This is an introductory presentation to Cassandra, the database of choice for high availability and insane scalability. I gave this talk at TheEdge conference.

1. #theedge2012
Practical Introduction
To
Sonia Margulis
@robosonia
March 2012

2. Your Application

3. Gone Viral

4. Best Hardware Money Can Buy

5. Improve Reads

6. Sharding RDBMS – A Nightmare

7. Cassandra’s Sweet Spot
Many Linear
concurrent Scalability
users
Distributed
High Volumes Inherently
of Operations Clustered

8. The Road to Mastership
Introduction
to Cassandra Introduction to
Cassandra
Data
Running a Model
Server
Modeling
Data
Communicating
with the Server
Growing
a Cluster

9. A non-relational database
Values availability
Scales out, not up
Open source
Active community

10. Always
Available

11. Who Uses It?

12. Use Case: Social & Timelines

13. Use Case: Statistics & Logs
Logs by Rick Payette

14. The Road to Mastership
Introduction
to Cassandra
Running a Server
Data
Running a Model
Server
Modeling
Data
Communicating
with the Server
Growing
a Cluster

15. The Cassandra Project
» Project
» Runs on:
» Apache License
» Current release: 1.0.8
You are
here
sonia@hiro:~/apache-cassandra-1.0.8$

16. Running a Server
sonia@hiro:~/apache-cassandra-1.0.8$
bin/cassandra -f
....
Now serving reads.
localhost/127.0.0.1:9160

17. Connecting to Our Server
Cassandra command line interface (CLI) tool
sonia@hiro:~/apache-cassandra-1.0.8$
bin/cassandra-cli –host 127.0.0.1 –port 9160
Connected to: “Test Cluster” on
localhost/9160
Welcome to Cassandra CLI version 1.0.8

18. Creating a Keyspace
Cassandra’s equivalent to RDBMSs database
[default@unknown] create keyspace demo;
Lets start using it
[default@unknown] use demo;
[default@demo]

19. Creating a Column Family
A column family holds data, much like a table in
RDBMS.
[default@demo] create column family user;
Start adding data
[default@demo] set user[1][a]=utf8(„foo‟);
[default@demo] set user[2][b]=utf8(„bar‟);
[default@demo] set user[2][c]=utf8(„test‟);

20. Retrieving Data
Retrieving columns by user key
[default@demo] get user[2];
(column=b, value=bar)
(column=c, value=test)
Returned 2 results.

21. The Road to Mastership
Introduction
to Cassandra
Data Model
Data
Running a Model
Server
Modeling
Data
Communicating
with the Server
Growing
a Cluster

22. Column
Column
Name
Value

23. Column
name
Peter Parker
1
name Peter Parker

24. Row
icon name residence
spiderman
Peter Parker New York

25. Row
Columns
Row Id
icon name residence
spiderman
Peter Parker New York
1 2
spiderman name Peter Parker

26. Column Family
spider- icon name residence
man Peter P New York
icon name residence
batman
Bruce W Gotham
icon name residence
hulk
Bruce B New York

27. Column Family
spider- icon name residence
man Peter P New York
icon name residence
batman
set user[„spiderman‟][„name‟] W „Peter Parker‟
Bruce = Gotham
icon name residence
hulk Value
Column
Bruce B New York
Row id name
Column
Family

28. The Allies Column Family
Robin Alfred
batman
spider- Iceman Firestar Iron Man Storm
man

29. Published Issues Column Family
~2600 columns
spider- 1/8/1962
man ###
... 1/3/2012 8/3/2012
### ###
batman 1/5/1939
###
... 2/3/2012 9/3/2012
### ###
~3800 columns

30. Model Flexibility
Flexible
Data Model
Image: photostock / FreeDigitalPhotos.net

31. Keyspace
» Like RDBMS database
» A container for column families
[default@unknown] create keyspace demo;
» One keyspace per application, in most cases

32. Expiring Columns – TTL
icon name passwd_ residence
spider- reminder
man Peter P abcd New York
set users[„spiredman‟][„passwd_reminder‟] =
„abcd‟ with ttl = 7200;
7200s = 2 hours

33. Distributed Counters
javaedge speakers sessions
.com 1035 3402
incr page_views[„javaedge.com‟][„speakers‟] by 1
get page_views[„javaedge.com‟][„speakers‟]

34. The Road to Mastership
Introduction
to Cassandra Communication with
the Server: Clients
Data
Running a Model
Server
Modeling
Data
Communicating
with the Server
Growing
a Cluster

35. Cassandra Query Language
» Looks a lot like SQL
INSERT INTO users (KEY, name, universe)
VALUES (hulk, Bruce, marvel)
» Mostly valid SQL
SELECT name, universe
FROM users
WHERE KEY = „hulk‟

36. Advantages of using CQL
» Run ad-hoc queries
» Very familiar, easier to use
» Stable interface
▪ For library developers
▪ For users

37. CQL Example
SELECT name, residence FROM users
SELECT 01/1/2011 .. 1/1/2012
FROM published_issues
WHERE KEY = „spiderman‟
SELECT FIRST 5
FROM allies
WHERE KEY = „spiderman‟

