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https://issues.apache.org/jira/browse/HADOOP-19613?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=18008572#comment-18008572
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ASF GitHub Bot commented on HADOOP-19613:
-----------------------------------------
manika137 commented on code in PR #7801:
URL: https://github.com/apache/hadoop/pull/7801#discussion_r2218102748
##########
hadoop-tools/hadoop-azure/src/main/java/org/apache/hadoop/fs/azurebfs/services/ReadBufferManagerV1.java:
##########
@@ -0,0 +1,637 @@
+/**
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements. See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership. The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License. You may obtain a copy of the License at
+ * <p>
+ * http://www.apache.org/licenses/LICENSE-2.0
+ * <p>
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.hadoop.fs.azurebfs.services;
+
+import org.apache.hadoop.fs.azurebfs.contracts.services.ReadBufferStatus;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+import java.io.IOException;
+import java.util.ArrayList;
+import java.util.Collection;
+import java.util.Iterator;
+import java.util.LinkedList;
+import java.util.List;
+import java.util.Queue;
+import java.util.Stack;
+import java.util.concurrent.CountDownLatch;
+import java.util.concurrent.locks.ReentrantLock;
+
+import org.apache.hadoop.fs.azurebfs.utils.TracingContext;
+import org.apache.hadoop.classification.VisibleForTesting;
+
+/**
+ * The Read Buffer Manager for Rest AbfsClient.
+ * V1 implementation of ReadBufferManager.
+ */
+final class ReadBufferManagerV1 implements ReadBufferManager {
+ private static final Logger LOGGER = LoggerFactory.getLogger(
+ ReadBufferManagerV1.class);
+ private static final int ONE_KB = 1024;
+ private static final int ONE_MB = ONE_KB * ONE_KB;
+
+ private static final int NUM_BUFFERS = 16;
+ private static final int NUM_THREADS = 8;
+ private static final int DEFAULT_THRESHOLD_AGE_MILLISECONDS = 3000; // have
to see if 3 seconds is a good threshold
+
+ private static int blockSize = 4 * ONE_MB;
+ private static int thresholdAgeMilliseconds =
DEFAULT_THRESHOLD_AGE_MILLISECONDS;
+ private Thread[] threads = new Thread[NUM_THREADS];
+ private byte[][] buffers; // array of byte[] buffers, to hold the data
that is read
+ private Stack<Integer> freeList = new Stack<>(); // indices in buffers[]
array that are available
+
+ private Queue<ReadBuffer> readAheadQueue = new LinkedList<>(); // queue of
requests that are not picked up by any worker thread yet
+ private LinkedList<ReadBuffer> inProgressList = new LinkedList<>(); //
requests being processed by worker threads
+ private LinkedList<ReadBuffer> completedReadList = new LinkedList<>(); //
buffers available for reading
+ private static ReadBufferManagerV1 bufferManager; // singleton, initialized
in static initialization block
+ private static final ReentrantLock LOCK = new ReentrantLock();
+
+ static ReadBufferManagerV1 getBufferManager() {
+ if (bufferManager == null) {
+ LOCK.lock();
+ try {
+ if (bufferManager == null) {
+ bufferManager = new ReadBufferManagerV1();
+ bufferManager.init();
+ }
+ } finally {
+ LOCK.unlock();
+ }
+ }
+ return bufferManager;
+ }
+
+ static void setReadBufferManagerConfigs(int readAheadBlockSize) {
+ if (bufferManager == null) {
+ LOGGER.debug(
+ "ReadBufferManagerV1 not initialized yet. Overriding
readAheadBlockSize as {}",
+ readAheadBlockSize);
+ blockSize = readAheadBlockSize;
+ }
+ }
+
+ private void init() {
+ buffers = new byte[NUM_BUFFERS][];
+ for (int i = 0; i < NUM_BUFFERS; i++) {
+ buffers[i] = new byte[blockSize]; // same buffers are reused. The byte
array never goes back to GC
+ freeList.add(i);
+ }
+ for (int i = 0; i < NUM_THREADS; i++) {
+ Thread t = new Thread(new ReadBufferWorker(i));
+ t.setDaemon(true);
+ threads[i] = t;
+ t.setName("ABFS-prefetch-" + i);
+ t.start();
+ }
+ ReadBufferWorker.UNLEASH_WORKERS.countDown();
+ }
+
+ // hide instance constructor
+ private ReadBufferManagerV1() {
+ LOGGER.trace("Creating readbuffer manager with HADOOP-18546 patch");
+ }
+
+ /**
+ * {@link AbfsInputStream} calls this method to queue read-aheads.
