Geneva JUG - Cassandra for Java Developers

Cassandra for Java Developers
DataStax Driver & DevCenter
Michaël Figuière
Drivers & Developer Tools Architect

Client / Server Communication
© 2014 DataStax, All Rights Reserved.
2
Client
Client
Client
Client
Node
Node Replica
Replica
Replica
Node
Coordinator node:
Forwards all R/W requests
to corresponding replicas

Request Pipelining
3
Client
Without
Request Pipelining
Cassandra
Client Cassandra
With
Request Pipelining

Notifications
4
Client
Without
Notifications
With
Notifications
Node
Node
Node
Client
Node
Node
Node

Asynchronous Driver Architecture
5
Client
Thread
Node
Node
Node
Client
Thread
Client
Thread
Node
Driver

Asynchronous Driver Architecture
6
Client
Thread
Node
Node
Node
Client
Thread
Client
Thread
Node
6
2
3
4
5
1
Driver

Failover
7
Client
Thread
Node
Node
Node
Client
Thread
Client
Thread
Node
7
2
4
3 5 1
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
8

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
© 2014 DataStax, All Rights Reserved. 9

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', 'john@doe.com')"
);
The rest of the
nodes will be
discovered by
the driver
A keyspace is
just like a
schema in the
SQL world

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

Write with Prepared Statements
PreparedStatement objects
are also threadsafe, just create
a singleton at startup
PreparedStatement insertUser = session.prepare(
"INSERT INTO user (user_id, name, email)
VALUES (?, ?, ?)"
);
BoundStatement statement = insertUser
.bind(12345, "johndoe", "john@doe.com")
.setConsistencyLevel(ConsistencyLevel.QUORUM);
session.execute(statement);
Parameters can
be named as well
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 static of
QueryBuilder is required in
order to use the DSL
import static
com.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", "john@doe.com");
session.execute(insert);

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("xyz@example.com");
ListenableFuture
saveFuture
=
mapper.saveAsync(anotherProfile);
mapper.delete("xyz@example.com");
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.

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

We’re Hiring!
github.com/datastax
blog.datastax.com
@mfiguiere

Geneva JUG - Cassandra for Java Developers

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