RocketMQ源码分析之消息异步刷盘

异步刷盘根据是否使用临时存储池分为先把直接内存中的数据提交到文件通道后刷盘和直接通过mmap刷盘

public boolean isTransientStorePoolEnable() {
    return transientStorePoolEnable && FlushDiskType.ASYNC_FLUSH == getFlushDiskType()
        && BrokerRole.SLAVE != getBrokerRole();
}

transientStorePoolEnable = false

刷盘线程为FlushRealTimeService，判断上一次刷盘的时间是否已经超过1000*10，超过的话就代表剩余消息全部刷盘即页数为0，默认每4页刷盘一次。

class FlushRealTimeService extends FlushCommitLogService {
    private long lastFlushTimestamp = 0;
    private long printTimes = 0;

    public void run() {
        CommitLog.log.info(this.getServiceName() + " service started");

        while (!this.isStopped()) {
            boolean flushCommitLogTimed = CommitLog.this.defaultMessageStore.getMessageStoreConfig().isFlushCommitLogTimed();

            int interval = CommitLog.this.defaultMessageStore.getMessageStoreConfig().getFlushIntervalCommitLog();
            int flushPhysicQueueLeastPages = CommitLog.this.defaultMessageStore.getMessageStoreConfig().getFlushCommitLogLeastPages();

            int flushPhysicQueueThoroughInterval =
                CommitLog.this.defaultMessageStore.getMessageStoreConfig().getFlushCommitLogThoroughInterval();

            boolean printFlushProgress = false;

            // Print flush progress
            long currentTimeMillis = System.currentTimeMillis();
            if (currentTimeMillis >= (this.lastFlushTimestamp + flushPhysicQueueThoroughInterval)) {
                this.lastFlushTimestamp = currentTimeMillis;
                flushPhysicQueueLeastPages = 0;
                printFlushProgress = (printTimes++ % 10) == 0;
            }

            try {
                if (flushCommitLogTimed) {
                    Thread.sleep(interval);
                } else {
                    this.waitForRunning(interval);
                }

                if (printFlushProgress) {
                    this.printFlushProgress();
                }

                long begin = System.currentTimeMillis();
                CommitLog.this.mappedFileQueue.flush(flushPhysicQueueLeastPages);
                long storeTimestamp = CommitLog.this.mappedFileQueue.getStoreTimestamp();
                if (storeTimestamp > 0) {
                    CommitLog.this.defaultMessageStore.getStoreCheckpoint().setPhysicMsgTimestamp(storeTimestamp);
                }
                long past = System.currentTimeMillis() - begin;
                if (past > 500) {
                    log.info("Flush data to disk costs {} ms", past);
                }
            } catch (Throwable e) {
                CommitLog.log.warn(this.getServiceName() + " service has exception. ", e);
                this.printFlushProgress();
            }
        }

        // Normal shutdown, to ensure that all the flush before exit
        boolean result = false;
        for (int i = 0; i < RETRY_TIMES_OVER && !result; i++) {
            result = CommitLog.this.mappedFileQueue.flush(0);
            CommitLog.log.info(this.getServiceName() + " service shutdown, retry " + (i + 1) + " times " + (result ? "OK" : "Not OK"));
        }

        this.printFlushProgress();

        CommitLog.log.info(this.getServiceName() + " service end");
    }

    @Override
    public String getServiceName() {
        return FlushRealTimeService.class.getSimpleName();
    }

    private void printFlushProgress() {
        // CommitLog.log.info("how much disk fall behind memory, "
        // + CommitLog.this.mappedFileQueue.howMuchFallBehind());
    }

    @Override
    public long getJointime() {
        return 1000 * 60 * 5;
    }
}

 

transientStorePoolEnable = true

刷盘线程为CommitRealTimeService，提交间隔时间为200ms，判断少次提交时间是否超过该时间，超过的话就全部提交到文件通道，否则就是每4页提交一次

class CommitRealTimeService extends FlushCommitLogService {

    private long lastCommitTimestamp = 0;

    @Override
    public String getServiceName() {
        return CommitRealTimeService.class.getSimpleName();
    }

    @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"));
        }
        CommitLog.log.info(this.getServiceName() + " service end");
    }
}

提交数据，查找需要进行提交的文件

public boolean commit(final int commitLeastPages) {
    boolean result = true;
    MappedFile mappedFile = this.findMappedFileByOffset(this.committedWhere, this.committedWhere == 0);
    if (mappedFile != null) {
        int offset = mappedFile.commit(commitLeastPages);
        long where = mappedFile.getFileFromOffset() + offset;
        result = where == this.committedWhere;
        this.committedWhere = where;
    }

    return result;
}

如果writeBuffer为空的话直接返回写下标就行，目前没有适用的地方，判断是否可以提交，磁盘是否已经写满，写下标与提交下标是否达到对应的页数，对进行文件引用即现在可否可持有文件

public int commit(final int commitLeastPages) {
    if (writeBuffer == null) {
        //no need to commit data to file channel, so just regard wrotePosition as committedPosition.
        return this.wrotePosition.get();
    }
    if (this.isAbleToCommit(commitLeastPages)) {
        if (this.hold()) {
            commit0(commitLeastPages);
            this.release();
        } else {
            log.warn("in commit, hold failed, commit offset = " + this.committedPosition.get());
        }
    }

    // All dirty data has been committed to FileChannel.
    if (writeBuffer != null && this.transientStorePool != null && this.fileSize == this.committedPosition.get()) {
        this.transientStorePool.returnBuffer(writeBuffer);
        this.writeBuffer = null;
    }

    return this.committedPosition.get();
}
protected boolean isAbleToCommit(final int commitLeastPages) {
    int flush = this.committedPosition.get();
    int write = this.wrotePosition.get();

    if (this.isFull()) {
        return true;
    }

    if (commitLeastPages > 0) {
        return ((write / OS_PAGE_SIZE) - (flush / OS_PAGE_SIZE)) >= commitLeastPages;
    }

    return write > flush;
}

 

进行数据提交，把直接内存中的数据写入文件通道中，设置提交下标，最后释放文件引用，判断目前的提交下标是否等于文件大小，最后回收直接内存重利用，释放该文件的直接内存的引用

protected void commit0(final int commitLeastPages) {
    int writePos = this.wrotePosition.get();
    int lastCommittedPosition = this.committedPosition.get();

    if (writePos - this.committedPosition.get() > 0) {
        try {
            ByteBuffer byteBuffer = writeBuffer.slice();
            byteBuffer.position(lastCommittedPosition);
            byteBuffer.limit(writePos);
            this.fileChannel.position(lastCommittedPosition);
            this.fileChannel.write(byteBuffer);
            this.committedPosition.set(writePos);
        } catch (Throwable e) {
            log.error("Error occurred when commit data to FileChannel.", e);
        }
    }
}
public void returnBuffer(ByteBuffer byteBuffer) {
    byteBuffer.position(0);
    byteBuffer.limit(fileSize);
    this.availableBuffers.offerFirst(byteBuffer);
}

返回提交下标，设置最新额提交下标committedWhere，如果数据提交会返回false，没有的话返回true。如果有数据提交的话会触发flushCommitLogService.wakeup()，然后执行刷盘操作，刷盘操作是通过this.fileChannel.force(false);来操作。