+ *
+ * @param stream The {@link AbfsInputStream} for which to do the
read-ahead
+ * @param requestedOffset The offset in the file which shoukd be read
+ * @param requestedLength The length to read
+ */
+ @Override
+ public void queueReadAhead(final AbfsInputStream stream, final long
requestedOffset, final int requestedLength,
+ TracingContext tracingContext) {
+ if (LOGGER.isTraceEnabled()) {
+ LOGGER.trace("Start Queueing readAhead for {} offset {} length {}",
+ stream.getPath(), requestedOffset, requestedLength);
+ }
+ ReadBuffer buffer;
+ synchronized (this) {
+ if (isAlreadyQueued(stream, requestedOffset)) {
+ return; // already queued, do not queue again
+ }
+ if (freeList.isEmpty() && !tryEvict()) {
+ return; // no buffers available, cannot queue anything
+ }
+
+ buffer = new ReadBuffer();
+ buffer.setStream(stream);
+ buffer.setOffset(requestedOffset);
+ buffer.setLength(0);
+ buffer.setRequestedLength(requestedLength);
+ buffer.setStatus(ReadBufferStatus.NOT_AVAILABLE);
+ buffer.setLatch(new CountDownLatch(1));
+ buffer.setTracingContext(tracingContext);
+
+ Integer bufferIndex = freeList.pop(); // will return a value, since we
have checked size > 0 already
+
+ buffer.setBuffer(buffers[bufferIndex]);
+ buffer.setBufferindex(bufferIndex);
+ readAheadQueue.add(buffer);
+ notifyAll();
+ if (LOGGER.isTraceEnabled()) {
+ LOGGER.trace("Done q-ing readAhead for file {} offset {} buffer idx
{}",
+ stream.getPath(), requestedOffset, buffer.getBufferindex());
+ }
+ }
+ }
+
+ /**
+ * {@link AbfsInputStream} calls this method read any bytes already
available in a buffer (thereby saving a
+ * remote read). This returns the bytes if the data already exists in
buffer. If there is a buffer that is reading
+ * the requested offset, then this method blocks until that read completes.
If the data is queued in a read-ahead
+ * but not picked up by a worker thread yet, then it cancels that read-ahead
and reports cache miss. This is because
+ * depending on worker thread availability, the read-ahead may take a while
- the calling thread can do it's own
+ * read to get the data faster (copmared to the read waiting in queue for an
indeterminate amount of time).
+ *
+ * @param stream the file to read bytes for
+ * @param position the offset in the file to do a read for
+ * @param length the length to read
+ * @param buffer the buffer to read data into. Note that the buffer will
be written into from offset 0.
+ * @return the number of bytes read
+ */
+ @Override
+ public int getBlock(final AbfsInputStream stream, final long position, final
int length, final byte[] buffer)
+ throws IOException {
+ // not synchronized, so have to be careful with locking
+ if (LOGGER.isTraceEnabled()) {
+ LOGGER.trace("getBlock for file {} position {} thread {}",
+ stream.getPath(), position, Thread.currentThread().getName());
+ }
+
+ waitForProcess(stream, position);
+
+ int bytesRead = 0;
+ synchronized (this) {
+ bytesRead = getBlockFromCompletedQueue(stream, position, length, buffer);
+ }
+ if (bytesRead > 0) {
+ if (LOGGER.isTraceEnabled()) {
+ LOGGER.trace("Done read from Cache for {} position {} length {}",
+ stream.getPath(), position, bytesRead);
+ }
+ return bytesRead;
+ }
+
+ // otherwise, just say we got nothing - calling thread can do its own read
+ return 0;
+ }
+
+ /**
+ * ReadBufferWorker thread calls this to get the next buffer that it should
work on.
+ *
+ * @return {@link ReadBuffer}
+ * @throws InterruptedException if thread is interrupted
+ */
+ @Override
+ public ReadBuffer getNextBlockToRead() throws InterruptedException {
+ ReadBuffer buffer = null;
+ synchronized (this) {
+ //buffer = readAheadQueue.take(); // blocking method
+ while (readAheadQueue.size() == 0) {
+ wait();
+ }
+ buffer = readAheadQueue.remove();
+ notifyAll();
+ if (buffer == null) {
+ return null; // should never happen
+ }
+ buffer.setStatus(ReadBufferStatus.READING_IN_PROGRESS);
+ inProgressList.add(buffer);
+ }
+ if (LOGGER.isTraceEnabled()) {
+ LOGGER.trace("ReadBufferWorker picked file {} for offset {}",
+ buffer.getStream().getPath(), buffer.getOffset());
+ }
+ return buffer;
+ }
+
+ /**
+ * ReadBufferWorker thread calls this method to post completion.
