Download - Using Apache Cassandra: What is this thing, and how do I use it?

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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


Cassandra - Intro

• Based on Amazon Dynamo and Google BigTable papers

• Shared nothing

• Distributed

• Data safe as possible

• Predictable scaling

4

Dynamo

BigTable


Cassandra - More than one server

• All nodes participate in a cluster

• Shared nothing

• Add or remove as needed

•More capacity? Add a server

5

• 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


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

6

Each node stores 3/4 of clusters total data.


Cassandra - Geographically Distributed

• Client writes local

• Data syncs across WAN

• Replication Factor per DC

7

Single coordinator


Cassandra - Consistency

• Consistency Level (CL)

• Client specifies per read or write

8

• ALL = All replicas ack

• QUORUM = > 51% of replicas ack

• LOCAL_QUORUM = > 51% in local DC ack

• ONE = Only one replica acks


Cassandra - Transparent to the application

• A single node failure shouldn’t bring failure

• Replication Factor + Consistency Level = Success

• This example:

• RF = 3

• CL = QUORUM

9

>51% Ack so we are good!


Application Example - Layout

• Active-Active

• Service based DNS routing

10

Cassandra Replication


Application Example - Uptime

11

• Normal server maintenance

• Application is unaware

Cassandra Replication


Application Example - Failure

12

• Data center failure

• Data is safe. Route traffic.

33

Another happy user!


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


Cassandra 2.0 - Big new features


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?


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


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




UPDATE USERS SET email = ’[email protected]’, ...WHERE username = ’jbellis’IF email = ’[email protected]’;

INSERT INTO USERS (username, email, ...)VALUES (‘jbellis’, ‘[email protected]’, ... )IF NOT EXISTS;

Using LWT

• Don’t overwrite an existing record

• Only update record if condition is met


mailto:[email protected]






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


http://www.slideshare.net/planetcassandra/c-summit-2013-eventual-consistency-hopeful-consistency-by-christos-kalantzis




Installing Cassandra


Download Cassandra


Extract Cassandra


Setup Data and Log Directories


Start Cassandra


Installing Cassandra Python Driver


Python Cassandra Driver


Install Python Cassandra Driver


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)


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) ) """)


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)


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)


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))


Run It


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


http://cassandra.apache.org

http://cassandra.apache.org

https://github.com/datastax

https://github.com/datastax

http://www.datastax.com/docs

http://www.datastax.com/docs

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

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

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

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

http://planetcassandra.org

http://planetcassandra.org

http://planetcassandra.org/Download/DataStaxCommunityEdition

http://planetcassandra.org/Download/DataStaxCommunityEdition

http://planetcassandra.org/Learn/CassandraCommunityWebinars

http://planetcassandra.org/Learn/CassandraCommunityWebinars

http://planetcassandra.org/Learn/CassandraSummit

http://planetcassandra.org/Learn/CassandraSummit

Download - Using Apache Cassandra: What is this thing, and how do I use it?

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