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Jeremiah JordanLead Software Engineer/Support

Using Apache Cassandra for Big DataWhat is this thing, and how do I use it?

1Monday, October 14, 13

Who I am• Jeremiah Jordan

• Lead Software Engineer in Support at DataStax

• Previously Senior Architect at Morningstar, Inc.

• Using Cassandra since 0.6

• Before that, wrote code for the F22

Monday, October 14, 13

Cassandra - An introduction

Monday, October 14, 13

Cassandra - Intro

• Based on Amazon Dynamo and Google BigTable papers

• Shared nothing

• Distributed

• Data safe as possible

• Predictable scaling

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Dynamo

BigTable

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Cassandra - More than one server

• All nodes participate in a cluster

• Shared nothing

• Add or remove as needed

•More capacity? Add a server

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• Each node owns a number of tokens• Tokens denote a range of keys

• 4 nodes? -> Key range/4• Each node owns 1/4 the data

Monday, October 14, 13

Cassandra - Locally Distributed

• Client writes to any node

• Node coordinates with others

• Data replicated in parallel

• Replication factor (RF): How many copies of your data?

• RF = 3 here

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Each node stores 3/4 of clusters total data.

Monday, October 14, 13

Cassandra - Geographically Distributed

• Client writes local

• Data syncs across WAN

• Replication Factor per DC

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Single coordinator

Monday, October 14, 13

Cassandra - Consistency

• Consistency Level (CL)

• Client specifies per read or write

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• ALL = All replicas ack

• QUORUM = > 51% of replicas ack

• LOCAL_QUORUM = > 51% in local DC ack

• ONE = Only one replica acks

Monday, October 14, 13

Cassandra - Transparent to the application

• A single node failure shouldn’t bring failure

• Replication Factor + Consistency Level = Success

• This example:

• RF = 3

• CL = QUORUM

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>51% Ack so we are good!

Monday, October 14, 13

Application Example - Layout

• Active-Active

• Service based DNS routing

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Cassandra Replication

Monday, October 14, 13

Application Example - Uptime

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• Normal server maintenance

• Application is unaware

Cassandra Replication

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Application Example - Failure

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• Data center failure

• Data is safe. Route traffic.

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Another happy user!

Monday, October 14, 13

Five Years of Cassandra

Jul-09 May-10 Feb-11 Dec-11 Oct-12 Jul-13

0.1 0.3 0.6 0.7 1.0 1.2...

2.0

DSE

Jul-08

Monday, October 14, 13

Cassandra 2.0 - Big new features

Monday, October 14, 13

SELECT * FROM usersWHERE username = ’jbellis’

[empty resultset]

Session 1SELECT * FROM usersWHERE username = ’jbellis’

[empty resultset]

Session 2

Lightweight transactions: the problem

INSERT INTO users (username,password)VALUES (’jbellis’,‘xdg44hh’)

INSERT INTO users (userName,password)VALUES (’jbellis’,‘8dhh43k’)

It’s a Race!

Who wins?

Monday, October 14, 13

LWT: details• 4 round trips vs 1 for normal updates

• Paxos - Paxos made easy

• Immediate consistency with no leader election or failover

• For reads, ConsistencyLevel.SERIAL

• http://www.datastax.com/dev/blog/lightweight-transactions-in-cassandra-2-0

Monday, October 14, 13

UPDATE USERS SET email = ’jonathan@datastax.com’, ...WHERE username = ’jbellis’IF email = ’jbellis@datastax.com’;

INSERT INTO USERS (username, email, ...)VALUES (‘jbellis’, ‘jbellis@datastax.com’, ... )IF NOT EXISTS;

Using LWT

• Don’t overwrite an existing record

• Only update record if condition is met

Monday, October 14, 13

LWT: Use with caution• Great for 1% of your application

• Eventual consistency is your friend• http://www.slideshare.net/planetcassandra/c-summit-2013-eventual-consistency-

hopeful-consistency-by-christos-kalantzis

Monday, October 14, 13

Installing Cassandra

Monday, October 14, 13

Download Cassandra

Monday, October 14, 13

Download Cassandra

Monday, October 14, 13

Download Cassandra

Monday, October 14, 13

Extract Cassandra

Monday, October 14, 13

Setup Data and Log Directories

Monday, October 14, 13

Start Cassandra

Monday, October 14, 13

Start Cassandra

Monday, October 14, 13

Installing Cassandra Python Driver

Monday, October 14, 13

Python Cassandra Driver

Monday, October 14, 13

Install Python Cassandra Driver

Monday, October 14, 13

Connect and Create a Keyspacefrom cassandra.cluster import Cluster

cluster = Cluster(['127.0.0.1'])session = cluster.connect()

log.info("creating keyspace...")KEYSPACE = "testkeyspace"session.execute(""" CREATE KEYSPACE IF NOT EXISTS %s WITH replication = { 'class': 'SimpleStrategy', 'replication_factor': '1' } """ % KEYSPACE)

Monday, October 14, 13

Create a Tablelog.info("setting keyspace...")session.set_keyspace(KEYSPACE)

log.info("creating table...")session.execute(""" CREATE TABLE IF NOT EXISTS mytable ( thekey text, col1 text, col2 text, PRIMARY KEY (thekey, col1) ) """)

Monday, October 14, 13

Insert a Rowquery = SimpleStatement(""" INSERT INTO mytable (thekey, col1, col2) VALUES ('key1', 'a', 'b') """, consistency_level=ConsistencyLevel.ONE)

log.info("inserting row")session.execute(query)

Monday, October 14, 13

Insert Rows (Prepared Statement)prepared = session.prepare(""" INSERT INTO mytable (thekey, col1, col2) VALUES (?, ?, ?) """)

for i in range(10): log.info("inserting row %d" % i) bound = prepared.bind(("key%d" % i, "b%d" % i, "c%d" % i)) session.execute(bound)

Monday, October 14, 13

Query Resultsfuture = session.execute_async(""" SELECT * FROM mytable WHERE thekey='key1' """)rows = future.result()

log.info("key\tcol1\tcol2")log.info("---\t----\t----")for row in rows: log.info("\t".join(row))

Monday, October 14, 13

Run It

Monday, October 14, 13

Cassandra Applications - Drivers

• DataStax Drivers for Cassandra

• Java

• C#

• Python

•more on the way

36Monday, October 14, 13

Find Out MoreCassandra: http://cassandra.apache.org

DataStax Drivers: https://github.com/datastax

Documentation: http://www.datastax.com/docs

Getting Started: http://www.datastax.com/documentation/gettingstarted/index.html

Developer Blog: http://www.datastax.com/dev/blog

Cassandra Community Site: http://planetcassandra.org

Download: http://planetcassandra.org/Download/DataStaxCommunityEdition

Webinars: http://planetcassandra.org/Learn/CassandraCommunityWebinars

Cassandra Summit Talks: http://planetcassandra.org/Learn/CassandraSummit

Monday, October 14, 13

©2013 DataStax Confidential. Do not distribute without consent. 38Monday, October 14, 13