路由元信息

NameServer路由实现类：org.apache.rocketmq.namesrv.routeinfo.RouteInfoManager，在了解路由注册之前，我们首先看一下NameServer到底存储哪些信息。

private final HashMap<String/* topic */, List<QueueData>> topicQueueTable;
private final HashMap<String/* brokerName */, BrokerData> brokerAddrTable;
private final HashMap<String/* clusterName */, Set<String/* brokerName */>> clusterAddrTable;
private final HashMap<String/* brokerAddr */, BrokerLiveInfo> brokerLiveTable;
private final HashMap<String/* brokerAddr */, List<String>/* Filter Server */> filterServerTable;

topicQueueTable:Topic消息队列路由信息，消息发送时根据路由表进行负载均衡。

brokerAddrTable:Broker基础信息，包含brokerName、所属集群名称、主备Broker地址。

brokerLiveTable:Broker状态信息。NameServer每次收到心跳包时会替换该信息。

filterServerTable:Broker上的FilterServer列表，用于类模式消息过滤，

public class QueueData implements Comparable<QueueData> {
    private String brokerName;
    private int readQueueNums;
    private int writeQueueNums;
    private int perm;
    private int topicSynFlag;
}

public class BrokerData implements Comparable<BrokerData> {
    private String cluster;
    private String brokerName;
    private HashMap<Long/* brokerId */, String/* broker address */> brokerAddrs;
}

class BrokerLiveInfo {
    // 上次收到Broker心跳包的时间
    private long lastUpdateTimestamp; 
    private DataVersion dataVersion;
    private Channel channel;
    private String haServerAddr;
}

多个Broker组成一个集群，BrokerName由相同的多台Broker组成Master-Slave架构，brokerId为0代表Master，大于0表示Slave。

路由注册

RocketMQ路由注册是通过Broker与NameServer的心跳功能实现的。Broker启动时向集群中所有的NameServer发送心跳语句，每隔30s向集群中所有NameServer发送心跳包，NameServer收到Broker心跳包时会更新brokerLiveTable缓存中BrokerLiveInfo的lastUpdate Timestamp，然后NameServer每隔10s扫描brokerLiveTable，如果连续120s没有收到心跳包，NameServer将移除该Broker的路由信息同时关闭Socket连接。

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