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Add documentation to concurrent multipart upload utility methods (#128821)
In the hope to make more sense of how the flux of byte buffer works. Also remove the synchronization on the input stream. Relates ES-11815
This commit is contained in:
Tanguy Leroux
GitHub
parent
28959c2e49
commit
f190a69f5f
1 changed files with 88 additions and 63 deletions
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@ -66,6 +66,7 @@ import org.elasticsearch.common.bytes.BytesReference;
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import org.elasticsearch.common.unit.ByteSizeUnit;
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import org.elasticsearch.common.unit.ByteSizeValue;
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import org.elasticsearch.common.util.BigArrays;
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import org.elasticsearch.core.Assertions;
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import org.elasticsearch.core.CheckedConsumer;
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import org.elasticsearch.core.IOUtils;
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import org.elasticsearch.core.Nullable;
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@ -74,6 +75,7 @@ import org.elasticsearch.repositories.RepositoriesMetrics;
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import org.elasticsearch.repositories.azure.AzureRepository.Repository;
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import org.elasticsearch.repositories.blobstore.ChunkedBlobOutputStream;
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import org.elasticsearch.rest.RestStatus;
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import org.elasticsearch.threadpool.ThreadPool;
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import java.io.FilterInputStream;
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import java.io.IOException;
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@ -101,6 +103,7 @@ import java.util.concurrent.ConcurrentHashMap;
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import java.util.concurrent.TimeUnit;
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import java.util.concurrent.atomic.AtomicInteger;
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import java.util.concurrent.atomic.AtomicLong;
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import java.util.concurrent.atomic.AtomicReference;
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import java.util.concurrent.atomic.LongAdder;
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import java.util.function.BiPredicate;
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import java.util.stream.Collectors;
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@ -507,7 +510,11 @@ public class AzureBlobStore implements BlobStore {
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return asyncClient.commitBlockList(
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multiParts.stream().map(MultiPart::blockId).toList(),
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failIfAlreadyExists == false
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).doOnSuccess(unused -> logger.debug("{}: all {} parts committed", blobName, multiParts.size()));
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)
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.doOnSuccess(unused -> logger.debug("{}: all {} parts committed", blobName, multiParts.size()))
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// Note: non-committed uploaded blocks will be deleted by Azure after a week
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// (see https://docs.microsoft.com/en-us/rest/api/storageservices/put-block#remarks)
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.doOnError(e -> logger.error(() -> format("%s: failed to commit %d parts", blobName, multiParts.size()), e));
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})
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.block();
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}
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@ -562,12 +569,13 @@ public class AzureBlobStore implements BlobStore {
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multiPart.blockOffset()
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);
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try {
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var stream = toSynchronizedInputStream(blobName, provider.apply(multiPart.blockOffset(), multiPart.blockSize()), multiPart);
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final var stream = provider.apply(multiPart.blockOffset(), multiPart.blockSize());
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assert stream.markSupported() : "provided input stream must support mark and reset";
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boolean success = false;
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try {
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var stageBlock = asyncClient.stageBlock(
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multiPart.blockId(),
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toFlux(stream, multiPart.blockSize(), DEFAULT_UPLOAD_BUFFERS_SIZE),
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toFlux(wrapInputStream(blobName, stream, multiPart), multiPart.blockSize(), DEFAULT_UPLOAD_BUFFERS_SIZE),
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multiPart.blockSize()
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).doOnSuccess(unused -> {
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logger.debug(() -> format("%s: part [%s] of size [%s] uploaded", blobName, multiPart.part(), multiPart.blockSize()));
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@ -760,88 +768,106 @@ public class AzureBlobStore implements BlobStore {
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// we read the input stream (i.e. when it's rate limited)
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}
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private static InputStream toSynchronizedInputStream(String blobName, InputStream delegate, MultiPart multipart) {
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assert delegate.markSupported() : "An InputStream with mark support was expected";
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// We need to introduce a read barrier in order to provide visibility for the underlying
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// input stream state as the input stream can be read from different threads.
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// TODO See if this is still needed
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/**
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* Wraps an {@link InputStream} to assert that it is read only by a single thread at a time and to add log traces.
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*/
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private static InputStream wrapInputStream(final String blobName, final InputStream delegate, final MultiPart multipart) {
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return new FilterInputStream(delegate) {
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private final AtomicReference<Thread> currentThread = Assertions.ENABLED ? new AtomicReference<>() : null;
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private final boolean isTraceEnabled = logger.isTraceEnabled();
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@Override
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public synchronized int read(byte[] b, int off, int len) throws IOException {
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public int read(byte[] b, int off, int len) throws IOException {
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assert assertThread(null, Thread.currentThread());
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assert ThreadPool.assertCurrentThreadPool(AzureRepositoryPlugin.REPOSITORY_THREAD_POOL_NAME);
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try {
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var result = super.read(b, off, len);
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if (isTraceEnabled) {
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logger.trace("{} reads {} bytes from {} part {}", Thread.currentThread(), result, blobName, multipart.part());
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}
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return result;
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} finally {
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assert assertThread(Thread.currentThread(), null);
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}
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}
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@Override
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public synchronized int read() throws IOException {
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public int read() throws IOException {
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assert assertThread(null, Thread.currentThread());
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assert ThreadPool.assertCurrentThreadPool(AzureRepositoryPlugin.REPOSITORY_THREAD_POOL_NAME);
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try {
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var result = super.read();
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if (isTraceEnabled) {
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logger.trace("{} reads {} byte from {} part {}", Thread.currentThread(), result, blobName, multipart.part());
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}
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return result;
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} finally {
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assert assertThread(Thread.currentThread(), null);
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}
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}
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@Override
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public synchronized void mark(int readlimit) {
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if (isTraceEnabled) {
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logger.trace("{} marks stream {} part {}", Thread.currentThread(), blobName, multipart.part());
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}
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super.mark(readlimit);
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}
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@Override
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public synchronized void reset() throws IOException {
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if (isTraceEnabled) {
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logger.trace("{} resets stream {} part {}", Thread.currentThread(), blobName, multipart.part());
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}
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super.reset();
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}
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@Override
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public synchronized void close() throws IOException {
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if (isTraceEnabled) {
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logger.trace("{} closes stream {} part {}", Thread.currentThread(), blobName, multipart.part());
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}
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super.close();
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}
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@Override
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public String toString() {
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return blobName + " part [" + multipart.part() + "] of size [" + multipart.blockSize() + ']';
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private boolean assertThread(Thread current, Thread updated) {
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final Thread witness = currentThread.compareAndExchange(current, updated);
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assert witness == current
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: "Unable to set current thread to ["
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+ updated
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+ "]: expected thread ["
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+ current
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+ "] to be the thread currently accessing the input stream for reading, but thread "
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+ witness
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+ " is already reading "
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+ blobName
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+ " part "
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+ multipart.part();
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return true;
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}
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};
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}
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private static Flux<ByteBuffer> toFlux(InputStream stream, long length, int chunkSize) {
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assert stream.markSupported() : "An InputStream with mark support was expected";
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// We need to mark the InputStream as it's possible that we need to retry for the same chunk
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/**
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* Converts an input stream to a Flux of ByteBuffer. This method also checks that the stream has provided the expected number of bytes.
