Cassandra Driver Architecture and Libraries

1. Cassandra Drivers And Tools
DuyHai DOAN, Technical Advocate
@doanduyhai

2. Agenda!
@doanduyhai
2
Drivers
• architecture, policies, Java driver API
DevCenter (live coding demo!)
Cassandra Unit (+ live coding demo!)
Object Mapper module (+ live coding demo!)
Achilles Object Mapper (+ live coding demo!)

3. Cassandra Drivers Architecture!
Architecture!
Policies!
Java driver API!

4. Drivers list!
@doanduyhai
4
• Java
• C#
• Python
• Node.js
• Ruby (1.0.0.rc1)
• C++ (beta)
• ODBC (beta)
• Clojure (community)
• Go (community)
• PHP (to be announced)

5. Connection pooling!
@doanduyhai
5
n3
n2
n4
Driver
Pool1
Pool2
Pool3
Client
Thread1
Client
Thread2
Client
Thread3

6. Connection pooling!
@doanduyhai
6
n3
n2
n4
Driver
Pool1
Pool2
Pool3
Client
Thread1
Client
Thread2
Client
Thread3
1
2 3
4
5
6

7. Request Pipelining!
@doanduyhai
7
Client Cassandra

8. Request Pipelining!
@doanduyhai
8
Client Cassandra
StreamID
StreamID

9. Nodes Discovery!
@doanduyhai
9
n2
n3
n4
n5
n6
n7
n8
Control Connection
n1 Driver

10. Round Robin Load Balancing!
@doanduyhai
10
n2
n3
n4
n5
n6
n7
n8
n1 Client
1
2
3
4

11. DC Aware Load Balancing!
@doanduyhai
11
Client1 DC1
⤫
Client2 DC2

12. DC Aware Load Balancing!
@doanduyhai
12
⤫
Client1 DC1
Client2 DC2

13. Token Aware Load Balancing!
@doanduyhai
13
n2
n3
n4
n5
n6
n7
n8
1
n1 Client
2
3
⤫

14. Combining Load Balancing Policies!
Token Aware
Round Robin DC Aware Round Robin
@doanduyhai
14
extends
Load Balancing Policy
wraps
Default config

15. Automatic Failover!
@doanduyhai
15
n3
n2
n4
Driver
7 6
Pool1
4 5
Pool2
Pool3
Client
Thread
⤫
1
2
3
8

16. Other policies!
@doanduyhai
16
Retry policy
• write/read timeout
• node unavailable
Reconnection policy
• constant schedule
• exponential schedule

17. Statements!
@doanduyhai
17
Plain statement
• convenient, one-off query
• plain string ☞ parsing overhead
INSERT INTO user(login, name, age) VALUES(‘jdoe’, ‘John DOE’, 33)’;

18. Statements!
@doanduyhai
18
Prepared statements
• avoid parsing overhead
• query structure should be known ahead of time
• bound values
• named parameters
INSERT INTO user(login, name, age) VALUES(?, ?, ?)’;
INSERT INTO user(login, name, age) VALUES(:login, :name, :age)’;

19. Statements!
@doanduyhai
19
Parameterized statements
• same as plain statement
• pass bound values as bytes ☞ avoid ser/deser of values
INSERT INTO user(login, name, age) VALUES(?, ?, ?)’;

20. Java Driver!
@doanduyhai
20
Reference implementation
Base on asynchronous Netty library
Configurable policies
Query tracing support
Client-node compression & SSL

21. Maven dependency!
Available on Maven Central
@doanduyhai
21
<dependency>
<groupId>com.datastax.cassandra</groupId>
<artifactId>cassandra-driver-core</artifactId>
<version>2.1.3</version>
</dependency>
depends on Netty, Guava, Metrics

22. Connect and Write!
@doanduyhai
22
Cluster cluster = Cluster.builder()
.addContactPoints("127.0.0.1", “another-host").build();
seed nodes (IP or DNS name)
Session session = cluster.connect("my_keyspace");
session.execute("INSERT INTO user (user_id, name, email)
VALUES (12345, 'johndoe', 'john_doe@fiction.com’)");

23. Configuration!
@doanduyhai
23
Cluster cluster = Cluster.builder()
.addContactPoints("127.0.0.1", “another-host")
.withLoadBalancingPolicy(new DCAwareRoundRobinPolicy("DC1")
.withRetryPolicy(DowngradingConsistencyRetryPolicy.INSTANCE)
.withReconnectionPolicy(new ConstantReconnectionPolicy(1000))
.build();

24. Read!
@doanduyhai
24
ResultSet resultSet = session.execute("SELECT * FROM user");
List<Row> rows = resultSet.all();
for (Row row : rows) {
Long userId = row.getLong("user_id");
String name = row.getString("name");
String email = row.getString("email");
}
Stateless ☞ thread-safe

25. Asynchronous Read!
ResultSetFuture future = session.executeAsync("SELECT * FROM user");
ResultSet resultSet = future.get(); //blocking call
List<Row> rows = resultSet.all();
for (Row row : rows) {
Long userId = row.getLong("user_id");
String name = row.getString("name");
String email = row.getString("email");
}
@doanduyhai 25