+ *
+ * @param buffer the buffer whose read was completed
+ * @param result the {@link ReadBufferStatus} after the read
operation in the worker thread
+ * @param bytesActuallyRead the number of bytes that the worker thread was
actually able to read
+ */
+ @Override
+ public void doneReading(final ReadBuffer buffer, final ReadBufferStatus
result, final int bytesActuallyRead) {
+ if (LOGGER.isTraceEnabled()) {
+ LOGGER.trace("ReadBufferWorker completed read file {} for offset {}
outcome {} bytes {}",
+ buffer.getStream().getPath(), buffer.getOffset(), result,
bytesActuallyRead);
+ }
+ synchronized (this) {
+ // If this buffer has already been purged during
+ // close of InputStream then we don't update the lists.
+ if (inProgressList.contains(buffer)) {
+ inProgressList.remove(buffer);
+ if (result == ReadBufferStatus.AVAILABLE && bytesActuallyRead > 0) {
+ buffer.setStatus(ReadBufferStatus.AVAILABLE);
+ buffer.setLength(bytesActuallyRead);
+ } else {
+ freeList.push(buffer.getBufferindex());
+ // buffer will be deleted as per the eviction policy.
+ }
+ // completed list also contains FAILED read buffers
+ // for sending exception message to clients.
+ buffer.setStatus(result);
+ buffer.setTimeStamp(currentTimeMillis());
+ completedReadList.add(buffer);
+ }
+ }
+
+ //outside the synchronized, since anyone receiving a wake-up from the
latch must see safe-published results
+ buffer.getLatch().countDown(); // wake up waiting threads (if any)
+ }
+
+ /**
+ * Purging the buffers associated with an {@link AbfsInputStream}
+ * from {@link ReadBufferManagerV1} when stream is closed.
+ * @param stream input stream.
+ */
+ @Override
+ public synchronized void purgeBuffersForStream(AbfsInputStream stream) {
+ LOGGER.debug("Purging stale buffers for AbfsInputStream {} ", stream);
+ readAheadQueue.removeIf(readBuffer -> readBuffer.getStream() == stream);
+ purgeList(stream, completedReadList);
+ }
+
+ private void waitForProcess(final AbfsInputStream stream, final long
position) {
+ ReadBuffer readBuf;
+ synchronized (this) {
+ clearFromReadAheadQueue(stream, position);
+ readBuf = getFromList(inProgressList, stream, position);
+ }
+ if (readBuf != null) { // if in in-progress queue, then block for
it
+ try {
+ if (LOGGER.isTraceEnabled()) {
+ LOGGER.trace("got a relevant read buffer for file {} offset {}
buffer idx {}",
+ stream.getPath(), readBuf.getOffset(), readBuf.getBufferindex());
+ }
+ readBuf.getLatch().await(); // blocking wait on the caller stream's
thread
+ // Note on correctness: readBuf gets out of inProgressList only in 1
place: after worker thread
+ // is done processing it (in doneReading). There, the latch is set
after removing the buffer from
+ // inProgressList. So this latch is safe to be outside the
synchronized block.
+ // Putting it in synchronized would result in a deadlock, since this
thread would be holding the lock
+ // while waiting, so no one will be able to change any state. If this
becomes more complex in the future,
+ // then the latch cane be removed and replaced with wait/notify
whenever inProgressList is touched.
+ } catch (InterruptedException ex) {
+ Thread.currentThread().interrupt();
+ }
+ if (LOGGER.isTraceEnabled()) {
+ LOGGER.trace("latch done for file {} buffer idx {} length {}",
+ stream.getPath(), readBuf.getBufferindex(), readBuf.getLength());
+ }
+ }
+ }
+
+ /**
+ * If any buffer in the completedlist can be reclaimed then reclaim it and
return the buffer to free list.
+ * The objective is to find just one buffer - there is no advantage to
evicting more than one.
+ *
+ * @return whether the eviction succeeeded - i.e., were we able to free up
one buffer
+ */
+ private synchronized boolean tryEvict() {
+ ReadBuffer nodeToEvict = null;
+ if (completedReadList.size() <= 0) {
+ return false; // there are no evict-able buffers
+ }
+
+ long currentTimeInMs = currentTimeMillis();
+
+ // first, try buffers where all bytes have been consumed (approximated as
first and last bytes consumed)
+ for (ReadBuffer buf : completedReadList) {
+ if (buf.isFirstByteConsumed() && buf.isLastByteConsumed()) {
+ nodeToEvict = buf;
+ break;
+ }
+ }
+ if (nodeToEvict != null) {
+ return evict(nodeToEvict);
+ }
+
+ // next, try buffers where any bytes have been consumed (may be a bad
idea? have to experiment and see)
+ for (ReadBuffer buf : completedReadList) {
+ if (buf.isAnyByteConsumed()) {
+ nodeToEvict = buf;
+ break;
+ }
+ }
+
+ if (nodeToEvict != null) {
+ return evict(nodeToEvict);
+ }
+
+ // next, try any old nodes that have not been consumed
+ // Failed read buffers (with buffer index=-1) that are older than
+ // thresholdAge should be cleaned up, but at the same time should not
+ // report successful eviction.
