Intro to Cassandra and CassandraObject

Cassandra &
CassandraObject
Michael Koziarski
michael@koziarski.com

The Ring
A

F B

E C

D

The Ring
someKey

A

F B

E C

D

RandomPartitioner OrderPreservingPartitioner
MD5(key) key

Replication Factor
someKey

A

F B

E C

D

RF = 2

Replication Factor
someKey

A

F B

E C

D

RF = 3

Consistency Level
GET
'someKey'

A

F B

E C

D

ConsistencyLevel.ONE

Consistency Level
GET
'someKey'

A

F B

E C

D

ConsistencyLevel.QUORUM

Consistency Level
GET
'someKey'

A

F B

E C

D

ConsistencyLevel.ALL

Fault Tolerance
GET
'someKey'

A

F DEAD

E C

D

ConsistencyLevel.QUORUM

Fault Tolerance
GET
'someKey'

A

F

E C

D

Elastic
NEW
A

F B

E C

D

Key Value Store

Some
someKey
Value

Row (Column Family)

ﬁrstName Michael
someKey
lastName Koziarski

Row (Super Column Family)
ﬁrstName Michael
someSubColumn
lastName Koziarski
someKey

ﬁrstName Kate
otherSubColumn
lastName Koziarski

Column
{
'name': 'first_name',
'value': 'Michael',
'timestamp': 1276040575
}

Column

{
'first_name': "Michael"
}

Column Family

Users["koz"] = {
'first_name': 'Michael',
'last_name': 'Koziarski'
}

Super Column Family
UserAddresses["koz"] = {
"home" : {
"suburb": "Berhampore"
"city": "Wellington",
"country": "New Zealand"
},
"office" : {
"suburb": "CBD"
"city": "Wellington",
"country": "New Zealand"
}
}

Don’t let the name fool
you

One to Many

Timeline["nzkoz"] = {
uuid_one: "http://twitter.com/chadfowler/status/15740739666",
uuid_two: "http://twitter.com/dhh/status/15740689762",
uuid_three: "http://twitter.com/glv/status/15740546908"
}

<ColumnFamily CompareWith="TimeUUIDType" Name="Timeline"/>

Model

User
ﬁrstName
lastName
dateOfBirth

Query

SELECT firstName, lastName
FROM `users`
WHERE dateOfBirth < '1992-‐06-‐09'

Query
SELECT dateOfBirth
FROM `users`
WHERE firstName = 'Michael'
AND
lastName = 'Koziarski'

Query

SELECT firstName, lastName
FROM `users`
WHERE YEAR(dateOfBirth) = 1980

Query

SELECT COUNT(DISTINCT firstName)
FROM `users`
WHERE dateOfBirth < '1992-‐06-‐09'

Populate a data model
which enables them

Users

Users["koz"] = {
'first_name': "Michael",
'last_name': "Koziarski"
}

Users

Users["koz"] = {
'first_name': "Michael",
'last_name': "Koziarski"
}

connection.get(:Users, "koz")

Koziarski Family
UsersByLastName["koziarski"] = {
uuid_one: "koz"
uuid_two: "kate"
}

Koziarski Family
UsersByLastName["koziarski"] = {
uuid_one: "koz"
uuid_two: "kate"
}

connection.get(:UsersByLastName, "koziarski").values.map do |key|
connection.get(:Users, key)
end

Share my Birthday
UsersByDOB["1980-‐08-‐15"] = {
uuid_one: "koz"
}

Share my Birthday
UsersByDOB["1980-‐08-‐15"] = {
uuid_one: "koz"
}

connection.get(:UsersByDOB, "1980-‐08-‐15")

Users Born in 1980
UsersByDOB["1980-‐08-‐15"] = {
uuid_one: "koz"
}

Users Born in 1980
UsersByDOB["1980-‐08-‐15"] = {
uuid_one: "koz"
}

connection.get_range(:UsersByDOB, :start=>"1980", :finish=>"1981")

Users Born in 1980
UsersByDOB["1980-‐08-‐15"] = {
uuid_one: "koz"
}


Only with OrderPreservingPartitioner

A Column Family per
Query

Do you really need
Cassandra?

class Customer < CassandraObject::Base
attribute :first_name, :type => :string
attribute :last_name, :type => :string
attribute :date_of_birth, :type => :date
attribute :signed_up_at, :type => :time_with_zone

validate :should_be_cool

key :uuid

index :date_of_birth

association :invoices, :unique=>false, :inverse_of=>:customer

private

def should_be_cool
unless ["Michael", "Anika", "Evan", "James"].include?(first_name)
errors.add(:first_name, "must be that of a cool person")
end
end
end

Not Compatible

def index
@people = @customer.people.order(params[:order]).
limit(params[:limit]).
where(...)
end

Compatible
def create
@person = Customer.new params[:customer]
if @person.save
redirect_to @person
else
render :action=>'new'
end
end

