RocketMQ 主从同步

RocketMQ 的主和从一直在使用 nio 进行数据同步:

master

master 监听端口

org.apache.rocketmq.store.ha.HAService.AcceptSocketService#beginAccept

master 建立连接

org.apache.rocketmq.store.ha.HAService.AcceptSocketService#run

master 读取 slave 上报的 maxOffset

org.apache.rocketmq.store.ha.HAConnection.ReadSocketService#run

master 传输数据给 slave

org.apache.rocketmq.store.ha.HAConnection.WriteSocketService#run

slave

slave 连接 master

org.apache.rocketmq.store.ha.HAService.HAClient#connectMaster

slave 定时报告 maxOffset 给 master

org.apache.rocketmq.store.ha.HAService.HAClient#run

slave 接收 master 传输来的数据

org.apache.rocketmq.store.ha.HAService.HAClient#processReadEvent

这里的同步，暂时只涉及到 commitLog。

同步双写的本质，master 先写磁盘，然后等待 slave 同步消息成功。

写磁盘：

public void handleDiskFlush(AppendMessageResult result, PutMessageResult putMessageResult, MessageExt messageExt) {

    // Synchronization flush

    if (FlushDiskType.SYNC_FLUSH == this.defaultMessageStore.getMessageStoreConfig().getFlushDiskType()) {

        final GroupCommitService service = (GroupCommitService) this.flushCommitLogService;

        if (messageExt.isWaitStoreMsgOK()) {

            GroupCommitRequest request = new GroupCommitRequest(result.getWroteOffset() + result.getWroteBytes());

            service.putRequest(request);

            boolean flushOK = request.waitForFlush(this.defaultMessageStore.getMessageStoreConfig().getSyncFlushTimeout());

            if (!flushOK) {

                log.error("do groupcommit, wait for flush failed, topic: " + messageExt.getTopic() + " tags: " + messageExt.getTags()

                    + " client address: " + messageExt.getBornHostString());

                putMessageResult.setPutMessageStatus(PutMessageStatus.FLUSH_DISK_TIMEOUT);

            }

        } else {

            service.wakeup();

        }

    }

    // Asynchronous flush

    else {

        if (!this.defaultMessageStore.getMessageStoreConfig().isTransientStorePoolEnable()) {

            flushCommitLogService.wakeup();

        } else {

            commitLogService.wakeup();

        }

    }

}

同步到 slave：

// org.apache.rocketmq.store.CommitLog#handleHA

public void handleHA(AppendMessageResult result, PutMessageResult putMessageResult, MessageExt messageExt) {

    // SYNC_MASTER 则执行逻辑

    if (BrokerRole.SYNC_MASTER == this.defaultMessageStore.getMessageStoreConfig().getBrokerRole()) {

        HAService service = this.defaultMessageStore.getHaService();

        if (messageExt.isWaitStoreMsgOK()) {

            // Determine whether to wait

            // slave 没有落后 master 太多

            if (service.isSlaveOK(result.getWroteOffset() + result.getWroteBytes())) {

                GroupCommitRequest request = new GroupCommitRequest(result.getWroteOffset() + result.getWroteBytes());

                // 创建 GroupCommitRequest 放入 GroupTransferService 的 requestsWrite 中

                // GroupTransferService.run 会一直比较 GroupCommitRequest#nextOffset 和 slave 已提交的位移

                service.putRequest(request);

                service.getWaitNotifyObject().wakeupAll();

                // 等待 5 秒，检查 slave 的同步结果

                boolean flushOK =

                    request.waitForFlush(this.defaultMessageStore.getMessageStoreConfig().getSyncFlushTimeout());

                if (!flushOK) {

                    log.error("do sync transfer other node, wait return, but failed, topic: " + messageExt.getTopic() + " tags: "

                        + messageExt.getTags() + " client address: " + messageExt.getBornHostNameString());

                    putMessageResult.setPutMessageStatus(PutMessageStatus.FLUSH_SLAVE_TIMEOUT);

                }

            }

            // Slave problem

            else {

                // Tell the producer, slave not available

                putMessageResult.setPutMessageStatus(PutMessageStatus.SLAVE_NOT_AVAILABLE);

            }

        }

    }

}