38. CQL Example
SELECT name, residence FROM users
SELECT 01/1/2011 .. 1/1/2012
FROM published_issues
WHERE KEY = „spiderman‟
SELECT FIRST 5
FROM allies
WHERE KEY = „spiderman‟

39. CQL Example
SELECT name, residence FROM users
SELECT 01/1/2011 .. 1/1/2012
FROM published_issues
WHERE KEY = „spiderman‟
SELECT FIRST 5
FROM allies
WHERE KEY = „spiderman‟

40. Cassandra JDBC Driver
import java.sql.*;
Class.forName(
"org.apache.cassandra.cql.jdbc.CassandraDriver");
Connection con = DriverManager.getConnection(
"jdbc:cassandra://localhost:9160/keyspace");

41. Cassandra JDBC Driver
Statement stmt = con.createStatement();
ResultSet rs = stmt.executeQuery(
“SELECT name, residence
FROM users
WHERE KEY ='" + key + "'");

42. Cassandra JDBC Driver
JDBC

43. Hector
SliceQuery<...> query =
HFactory.createSliceQuery(keyspace, ...);
query.setRange(startDate, endDate, false, 100)
.setColumnFamily("published_issues")
.setKey("spiderman");
QueryResult<ColumnSlice<Date, String>> result =
query.execute();

44. Hector: Advanced Features
» Failover support
» Connection pooling
» Load balancing
» JMX counters
» Object mapper

45. Maven plugin
mvn cassandra:start
Run your tests
mvn cassandra:cql-exec
mvn cassandra:stop

46. The Road to Mastership
Introduction
to Cassandra
Modeling Data
Data
Running a Model
Server
Modeling
Data
Communicating
with the Server
Growing
a Cluster

47. Queries First
» Use the same Column Family for data that
should be fetched together
▪ Reduces IO
» Consider filtering and ordering

48. Denormalize
» Less seeks - faster reads
» Storing redundant data
▪ Manually handling data integrity
» Disk space is cheaper than seek time

49. Secondary Index
» Requirement:
Find all superheroes that live in New York
icon name residence
spiderman
Peter Parker New York

50. Secondary Index
» Requirement:
Find all superheroes that live in New York
icon name residence
spiderman
Peter Parker New York
create column family users
... and column_metadata=
[{column_name: residence, index_type: KEYS}];
» Good nameindexes with low cardinality
SELECT for
FROM users
WHERE residence = „New York‟

51. Manually Managed Index
» Requirement:
Find a superhero by name

52. Manually Managed Index
» Requirement:
Find a superhero by name
hulk batman
Bruce
Search Keys in
term users CF
spiderman
Peter
» Manually maintain an inverted index

53. Bucketing
hulk_jan 1/1/2012 2/1/2012 4/1/2012
_2012 Issue-1 Issue-2 Issue-3
All
issues
hulk_feb 2/2/2012 28/2/2012 29/2/2012
_2012 Issue-4 Issue-5 Issue-6
By month

54. The Road to Mastership
Introduction
to Cassandra
Cassandra Cluster
Data
Running a Model
Server
Modeling
Data
Communicating
with the Server
Growing
a Cluster

55. Virtual Ring
10
90 40
75 60

56. Node Token
10
Node Keys
90 40
10 91-10
40 11-40
60 41-60
75 61-75
90 76-90
75 60

57. Node Token
hulk
MD5’(hulk) = 20 10
90 40
75 60

58. Node Token
MD5’(hulk) = 20 10 hulk
90 40
75 60

59. Node Token
10 hulk
thor 40
MD5’(thor) = 42 90
75 60

60. Node Token
10 hulk
MD5’(thor) = 42 90 40
thor
75 60

61. Inter-Node Communication
10
90 40
» Gossip
» Failure
Detection
75 60

62. Fault Tolerance
» Replication factor
» Hinted Handoff
10 hulk
90 40
75 60 thor

63. Replication Factor
» Replication factor
» Hinted Handoff
10 hulk
thor 90 Replication
40
factor = 3
hulk hulk
thor 75 60 thor

64. Fault Tolerance
» Replication factor
» Hinted Handoff
10
90 40
75 60

65. Hinted Handoff
» Replication factor
» Hinted Handoff
10
90 40
75 60

66. Hinted Handoff
» Replication factor
» Hinted Handoff
10
90 40
75 60

67. Client Requests
Coordinator
10
Write Request
90
75 60

68. Consistency Level
Consistency
level = ONE
10
Write Request
90
75 60

69. Consistency Level
Consistency
level = ALL
10
Write Request
90
75 60

70. The Road to Mastership
Introduction
to Cassandra
Summary
Data
Running a Model
Server
Modeling
Data
Communicating
with the Server
Growing
a Cluster

72. Where Do You Sign?
» Cassandra
▪ http://cassandra.apache.com
▪ http://www.datastax.com/
• Docs, tutorials & videos
▪ IRC: #cassandra on freenode
» Hector
▪ https://github.com/rantav/hector
▪ https://github.com/zznate/hector-examples