默认情况下，Pulsar主题在单个broker上运行。 Using only a single broker limits a topic’s maximum throughput. Partitioned topics are a special type of topic that can span multiple brokers and thus allow for much higher throughput. 有关分区主题如何工作，请参见 分区主题的概念。

You can publish to partitioned topics using Pulsar client libraries and you can create and manage partitioned topics using Pulsar admin API.

Publish to partitioned topics

When publishing to partitioned topics, you do not need to explicitly specify a routing mode when you create a new producer. If you do not specify a routing mode, the round robin route mode is used. Take Java as an example.

在Java客户端中将消息发布到分区主题，和发布到普通主题非常类似。 不同之处在于您需要指定一个消息路器(从已有的路由器中选择一个或实现一个自定义的路由器)。

Routing mode

You can specify the routing mode in the ProducerConfiguration object that you use to configure your producer. Three options are available:

• SinglePartition
• RoundRobinPartition
• CustomPartition

The following is an example:

String pulsarBrokerRootUrl = "pulsar://localhost:6650";
String topic = "persistent://my-tenant/my-namespace/my-topic";
PulsarClient pulsarClient = PulsarClient.builder().serviceUrl(pulsarBrokerRootUrl).build();
Producer<byte[]> producer = pulsarClient.newProducer()
        .topic(topic)
        .messageRoutingMode(MessageRoutingMode.SinglePartition)
        .create();
producer.send("Partitioned topic message".getBytes());

Custom message router

要使用自定义消息路由器，您需要提供MessageRouter 接口的实现，该接口只有一个choosePartition方法：

public interface MessageRouter extends Serializable {
    int choosePartition(Message msg);
}

The following router routes every message to partition 10:

public class AlwaysTenRouter implements MessageRouter {
    public int choosePartition(Message msg) {
        return 10;
    }
}

有了这个实现，你可以这样发送消息:

String pulsarBrokerRootUrl = "pulsar://localhost:6650";
String topic = "persistent://my-tenant/my-cluster-my-namespace/my-topic";
PulsarClient pulsarClient = PulsarClient.builder().serviceUrl(pulsarBrokerRootUrl).build();
Producer<byte[]> producer = pulsarClient.newProducer()
        .topic(topic)
        .messageRouter(new AlwaysTenRouter())
        .create();
producer.send("Partitioned topic message".getBytes());

How to choose partitions when using a key

If a message has a key, it supersedes the round robin routing policy. The following example illustrates how to choose partition when you use a key.

// If the message has a key, it supersedes the round robin routing policy
        if (msg.hasKey()) {
            return signSafeMod(hash.makeHash(msg.getKey()), topicMetadata.numPartitions());
        }
        if (isBatchingEnabled) { // if batching is enabled, choose partition on `partitionSwitchMs` boundary.
            long currentMs = clock.millis();
            return signSafeMod(currentMs / partitionSwitchMs + startPtnIdx, topicMetadata.numPartitions());
        } else {
            return signSafeMod(PARTITION_INDEX_UPDATER.getAndIncrement(this), topicMetadata.numPartitions());
        }

Manage partitioned topics

You can use Pulsar admin API to create and manage partitioned topics.