Cassandra NoSQL Tutorial

Getting to know
by Michelle Darling
mdarlingcmt@gmail.com
August 2013

Agenda:
● What is Cassandra?
● Installation, CQL3
● Data Modelling
● Summary
Only 15 min to cover these, so
please hold questions til the
end, or email me :-) and I’ll
summarize Q&A for everyone.
Unfortunately, no time for:
● DB Admin
○ Detailed Architecture
○ Partitioning /
Consistent Hashing
○ Consistency Tuning
○ Data Distribution &
Replication
○ System Tables
● App Development
○ Using Python, Ruby etc
to access Cassandra
○ Using Hadoop to
stream data into
Cassandra

What is Cassandra?
“Fortuneteller of Doom”
from Greek Mythology. Tried to
warn others about future disasters,
but no one listened. Unfortunately,
she was 100% accurate.
NoSQL Distributed DB
● Consistency - A__ID
● Availability - High
● Point of Failure - none
● Good for Event
Tracking & Analysis
○ Time series data
○ Sensor device data
○ Social media analytics
○ Risk Analysis
○ Failure Prediction
Rackspace: “Which servers
are under heavy load
and are about to crash?”

The Evolution of Cassandra
2008: Open-Source Release / 2013: Enterprise & Community Editions
Data Model
● Wide rows, sparse arrays
● High performance through very
fast write throughput.
Infrastructure
● Peer-Peer Gossip
● Key-Value Pairs
● Tunable Consistency
2006
2005
● Originally for Inbox Search
● But now used for Instagram

Other NoSQL vs. Cassandra
NoSQL Taxonomy:
● Key-Value Pairs
○ Dynamo, Riak, Redis
● Column-Based
○ BigTable, HBase,
Cassandra
● Document-Based
○ MongoDB, Couchbase
● Graph
○ Neo4J
Big Data Capable
C* Differentiators:
● Production-proven at
Netflix, eBay, Twitter,
20 of Fortune 100
● “Clear Winner” in
Scalability,
Performance,
Availability
-- DataStax

Architecture
● Cluster (ring)
● Nodes (circles)
● Peer-to-Peer Model
● Gossip Protocol
Partitioner:
Consistent Hashing

Netflix
Streaming Video
● Personalized
Recommendations per
family member
● Built on Amazon Web
Services (AWS) +
Cassandra

Cloud installation using
● Amazon Web Services (AWS)
● Elastic Compute Cloud (EC2)
○ Free for the 1st year! Then pay only for what you use.
○ Sign up for AWS EC2 account: Big Data University Video 4:34 minutes,
● Amazon Machine Image (AMI)
○ Preconfigured installation template
○ Choose: “DataStax AMI for Cassandra
Community Edition”
○ Follow these *very good* step-by-step
instructions from DataStax.
○ AMIs also available for CouchBase, MongoDB
(make sure you pick the free tier community versions to avoid
monthly charge$$!!!).

DataStax AMI Setup
--clustername Michelle
--totalnodes 1
--version community

“Roll your Own” Installation
DataStax Community Edition
● Install instructions
For Linux, Windows,
MacOS:
http://www.datastax.com/2012/01/getting-
started-with-cassandra
● Video: “Set up a 4-
node Cassandra
cluster in under 2
minutes”
http://www.screenr.com/5G6

Invoke CQLSH, CREATE KEYSPACE
./bin/cqlsh
cqlsh> CREATE KEYSPACE big_data
… with strategy_class = ‘org.apache.cassandra.
locator.SimpleStrategy’
… with strategy_options:replication_factor=‘1’;
cqlsh> use big_data;
cqlsh:big_data>

Tip: Skip Thrift -- use CQL3
Thrift RPC
// Your Column
Column col = new Column(ByteBuffer.wrap("name".
getBytes()));
col.setValue(ByteBuffer.wrap("value".getBytes()));
col.setTimestamp(System.currentTimeMillis());
// Don't ask
ColumnOrSuperColumn cosc = new ColumnOrSuperColumn();
cosc.setColumn(col);
// Prepare to be amazed
Mutation mutation = new Mutation();
mutation.setColumnOrSuperColumn(cosc);
List<Mutation> mutations = new ArrayList<Mutation>();
mutations.add(mutation);
Map mutations_map = new HashMap<ByteBuffer, Map<String,
List<Mutation>>>();
Map cf_map = new HashMap<String, List<Mutation>>();
cf_map.set("Standard1", mutations);
mutations_map.put(ByteBuffer.wrap("key".getBytes()),
cf_map);
cassandra.batch_mutate(mutations_map,
consistency_level);
CQL3
- Uses cqlsh
- “SQL-like” language
- Runs on top of Thrift RPC
- Much more user-friendly.
Thrift code on left
equals this in CQL3:
INSERT INTO (id, name)
VALUES ('key',
'value');

