YaJug - Cassandra for Java Developers
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This document summarizes a presentation on Cassandra for Java developers. It discusses client/server communication in Cassandra, including how requests are forwarded to replicas. It also covers request pipelining, notifications, the asynchronous driver architecture, failover handling, features of the Java driver like prepared statements and load balancing, and how to connect to Cassandra and perform reads and writes using the driver. Finally, it discusses the object mapper for mapping between Cassandra and Java objects.
YaJug - Cassandra for Java Developers
- 1. Cassandra for Java Developers DataStax Driver & DevCenter Michaël Figuière Drivers & Developer Tools Architect
- 2. 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
- 3. Request Pipelining © 2014 DataStax, All Rights Reserved. 3 Client Without Request Pipelining Cassandra Client Cassandra With Request Pipelining
- 4. Notifications © 2014 DataStax, 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 © 2014 DataStax, 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, Latency Awareness, Multi Data Centers, Replica Awareness • Cassandra Tracing Support • Compression & SSL © 2014 DataStax, All Rights Reserved. 8
- 9. DataCenter Aware Balancing © 2014 DataStax, All Rights Reserved. 9 Node Node Client Node Node Datacenter B Node Node Client Client Client Client Client Datacenter A Local nodes are queried first, if non are available, the request could be sent to a remote node.
- 10. Token Aware Balancing © 2014 DataStax, All Rights Reserved. Nodes that own a Replica of the PK being read or written by the query will be contacted first. 10 Node Node Replica Node Client Replica Replica Partition Key will be inferred from Prepared Statements metadata
- 11. 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. 11
- 12. Connect and Write Cluster cluster = Cluster.builder() .addContactPoints("10.1.2.5", "cassandra_node3") .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 © 2014 DataStax, All Rights Reserved. 12
- 13. Read ResultSet resultSet = session.execute( Session is a thread safe object. A singleton should be instantiated at startup "SELECT * FROM user WHERE user_id IN (1,8,13)" ); 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. 13
- 14. 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", "[email protected]") .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. 14
- 15. Asynchronous Read ResultSetFuture future = session.executeAsync( "SELECT * FROM user WHERE user_id IN (1,2,3)" ); 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. Returns immediately Will block until less all the connections are busy © 2014 DataStax, All Rights Reserved. 15
- 16. Asynchronous Read with Callbacks ResultSetFuture future = session.executeAsync( "SELECT * FROM user WHERE user_id IN (1,2,3)" ); 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. 16
- 17. 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", "[email protected]"); session.execute(insert); © 2014 DataStax, All Rights Reserved. 17
- 18. 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. 18
- 19. 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 © 2014 DataStax, All Rights Reserved. 19
- 20. 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. 20
- 21. 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. © 2014 DataStax, All Rights Reserved. 21
- 22. 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. 22
- 24. We’re Hiring! github.com/datastax blog.datastax.com @mfiguiere …seriously I really mean it, so if you’re passionated about beautiful technology feel free to talk to me! Work remotely from anywhere in Europe, even Luxembourg…