RocketMQ-04、消息存储(6)
4.8.2.Broker异步刷盘
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();
}
}
}
// Asynchronous flush
else {
if (!this.defaultMessageStore.getMessageStoreConfig().isTransientStorePoolEnable()) {
flushCommitLogService.wakeup();
} else {
commitLogService.wakeup();
}
}
异步刷盘根据是否开启transientStorePoolEnable机制，刷盘实现会有细微差别。如果transientStorePoolEnable 为true , RocketMQ 会单独申请一个与目标物理文件（ commitlog)同样大小的堆外内存， 该堆外内存将使用内存锁定，确保不会被置换到虚拟内存中去，消息首先追加到堆外内存，然后提交到与物理文件的内存映射内存中，再flush 到磁盘。如果transientStorePoolEnable 为flalse ，消息直接追加到与物理文件直接映射的内存中，然后刷写到磁盘中。transientStorePoolEnable 为true 的磁盘刷写流程如图4-20 所示。
- 首先将消息直接追加到ByteBuffer （堆外内存DirectByteBuffer ), wrotePosition 随着消息的不断追加向后移动。
- CommitRealTimeService 线程默认每200ms 将ByteBuffer 新追加的内容（ wrotePosihon减去commitedPosition ）的数据提交到Ma ppedB yte Buff1巳r 中。
- MappedByt巳Buffer 在内存中追加提交的内容， wrotePosition 指针向前后移动， 然后返回。
- commit 操作成功返回，将commitedPosition 向前后移动本次提交的内容长度，此时wrotePosition 指针依然可以向前推进。
- FlushRealTimeService 线程默认每500ms 将MappedByteBuffer 中新追加的内存( wrotePosition 减去上一次刷写位置flushedPositiont ）通过调用MappedByteBuffer#force()方法将数据刷写到磁盘。
image
CommitRealTimeService 提交线程工作机制
@Override
public void run() {
CommitLog.log.info(this.getServiceName() + " service started");
while (!this.isStopped()) {
int interval = CommitLog.this.defaultMessageStore.getMessageStoreConfig().getCommitIntervalCommitLog();
int commitDataLeastPages = CommitLog.this.defaultMessageStore.getMessageStoreConfig().getCommitCommitLogLeastPages();
int commitDataThoroughInterval =
CommitLog.this.defaultMessageStore.getMessageStoreConfig().getCommitCommitLogThoroughInterval();
long begin = System.currentTimeMillis();
if (begin >= (this.lastCommitTimestamp + commitDataThoroughInterval)) {
this.lastCommitTimestamp = begin;
commitDataLeastPages = 0;
}
try {
boolean result = CommitLog.this.mappedFileQueue.commit(commitDataLeastPages);
long end = System.currentTimeMillis();
if (!result) {
this.lastCommitTimestamp = end; // result = false means some data committed.
//now wake up flush thread.
flushCommitLogService.wakeup();
}
if (end - begin > 500) {
log.info("Commit data to file costs {} ms", end - begin);
}
this.waitForRunning(interval);
} catch (Throwable e) {
CommitLog.log.error(this.getServiceName() + " service has exception. ", e);
}
}
boolean result = false;
for (int i = 0; i < RETRY_TIMES_OVER && !result; i++) {
result = CommitLog.this.mappedFileQueue.commit(0);
CommitLog.log.info(this.getServiceName() + " service shutdown, retry " + (i + 1) + " times " + (result ? "OK" : "Not OK"));