Ruby Driver Explained: DataStax Webinar May 5th 2015

Apache CassandraRuby Driver explained

IntroductionCassandra Overview

© 2015 DataStax, All Rights Reserved.

Datacenter Datacenter

Cassandra Topology

3

Node

NodeNode

Node

Client Client

Node

NodeNode

Node

Client Client

Cluster



Request Coordinator

4

Node

NodeNode

Node

Client Client

Node

NodeCoordinator

Node

Client Client

Coordinator node:Forwards requeststo corresponding replicas


Datacenter

Row Replica

5

Replica

NodeNode

Replica

Client Client

Datacenter

Node

Node

Replica

Client Client

Coordinator

Replica node:Stores a slice of total rows of each keyspace

Quick StartInstallation and Usage


Installation

7

gem 'cassandra-driver', '~> 1.0.0'

gem install cassandra-driver


Usage

8

require 'cassandra'

cluster = Cassandra.cluster

cluster.each_host do |h| puts "Host #{h.ip}: datacenter=#{h.datacenter} rack=#{h.rack}" end

keyspace = 'system' session = cluster.connect(keyspace)

future = session.execute_async('SELECT * FROM schema_columnfamilies')

future.on_success do |rows| rows.each do |row| puts “Table: #{row[‘keyspace_name']}.#{row['columnfamily_name']}" end end

future.join

Asynchronous ExecutionIO Reactor, Request Pipelining and Future Composition


Asynchronous Core

10

Application Thread

Business Logic

Driver

Background Thread

IO Reactor


Request Pipelining

11

Client

WithoutRequest Pipelining

Server

Client Server WithRequest Pipelining

1

2

2

3

1

3

1

2

3

1

2

3


Future Composition

12

select_user = session.prepare("SELECT * FROM users WHERE id = ?") select_page = session.prepare("SELECT * FROM pages WHERE slug = ?") user_ids = [1, 2, 3, 4] futures = user_ids.map do |id| future = session.execute_async(select_user, id)

future.then do |users| user = users.first future = session.execute_async(select_page, user[‘username'])

future.then do |pages| page = pages.first

User.new(user, Page.new(page)) end end end Cassandra::Future.all(futures).get


Future Composition

13






Future Composition

14






Future Composition

15






Future Composition

16






Future Composition

17






Future Composition

18

[#<User @id=1 @username="avalanche123"; @page=#<Page @slug="avalanche123" ... > ... >, ... ]

Load BalancingPrinciples and Implementations


Application Driver

Load Balancing

20

ApplicationThread

Node

Pool

SessionPool

Pool

Pool

ApplicationThread

ApplicationThread

Client Cluster

Node

Node

Node

Load Balancing Policy


Application Driver

Load Balancing

20

ApplicationThread

Node

Pool

SessionPool

Pool

Pool

ApplicationThread

ApplicationThread

Client Cluster

Node

Node

Node



Application Driver

Load Balancing

20

ApplicationThread

Node

Pool

SessionPool

Pool

Pool

ApplicationThread

ApplicationThread

Client Cluster

Node

Node

Node



Datacenter

Datacenter

DataCenter Aware Balancing

21

Node

Node

NodeClient

Node

Node

Node

Client

Client

Client

Client

Client

Local nodes are queried first, if non are available, the request could be sent to a remote node.


Token Aware Balancing

22

Route request directly to Replicas

Node

Node

ReplicaNode

Client

Replica

Replica

Uses prepared statement metadata to get the token

Fault ToleranceSources of Failure and Error Handling


Fault Tolerance

24

Coordinator

Node Replica

Replica

ReplicaNode

Business Logic

Driver

Application

© 2015 DataStax, All Rights Reserved. 25

Coordinator

Node Replica

Replica

ReplicaNode

Business Logic

Driver

Application

Invalid Requests

Network Timeouts

Server ErrorsPossible Failures


Application Driver

Automatic Retry of Server Errors

26

ApplicationThread

Node

Pool

SessionPool

Pool

Pool

ApplicationThread

ApplicationThread

Client Cluster

Node

Node

Node



Application Driver


26

ApplicationThread

Node

Pool

SessionPool

Pool

Pool

ApplicationThread

ApplicationThread

Client Cluster

Node

Node

Node



Application Driver


26

ApplicationThread

Node

Pool

SessionPool

Pool

Pool

ApplicationThread

ApplicationThread

Client Cluster

Node

Node

Node



Coordinator

Node Replica

Replica

ReplicaNode

Business Logic

Driver

Application

Unreachable Consistency


Coordinator

Node Replica

ReplicaNode

28

Replica

Business Logic

Driver

Application

Read / Write Timeout Error


Coordinator

Node Replica

ReplicaNode

28

Replica

Business Logic

Driver

Application



Coordinator

Node Replica

ReplicaNode

28

Replica

Business Logic

Driver

Application


read / write timeout


Coordinator

Node Replica

Replica

ReplicaNode

Business Logic

Driver

Application

Unavailable Error


Coordinator

Node Replica

Replica

ReplicaNode

Business Logic

Driver

Application

Unavailable Error

unavailable


Error Handling

Address ResolutionTopology Aware Client



Multiple Addresses

32

Node

NodeNode

Node

Client Client

Node

NodeNode

Node

Client Client

Within Datacenter: Private IPs

Across Datacenters: Public IPs


Application Driver

Address Resolution

33

ApplicationThread

ApplicationThread

ApplicationThread

Client Cluster


Application Driver

Address Resolution

33

ApplicationThread Node

Cluster

ApplicationThread

ApplicationThread

Client Cluster

Address Resolution Policy


Application Driver

Address Resolution

33


Cluster

ApplicationThread

ApplicationThread

Client Cluster

Node

Node

Node


Control Connection


Application Driver

Address Resolution

33


Cluster

ApplicationThread

ApplicationThread

Client Cluster

Node

Node

Node


Control Connection


Application Driver

Address Resolution

33


Pool

Cluster

Pool

Pool

Pool

ApplicationThread

ApplicationThread

Client Cluster

Node

Node

Node


Control Connection

Session


EC2 Multi-Region Address Resolution

34

Questions and Links• Documentation • Code • Example Web-app

http://datastax.github.io/ruby-driver/

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

https://github.com/avalanche123/cassandra-web

Ruby Driver Explained: DataStax Webinar May 5th 2015

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