Compatible

<%= form_for(@customer) do |customer| %>
<%= customer.error_messages %>
<%= customer.text_field :first_name %>
<%= customer.submit "Save" %>
<% end %>

class Invoice < CassandraObject::Base
attribute :number, :type=>:integer
attribute :total, :type=>:float
attribute :gst_number, :type=>:string

# indexes can have a single entry also.
index :number, :unique=>true

# bi-‐directional associations with read-‐repair support.
association :customer, :unique=>true, :inverse_of=>:invoices

# Read migration support
migrate 1 do |attrs|
attrs["total"] ||= rand(2000) / 100.0
end

attrs["gst_number"] = "66-‐666-‐666"
end

key :natural, :attributes => :number
end

Attributes
attribute :last_name, :type => :string
attribute :date_of_birth, :type => :date
attribute :signed_up_at, :type => :time_with_zone
attribute :number, :type => :integer
attribute :total, :type => :float
attribute :gst_number, :type => :string

Attributes

@customer.first_name = "Michael"
@customer.attributes= {:first_name=>"Michael"}

Validations

def should_be_cool
end
end

Validations

def should_be_cool
end
end

@customer.first_name = "Marcel"
@customer.valid? # => false

Validations

validates_confirmation_of :tos
validates_format_of :gst_number, :with=> /.../
validates_length_of :first_name, :max=>123

Key Selection Matters
UsersByDOB["1980-‐08-‐15"] = {
uuid_one: "koz"
}


Keys

key :uuid

"bf1ba5da-‐735a-‐11df-‐8b47-‐377649cf993b"

Keys

key :natural, :attributes => :number

Custom Key Factories

key RedisKeyFactory.new(REDIS_CONNECTION, "customer_key")

Custom Key Factories
class RedisKeyFactory
def initialize(connection, key)
@connection, @key = connection, key
end

def next_key(object)
@connection.incr(@key)
end

# Parse should create a new key object from the 'to_param' format
def parse(string)
string.to_i
end

# create should create a new key object from the cassandra format.
def create(string)
string.to_i
end
end

Migrations
class AddLicenseNameToArticle < ActiveRecord::Migration
def self.up
add_column :articles, :license_name, :string, :default=>"Exclusive"

execute "UPDATE articles SET license_name = 'Exclusive'
WHERE price_first IS NOT NULL"
execute "UPDATE articles SET license_name = 'Syndicated'
WHERE price_first IS NULL"
end

def self.down
remove_column :articles, :license_name
end
end

Migrations

{
'price_first': 45,
'schema_version': 0
}

Migrations
class Article < CassandraObject::Base
attribute :price_first, :type=>:float
attribute :license_name, :type=>:string

if attrs[:price_first]
attrs[:license_name] = "Exclusive"
else
attrs[:license_name] = "Syndicated"
end
end
end

Migrations
attribute :price_first, :type=>:float
attribute :license_name, :type=>:string

if attrs[:price_first]
attrs[:license_name] = "Exclusive"
else
attrs[:license_name] = "Syndicated"
end
end
end

@article = Article.get("some-‐old-‐story")
@article.license_name # => "Exclusive"

Migrations

{
'price_first': 45,
'schema_version': 1,
'license_name': 'Exclusive'
}

Indexes
attribute :slug, :type=>:string
key :uuid
index :slug, :unique=>true
end

connection.insert(:ArticlesBySlug, @article.slug,
{UUID.new => @article.key})

Indexes
attribute :slug, :type=>:string
key :uuid
index :slug, :unique=>true
end

connection.insert(:ArticlesBySlug, @article.slug,

@article = Article.find_by_slug("some-‐slug")

Indexes
attribute :publication_date, :type=>:date
key :uuid
index :publication_date, :unique=>false
end

connection.insert(:ArticlesByPublicationDate,
@article.publication_date,

Indexes
attribute :publication_date, :type=>:date
key :uuid
index :publication_date, :unique=>false
end

connection.insert(:ArticlesByPublicationDate,
@article.publication_date,

@article = Article.find_all_by_publication_date(Date.today -‐ 1)

Read-Repair
results = []
connection.get(:ArticlesByPublicationDate, date).each do |(uuid, key)|
article = Article.get(uuid)
if article.publication_date != date
connection.delete(:ArticlesByPublicationDate, date, uuid)
else
results << article
end
end
results

Associations
class Invoice < CassandraObject::Base
association :customer, :unique=>true, :inverse_of=>:invoices
end

class Customer < CassandraObject::Base
association :invoices, :unique=>false, :inverse_of=>:customer
end

@customer.invoices.create! params[:invoice]

@invoice.customer

Thanks!
Michael Koziarski
michael@koziarski.com

http://github.com/NZKoz/cassandra_object
http://cassandra.apache.org/

Intro to Cassandra and CassandraObject

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