+ // Queue logic expects that a buffer is freed up for read ahead when
+ // eviction is successful, whereas a failed ReadBuffer would have released
+ // its buffer when its status was set to READ_FAILED.
+ long earliestBirthday = Long.MAX_VALUE;
+ ArrayList<ReadBuffer> oldFailedBuffers = new ArrayList<>();
+ for (ReadBuffer buf : completedReadList) {
+ if ((buf.getBufferindex() != -1)
+ && (buf.getTimeStamp() < earliestBirthday)) {
+ nodeToEvict = buf;
+ earliestBirthday = buf.getTimeStamp();
+ } else if ((buf.getBufferindex() == -1)
+ && (currentTimeInMs - buf.getTimeStamp()) >
thresholdAgeMilliseconds) {
+ oldFailedBuffers.add(buf);
+ }
+ }
+
+ for (ReadBuffer buf : oldFailedBuffers) {
+ evict(buf);
+ }
+
+ if ((currentTimeInMs - earliestBirthday > thresholdAgeMilliseconds) &&
(nodeToEvict != null)) {
+ return evict(nodeToEvict);
+ }
+
+ LOGGER.trace("No buffer eligible for eviction");
+ // nothing can be evicted
+ return false;
+ }
+
+ private boolean evict(final ReadBuffer buf) {
+ // As failed ReadBuffers (bufferIndx = -1) are saved in completedReadList,
+ // avoid adding it to freeList.
+ if (buf.getBufferindex() != -1) {
+ freeList.push(buf.getBufferindex());
+ }
+
+ completedReadList.remove(buf);
+ buf.setTracingContext(null);
+ if (LOGGER.isTraceEnabled()) {
+ LOGGER.trace("Evicting buffer idx {}; was used for file {} offset {}
length {}",
+ buf.getBufferindex(), buf.getStream().getPath(), buf.getOffset(),
buf.getLength());
+ }
+ return true;
+ }
+
+ private boolean isAlreadyQueued(final AbfsInputStream stream, final long
requestedOffset) {
+ // returns true if any part of the buffer is already queued
+ return (isInList(readAheadQueue, stream, requestedOffset)
+ || isInList(inProgressList, stream, requestedOffset)
+ || isInList(completedReadList, stream, requestedOffset));
+ }
+
+ private boolean isInList(final Collection<ReadBuffer> list, final
AbfsInputStream stream, final long requestedOffset) {
+ return (getFromList(list, stream, requestedOffset) != null);
+ }
+
+ private ReadBuffer getFromList(final Collection<ReadBuffer> list, final
AbfsInputStream stream, final long requestedOffset) {
+ for (ReadBuffer buffer : list) {
+ if (buffer.getStream() == stream) {
+ if (buffer.getStatus() == ReadBufferStatus.AVAILABLE
+ && requestedOffset >= buffer.getOffset()
+ && requestedOffset < buffer.getOffset() + buffer.getLength()) {
+ return buffer;
+ } else if (requestedOffset >= buffer.getOffset()
+ && requestedOffset < buffer.getOffset() +
buffer.getRequestedLength()) {
+ return buffer;
+ }
+ }
+ }
+ return null;
+ }
+
+ /**
+ * Returns buffers that failed or passed from completed queue.
+ * @param stream
+ * @param requestedOffset
+ * @return
Review Comment:
nit: missing @return ReadBuffer
> ABFS: [ReadAheadV2] Refactor ReadBufferManager to isolate new code with the
> current working code
> ------------------------------------------------------------------------------------------------
>
> Key: HADOOP-19613
> URL: https://issues.apache.org/jira/browse/HADOOP-19613
> Project: Hadoop Common
> Issue Type: Sub-task
> Components: fs/azure
> Affects Versions: 3.5.0, 3.4.1
> Reporter: Anuj Modi
> Assignee: Anuj Modi
> Priority: Major
> Labels: pull-request-available
>
> Read Buffer Manager used today was introduced way back and has been stable
> for quite a while.
> Read Buffer Manager to be introduced as part of
> https://issues.apache.org/jira/browse/HADOOP-19596 will introduce many
> changes incrementally over time. While the development goes on and we are
> able to fully stabilise the optimized version we need the current flow to be
> functional and undisturbed.
> This work item is to isolate that from new code by refactoring
> ReadBufferManager class to have 2 different implementations with same public
> interfaces: ReadBufferManagerV1 and ReadBufferManagerV2.
> This will also introduce new configs that can be used to toggle between new
> and old code.
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