basics

Technology

Transcript of Introduction to Cassandra Basics