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Geneva JUG - Cassandra for Java Developers
This document discusses the DataStax Java driver and DevCenter tool for Cassandra. It provides an overview of client/server communication in Cassandra, including request pipelining and notifications. It then summarizes key aspects of the asynchronous Java driver architecture, including failover handling. The document demonstrates basic usage of the driver for connecting, reading, writing with prepared statements, and asynchronous reads. It also introduces the object mapping functionality for avoiding boilerplate code when mapping Cassandra rows to Java objects.
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Geneva JUG - Cassandra for Java Developers
- 1. Cassandra for JavaDevelopers DataStax Driver & DevCenter Michaël Figuière Drivers & Developer Tools Architect
- 2. Client / ServerCommunication © 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
- 3. Request Pipelining ©2014 DataStax, All Rights Reserved. 3 Client Without Request Pipelining Cassandra Client Cassandra With Request Pipelining
- 4. Notifications © 2014DataStax, All Rights Reserved. 4 Client Without Notifications With Notifications Node Node Node Client Node Node Node
- 5. Asynchronous Driver Architecture © 2014 DataStax, All Rights Reserved. 5 Client Thread Node Node Node Client Thread Client Thread Node Driver
- 6. Asynchronous Driver Architecture © 2014 DataStax, All Rights Reserved. 6 Client Thread Node Node Node Client Thread Client Thread Node 6 2 3 4 5 1 Driver
- 7. Failover © 2014DataStax, All Rights Reserved. 7 Client Thread Node Node Node Client Thread Client Thread Node 7 2 4 3 5 1 Driver 6
- 8. 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 © 2014 DataStax, All Rights Reserved. 8
- 9. DataStax Driver inPractice <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
- 10. 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 © 2014 DataStax, All Rights Reserved. 10
- 11. Read Session isa 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> © 2014 DataStax, All Rights Reserved. 11
- 12. Write with PreparedStatements 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 © 2014 DataStax, All Rights Reserved. 12
- 13. Asynchronous Read ResultSetFuturefuture = 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 © 2014 DataStax, All Rights Reserved. 13
- 14. Asynchronous Read withCallbacks 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 © 2014 DataStax, All Rights Reserved. 14
- 15. Query Builder importstatic 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); © 2014 DataStax, All Rights Reserved. 15
- 16. 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 © 2014 DataStax, All Rights Reserved. 16
- 17. Object Mapper inPractice <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 © 2014 DataStax, All Rights Reserved. 17
- 18. 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... } © 2014 DataStax, All Rights Reserved. 18
- 19. 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. © 2014 DataStax, All Rights Reserved. 19
- 20. 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 © 2014 DataStax, All Rights Reserved. 20
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- 22. We’re Hiring! github.com/datastax blog.datastax.com @mfiguiere