Geneva JUG - Cassandra for Java Developers

Cassandra for Java DevelopersDataStax Driver & DevCenter

Michaël FiguièreDrivers & Developer Tools Architect

© 2014 DataStax, All Rights Reserved.

Client / Server Communication

2

Client

Client

Client

Client

Node

Node Replica

Replica

ReplicaNode

Coordinator node:Forwards all R/W requeststo corresponding replicas


Request Pipelining

3

Client

WithoutRequest Pipelining

Cassandra

Client CassandraWith

Request Pipelining


Notifications

4

Client

WithoutNotifications

WithNotifications

NodeNode

Node

Client

NodeNode

Node


Asynchronous Driver Architecture

5

ClientThread

Node

Node

Node

ClientThread

ClientThread

Node

Driver


Asynchronous Driver Architecture

6

ClientThread

Node

Node

Node

ClientThread

ClientThread

Node

6

23

45

1

Driver


Failover

7

ClientThread

Node

Node

Node

ClientThread

ClientThread

Node

7

2

4

531

Driver

6


Java Driver Highlights

• Reference implementation• Asynchronous architecture based on Netty• Prepared Statements Support• Automatic Failover• Node Discovery• Tunable Load Balancing

• Round Robin, Multi Data Centers, Latency Awareness, Replica Awareness

• Cassandra Tracing Support• Compression & SSL

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© 2014 DataStax, All Rights Reserved. 9

DataStax Driver in Practice

<dependency> <groupId>com.datastax.cassandra</groupId> <artifactId>cassandra-‐driver-‐core</artifactId> <version>2.1.0</version>

</dependency>

Available in Maven Central. Depends on Netty, Guava, Metrics

Supports Apache Cassandra 1.2 to 2.1


Connect and Write

Cluster cluster = Cluster.builder() .addContactPoints("127.0.0.1", “127.0.0.2") .build();

Session session = cluster.connect(“my_keyspace");

session.execute( "INSERT INTO user (user_id, name, email) VALUES (12345, 'johndoe', '[email protected]')");

The rest of the nodes will be discovered by the driver

A keyspace is just like a schema in the SQL world


Read

ResultSet resultSet = session.execute("SELECT * FROM user");

List<Row> rows = resultSet.all(); for (Row row : rows) {

String userId = row.getString("user_id"); String name = row.getString("name"); String email = row.getString("email");}

Actually ResultSet also implements Iterable<Row>

Session is a thread safe object. A singleton should be instantiated at startup


Write with Prepared Statements

PreparedStatement insertUser = session.prepare( "INSERT INTO user (user_id, name, email) VALUES (?, ?, ?)");

BoundStatement statement = insertUser .bind(12345, "johndoe", "[email protected]") .setConsistencyLevel(ConsistencyLevel.QUORUM);

session.execute(statement);

Parameters can be named as well

PreparedStatement objects are also threadsafe, just create a singleton at startup

BoundStatement is a stateful, NON threadsafe object

Consistency Level can be set for each statement


Asynchronous Read

ResultSetFuture future = session.executeAsync("SELECT * FROM user");

ResultSet resultSet = future.get();

List<Row> rows = resultSet.all(); for (Row row : rows) {

String userId = row.getString("user_id"); String name = row.getString("name"); String email = row.getString("email");}

Will NOT block unless all the connections are busy

Will block until less all the connections are busy


Asynchronous Read with Callbacks

ResultSetFuture future = session.executeAsync("SELECT * FROM user");

future.addListener(new Runnable() { public void run() { // Process the results here }}, executor);

ResultSetFuture implements Guava’s ListenableFuture

executor = Executors .newCachedThreadPool();

executor = MoreExecutors .sameThreadExecutor();

Only if your listener code is trivial and non blocking as it’ll be executed in the IO Thread

…Or any thread pool that you prefer


Query Builder

import staticcom.datastax.driver.core.querybuilder.QueryBuilder.*;

Statement selectAll = select().all().from("user").where(eq("user_id", userId));

session.execute(selectAll);

Statement insert = insertInto("user") .value("user_id", 2) .value("name", "johndoe") .value("email", "[email protected]");

session.execute(insert);

import static of QueryBuilder is required in order to use the DSL


Object Mapper

• Avoid boilerplate for common use cases

• Map Objects to Statements and ResultSets to Objects

• Do NOT hide Cassandra from the developer

• No “clever tricks” à la Hibernate

• Not JPA compatible, but JPA-ish API

16


Object Mapper in Practice

<dependency> <groupId>com.datastax.cassandra</groupId> <artifactId>cassandra-‐driver-‐mapping</artifactId> <version>2.1.0</version>

</dependency>

Additional artifact for object mapping

Available from Driver 2.1.0


Basic Object Mapping

CREATE TYPE address ( street text, city text, zip int ); CREATE TABLE users ( email text PRIMARY KEY, address address );

@UDT(keyspace = "ks", name = "address") public class Address { private String street; private String city; private int zip; // getters and setters omitted... } @Table(keyspace = "ks", name = "users") public class User { @PartitionKey private String email; private Address address; // getters and setters omitted... }


Basic Object Mapping

MappingManager manager = new MappingManager(session);

Mapper mapper = manager.mapper(User.class); UserProfile myProfile = mapper.get("[email protected]");

ListenableFuture saveFuture = mapper.saveAsync(anotherProfile);

mapper.delete("[email protected]");

Mapper, just like Session, is a thread-safe object. Create a singleton at startup.

get() returns a mapped row for the given Primary Key

ListenableFuture from Guava. Completed when the write is acknowledged.

mailto:[email protected]


Accessors

UserAccessor accessor = manager.createAccessor(UserAccessor.class); Result<User> users = accessor.firstN(10);

for (User user : users) { System.out.println( profile.getAddress().getZip() ); }

Result is like ResultSet but specialized for a mapped class…

…so we iterate over it just like we would with a ResultSet

@Accessor interface UserAccessor { @Query("SELECT * FROM user_profiles LIMIT :max") Result<User> firstN(@Param("max") int limit); }

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Geneva JUG - Cassandra for Java Developers

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