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@PatrickMcFadin

Patrick McFadin Chief Evangelist/Solution Architect - DataStax

Cassandra : Introduction

Who I am

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• Patrick McFadin • Solution Architect at DataStax • Cassandra MVP • User for years • Follow me for more:

I talk about Cassandra and building scalable, resilient apps ALL THE TIME!

@PatrickMcFadin

Dude. Uptime == $$

Five Years of Cassandra

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0.1 0.3 0.6 0.7 1.0 1.2...

2.0

DSE

Jul-08

Cassandra - An introduction

Cassandra - Intro

• Based on Amazon Dynamo and Google BigTable paper • Shared nothing • Data safe as possible • Predictable scaling

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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

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Cassandra - Locally Distributed

• Client writes to any node • Node coordinates with others • Data replicated in parallel • Replication factor: How many

copies of your data? • RF = 3 here

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Cassandra - Geographically Distributed

• Client writes local • Data syncs across WAN • Replication Factor per DC

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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

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!

Cassandra Applications - Drivers

• DataStax Drivers for Cassandra • Java • C# • Python •more on the way

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Cassandra Applications - Connecting

• Create a pool of local servers • Client just uses session to interact with Cassandra

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!contactPoints = {“10.0.0.1”,”10.0.0.2”}!!keyspace = “videodb”!!public VideoDbBasicImpl(List<String> contactPoints, String keyspace) {!

! cluster = Cluster! .builder()! .addContactPoints(!! contactPoints.toArray(new String[contactPoints.size()]))! .withLoadBalancingPolicy(Policies.defaultLoadBalancingPolicy())! .withRetryPolicy(Policies.defaultRetryPolicy())! .build();!! session = cluster.connect(keyspace);! }

Cassandra Applications - Load balancing• Token aware - Request sent to primary node with data • Calls can be asynchronous and in parallel

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Cassandra Applications - Fault tolerance

• Try first with a Consistency Level of QUORUM • If fails, retry with Consistency Level ONE

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Client Node

Node Replica

Replica

NodeReplica

Application Example - Layout

• Active-Active • Service based DNS routing

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Cassandra Replication

Application Example - Uptime

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• Normal server maintenance • Application is unaware

Cassandra Replication

Application Example - Failure

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• Data center failure • Data is safe. Route traffic.

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Another happy user!

Cassandra Users and Use Cases

Netflix!• If you haven’t heard their story… where have you been? • 18B market cap — Runs on Cassandra • User accounts • Play lists • Payments • Statistics

Spotify

•Millions of songs. Millions of users. • Playlists • 1 billion playlists • 30+ Cassandra clusters • 50+ TB of data • 40k req/sec peak

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http://www.slideshare.net/noaresare/cassandra-nyc

Instagram(Facebook)

• Loads and loads of photos. (Probably yours) • All in AWS • Security audits • News feed • 20k writes/sec. 15k reads/sec.

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