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);
}
}
}
}