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*
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* @param stream the input stream that needs to be converted
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* @param length the expected length in bytes of the input stream
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* @param byteBufferSize the size of the ByteBuffers to be created
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**/
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private static Flux<ByteBuffer> toFlux(InputStream stream, long length, final int byteBufferSize) {
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assert stream.markSupported() : "input stream must support mark and reset";
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// always marks the input stream in case it needs to be retried
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stream.mark(Integer.MAX_VALUE);
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// defer the creation of the flux until it is subscribed
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return Flux.defer(() -> {
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// TODO Code in this Flux.defer() can be concurrently executed by multiple threads?
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try {
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stream.reset();
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} catch (IOException e) {
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throw new RuntimeException(e);
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// Flux.defer() catches and propagates the exception
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throw new UncheckedIOException(e);
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}
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// the number of bytes read is updated in a thread pool (repository_azure) and later compared to the expected length in another
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// thread pool (azure_event_loop), so we need this to be atomic.
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final var bytesRead = new AtomicLong(0L);
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// This flux is subscribed by a downstream operator that finally queues the
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// buffers into netty output queue. Sadly we are not able to get a signal once
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// the buffer has been flushed, so we have to allocate those and let the GC to
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// reclaim them (see MonoSendMany). Additionally, that very same operator requests
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// 128 elements (that's hardcoded) once it's subscribed (later on, it requests
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// by 64 elements), that's why we provide 64kb buffers.
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// length is at most 100MB so it's safe to cast back to an integer in this case
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final int parts = (int) length / chunkSize;
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final long remaining = length % chunkSize;
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return Flux.range(0, remaining == 0 ? parts : parts + 1).map(i -> i * chunkSize).concatMap(pos -> Mono.fromCallable(() -> {
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long count = pos + chunkSize > length ? length - pos : chunkSize;
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assert length <= ByteSizeValue.ofMb(100L).getBytes() : length;
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// length is at most 100MB so it's safe to cast back to an integer
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final int parts = Math.toIntExact(length / byteBufferSize);
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final long remaining = length % byteBufferSize;
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// This flux is subscribed by a downstream subscriber (reactor.netty.channel.MonoSendMany) that queues the buffers into netty
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// output queue. Sadly we are not able to get a signal once the buffer has been flushed, so we have to allocate those and let
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// the GC to reclaim them. Additionally, the MonoSendMany subscriber requests 128 elements from the flux when it subscribes to
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// it. This 128 value is hardcoded in reactor.netty.channel.MonoSend.MAX_SIZE). After 128 byte buffers have been published by
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// the flux, the MonoSendMany subscriber requests 64 more byte buffers (see reactor.netty.channel.MonoSend.REFILL_SIZE) and so
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// on.
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//
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// So this flux instantiates 128 ByteBuffer objects of DEFAULT_UPLOAD_BUFFERS_SIZE bytes in heap every time the NettyOutbound in
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// the Azure's Netty event loop requests byte buffers to write to the network channel. That represents 128 * 64kb = 8 mb per
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// flux which is aligned with BlobAsyncClient.BLOB_DEFAULT_HTBB_UPLOAD_BLOCK_SIZE. The creation of the ByteBuffer objects are
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// forked to the repository_azure thread pool, which has a maximum of 15 threads (most of the time, can be less than that for
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// nodes with less than 750mb heap). It means that max. 15 * 8 = 120mb bytes are allocated on heap at a time here (omitting the
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// ones already created and pending garbage collection).
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return Flux.range(0, remaining == 0 ? parts : parts + 1).map(i -> i * byteBufferSize).concatMap(pos -> Mono.fromCallable(() -> {
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long count = pos + byteBufferSize > length ? length - pos : byteBufferSize;
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int numOfBytesRead = 0;
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int offset = 0;
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int len = (int) count;
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@ -867,9 +893,8 @@ public class AzureBlobStore implements BlobStore {
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);
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}
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});
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// We need to subscribe on a different scheduler to avoid blocking the io threads when we read the input stream
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// subscribe on a different scheduler to avoid blocking the network io threads when reading bytes from disk
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}).subscribeOn(Schedulers.elastic());
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}
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/**
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