hrx meetup group 8/20/2014: cassandra and how to scale your database

CassandraPretty Cool

HistoryGoogle Big Table

Amazon Dynamo

Today

Why Should You Care● Horizontal Scaling (basically auto sharding)

● Multiple Nodes - Highly Available

● Really Fast Writes

● Not too shabby at reads either - SLICES!!

● Bright Future

The Cluster

● replication factor (rf)● read consistency (r)● write consistency (w)● clustering - shard on

partition key

The One Ring

Storage - Vnodes

Data Model

● Wide rows

● Slices Queries

● Denormalization

● Index tables

CREATE TABLE email_app.emails ( user_id text, subject text, to_add text, cc text, body text, PRIMARY KEY(user_id));

Data Model - Simple Key

ROW KEY

Data Model - Simple InsertsINSERT INTO email_app.emails (user_id, subject, to_add, cc, body) VALUES (‘111’, ‘party’, ‘cat@b.com‘, ‘hippo@b.com‘, ‘at my place’);

INSERT INTO email_app.emails (user_id, subject, to_add, cc, body) VALUES (‘999’, ‘wat‘, ‘horse@b.com‘, ‘giraffe@b.com‘, ‘is going on?’);

Data Model Simple Inserts Result

Select * from email_app.emails;

111subject to_add cc body

wat horse@ giraffe@ is going on999

subject to_add cc body

party cat@ hippo@ at my place

Mental Model - Nested Hash

111

to cc bodyColumn Values

Row Keys 999

subject to cc bodysubject

INSERT INTO email_app.emails (user_id, subject, to_add, cc, body) VALUES (‘111’, ‘party’, ‘cat@b.com‘, ‘hippo@b.com‘, ‘at my place’);

Data Model - Simple Insert - Again

111 subject to_add cc body

party cat@ hippo@ at my place

subject to_add cc body

wat horse@ giraffe@ Is going on?999IDEMPOTENT

CREATE TABLE email_app.emails ( user_id text, subject text, to_add text, cc text, body text, PRIMARY KEY(user_id, subject));

Data Model - Composite Key 1

ROW KEY CLUSTERING KEY

INSERT INTO email_app.emails (user_id, subject, to_add, cc, body) VALUES (‘111’, ‘party‘, ‘cat@b.com‘, ‘hippo@b.com‘, ‘at my place’);

Data Model - Composite Insert 1

Same as Before. Right???

Data Model Composite Insert Result

Select * from emails WHERE user_id = 111;

111 party|to_ad party|cc party|body

cat@ hippo@ At my place

Subject

Mental Model - Nested Hash

111

to_add cc bodyColumn Values

Row Key

partyClustering Column

user_id

subject

INSERT INTO email_app.emails (user_id, subject, to_add, cc, body) VALUES (‘111’, ’swim’, ‘cat@b.com‘, ‘hippo@b.com‘, ‘in the pool’);

Data Model - Composite Insert 2

Composite Insert 2 Result

Select * from emails WHERE user_id = ‘111’;

111 party|to_add party|cc party|body

cat@ hippo@ at my place

Subject

swim|to_add swim|cc swim|body

cat@ hippo@b in the pool

Sorted by clustering column - “subject”

Mental Model - Nested Sorted Hash

111

party

to cc body

Clustering Column

Column Values

Row Key

swim

to cc body

subject

user_id

Why sorted?

SELECT * FROM emails WHERE user_id = '111' AND (subject) >= ('s') AND (subject) < (‘t’);

111 party|to_add party|cc party|body

cat@ giraffe@ At my place

SLICE QUERIES!!

swim|to_add swim|cc swim|body

cat@ hippo@b in the pool

CREATE TABLE email_app.emails ( user_id text, subject text, to_add text, cc text, body text, PRIMARY KEY((user_id, subject), to_add));

DM - Compound Composite Key

ROW KEY CLUSTERING KEY

INSERT INTO email_app.emails (user_id, subject, to_add, cc, body) VALUES (‘111’, ‘wat‘, ‘horse@b.com‘, ‘giraffe@b.com‘, ‘is going on?’);

INSERT INTO email_app.emails (user_id, subject, to_add, cc, body) VALUES (‘111’, ‘party‘, ‘cat@b.com‘, ‘hippo@b.com‘, ‘at my place’);

Composite / Compound Inserts

Composite Insert 2 Result

SELECT * FROM emails WHERE user_id = ‘111’AND subject = ‘party’;

111:partycat@|cc cat@|body

hippo@ At my place

SELECT * FROM emails WHERE user_id = ‘111’;

to_add

Data Model - Composite Insert 1

SELECT * FROM emails WHERE user_id = ‘111’ AND subject = ‘party’;

111:partycat@|cc cat@...|body

giraffe@ At my place

dog@|cc dog@|body

hippo@b all the time

Sorting / slice on - “to_add”

INSERT INTO email_app.emails (user_id, subject, to_add, cc, body) VALUES (‘111’, ‘party‘, ‘dog@b.com‘, ‘hippo@b.com‘, ‘all the time’);

to_add

CREATE TABLE email_app.emails ( user_id text, subject text, to_add text, cc text, body text, PRIMARY KEY((user_id, subject), to_add, cc));

DM - Compound Composite Key 2

ROW KEY CLUSTERING KEYS

Composite / Clustered InsertsINSERT INTO email_app.emails (user_id, subject, to_add, cc, body) VALUES (‘111’, ‘party‘, ‘dog@b.com‘, ‘hippo@b.com‘, ‘all the time);

INSERT INTO email_app.emails (user_id, subject, to_add, cc, body) VALUES (‘111’, ‘party‘, ‘cat@b.com‘, ‘hippo@b.com‘, ‘At my place’);

INSERT INTO email_app.emails (user_id, subject, to_add, cc, body) VALUES (‘111’, ‘party‘, ‘cat@b.com‘, ‘mouse@b.com‘, ‘At my place’);

DM - Composite / Clustered InsertsSELECT * FROM emails WHERE user_id = ‘111’ AND subject = ‘party’;

111|partycat@|hippo@|body cat@|mouse@|body

at my place at my place

dog@|hippo@|body

all the time

Slice on (to_add) OR (to_add, cc)

Mental Model - Nested Sorted Hash

111|party

cat dog

hippo mouse hippo

body body body

Clustering Columns

Column Values

Row Key

to_add

cc

user_id +subject

Part 2 / 8 of this 7 hour talk

● Denormalization

● Index Column Families

● Cassandra Internals (memtables, SSTables, compaction, repair)

Part 8 / 8: The Future

● Continually improving● More and more adoption● Awesome projects● http://www.datastax.

com/documentation/cassandra/2.0/pdf/cassandra20.pdf

● http://planetcassandra.org/