26. Asynchronous Read with CallBack!
ResultSetFuture future = session.executeAsync("SELECT * FROM user");
future.addListener(new Runnable() {
public void run() {
// Process the results here
}
}, executor);
executor = Executors .newCachedThreadPool();
or
executor = Executors .sameThreadExecutor();
@doanduyhai 26

27. Query Builder!
Query query = QueryBuilder
.select()
.all()
.from( "my_keyspace", "user")
.where(eq("login", "jdoe"));
query.setConsistencyLevel(ConsistencyLevel.ONE);
ResultSet rs = session.execute(query);
@doanduyhai 27

28. Old manual paging!
@doanduyhai
28
Some time you need to fetch all table content
Manual paging:
SELECT * FROM users WHERE token(login) >= token(<last_fetched_login>)
LIMIT 100;

29. New automatic paging!
@doanduyhai
29
n2
n3
n4
n5
n6
n7
n8
Query
n1 Driver
Page 1 + paging state 1

30. New automatic paging!
@doanduyhai
30
n2
n3
n4
n5
n6
n7
n8
Query
n1 Driver
Page 2 + paging state 2

31. New automatic paging!
@doanduyhai
31
Paging state ≈ stateless cookie
Resilient to node failure

32. Paging during node failure!
@doanduyhai
32
n2
n3
n4
n5
n6
n7
n8
Query
n1 Driver
Page 1 + paging state 1

33. Paging during node failure!
@doanduyhai
33
n2
n3
n4
n5
n6
n7
n8
Query
n1 Driver
Page 2 + paging state 2
⤫

34. ! "
!
Q & R

35. Dev Center
Demo

36. Cassandra Unit!
@doanduyhai
36
• start an embedded Cassandra server
• useful for unit testing
• mature project, created at August 5th 2011
• designed around Thrift & Hector
• propose a JUnit rule for CQL

37. Cassandra Unit
Demo

38. Java Driver Object Mapper!
@doanduyhai
38
• simple mapper
• KISS
• annotations à-la JPA (but no JPA dependencies)
• templating system à-la Spring Data

39. Java Driver Object Mapper!
Mapping
@doanduyhai
39
@Table(keyspace = "mapper_module", name = "users")
public class User {
@PartitionKey
private String login;
private String name;
// getters and setters omitted...
}

40. Java Driver Object Mapper!
Usage
@doanduyhai
40
MappingManager manager = new MappingManager(session);
Mapper mapper = manager.mapper(User.class);
User user = mapper.get("jdoe@fiction.com");
mapper.saveAsync(new User("hsue@fiction.com"));
mapper.delete("jdoe@fiction.com");

41. Java Driver Object Mapper!
Accessors (SpringData template-like) definition
@doanduyhai
41
@Accessor
interface UserAccessor {
@Query("SELECT * FROM users LIMIT :max")
Result<User> firstNUsers(@Param("max") int limit);
}

42. Java Driver Object Mapper!
@doanduyhai
42
Accessors usage
UserAccessor accessor = manager.createAccessor(UserAccessor.class);
List<User> users = accessor.firstNUsers(10).all();
for (User user : users) {
System.out.println( profile.getAddress().getZip() );
}

43. Java Driver Object Mapper
Demo

44. Achilles!
@doanduyhai
44
Why ?
• started in late 2012, when mapper module did not exists
• more involved and more features than the mapper module
• different annotations set (may converge)

45. Achilles
Demo

46. Dirty Checking!
@doanduyhai
46
Dirty checking, why is it important ?
• 1 user ≈ 8 mutable fields
• × n denormalizations = n update combinations
• and not even counting multiple fields updates …

47. Dirty Checking!
@doanduyhai
47
• Are you going to manually generate n prepared statements for all
possible updates ?
• Or just use dynamic plain string statements and get some perf
penalty ?

48. Dirty Checking!
@doanduyhai
48
//No read-before-write
ContactEntity proxy = manager.forUpdate(ContactEntity.class, contactId);
proxy.setFirstName(…);
proxy.setLastName(…); //type-safe updates
proxy.setAddress(…);
manager.update(proxy);

49. Dirty Checking!
@doanduyhai
49
Proxy
Setters interception
DirtyMap
Empty
Entity
PrimaryKey

50. Dirty Checking!
@doanduyhai
50
• Dynamic statement generation
UPDATE contacts SET firstname=?, lastname=?,address=?
WHERE contact_id=?
prepared statements are cached, of course

51. Main API!
@doanduyhai
51
manager.insert(entity)
manager.update(entity)
manager.remove(entity)
manager.find(Entity.class, primaryKey)

52. Advanced Features!
@doanduyhai
52
Counter
Batch mode
Strategies (insert, naming)
Options
Asynchronous

53. Documentation!
@doanduyhai
53
Comprehensive Github WIKI
Twitter-clone demo app (demo.achilles.io)
Versioned documentation (HTML & PDF)
JavaDoc

54. RoadMap!
@doanduyhai
54
C* 2.1 user defined types (UDT)
Query-templates à-la Spring Data
Reactive ? (RxJava)
ElasticSearch integration (@olivierbourgain)

55. ! "
!
Q & R

56. Thank You
@doanduyhai
duy_hai.doan@datastax.com
https://academy.datastax.com/