CREATE TABLE
cqlsh:big_data> create table user_tags (
… user_id varchar,
… tag varchar,
… value counter,
… primary key (user_id, tag)
…):
● TABLE user_tags: “How many times has a user
mentioned a hashtag?”
● COUNTER datatype - Computes & stores counter value
at the time data is written. This optimizes query
performance.

UPDATE TABLE
SELECT FROM TABLE
cqlsh:big_data> UPDATE user_tags SET
value=value+1 WHERE user_id = ‘paul’ AND tag =
‘cassandra’
cqlsh:big_data> SELECT * FROM user_tags
user_id | tag | value
--------+-----------+----------
paul | cassandra | 1

DATA MODELING
A Major Paradigm Shift!
RDBMS Cassandra
Structured Data, Fixed Schema Unstructured Data, Flexible Schema
“Array of Arrays”
2D: ROW x COLUMN
“Nested Key-Value Pairs”
3D: ROW Key x COLUMN key x COLUMN values
DATABASE KEYSPACE
TABLE TABLE a.k.a COLUMN FAMILY
ROW ROW a.k.a PARTITION. Unit of replication.
COLUMN COLUMN [Name, Value, Timestamp]. a.k.a CLUSTER. Unit
of storage. Up to 2 billion columns per row.
FOREIGN KEYS, JOINS,
ACID Consistency
Referential Integrity not enforced, so A_CID.
BUT relationships represented using COLLECTIONS.

Cassandra
3D+: Nested Objects
RDBMS
2D: Rows
x columns

Example:
“Twissandra” Web App
Twitter-Inspired
sample application
written in Python +
Cassandra.
● Play with the app:
twissandra.com
● Examine & learn
from the code on
GitHub.
Features/Queries:
● Sign In, Sign Up
● Post Tweet
● Userline (User’s tweets)
● Timeline (All tweets)
● Following (Users being
followed by user)
● Followers (Users
following this user)

Twissandra - RDBMS Version
Entities
● USER, TWEET
● FOLLOWER, FOLLOWING
● FRIENDS
Relationships:
● USER has many TWEETs.
● USER is a FOLLOWER of many
USERs.
● Many USERs are FOLLOWING
USER.

Twissandra - Cassandra Version
Tip: Model tables to mirror queries.
TABLES or CFs
● TWEET
● USER, USERNAME
● FOLLOWERS, FOLLOWING
● USERLINE, TIMELINE
Notes:
● Extra tables mirror queries.
● Denormalized tables are
“pre-formed”for faster
performance.

TABLE
Tip: Remember,
Skip Thrift -- use CQL3

What does C* data look like?
TABLE Userline
“List all of user’s Tweets”
*************
Row Key: user_id
Columns
● Column Key: tweet_id
● “at” Timestamp
● TTL (Time to Live) -
seconds til expiration
date.
*************

Cassandra Data Model = LEGOs?
FlexibleSchema

Summary:
● Go straight from SQL
to CQL3; skip Thrift, Column
Families, SuperColumns, etc
● Denormalize tables to
mirror important queries.
Roughly 1 table per impt query.
● Choose wisely:
○ Partition Keys
○ Cluster Keys
○ Indexes
○ TTL
○ Counters
○ Collections
See DataStax Music Service
Example
● Consider hybrid
approach:
○ 20% - RDBMS for highly
structured, OLTP, ACID
requirements.
○ 80% - Scale Cassandra to
handle the rest of data.
Remember:
● Cheap: storage,
servers, OpenSource
software.
● Precious: User AND
Developer Happiness.

Resources
C* Summit 2013:
● Slides
● Cassandra at eBay Scale (slides)
● Data Modelers Still Have Jobs -
Adjusting For the NoSQL
Environment (Slides)
● Real-time Analytics using
Cassandra, Spark and Shark
slides
● Cassandra By Example: Data
Modelling with CQL3 Slides
● DATASTAX C*OLLEGE CREDIT:
DATA MODELLING FOR APACHE
CASSANDRA slides
I wish I found these 1st:
● How do I Cassandra?
slides
● Mobile version of
DataStax web docs
(link)

Cassandra NoSQL Tutorial

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