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Posted to commits@spark.apache.org by we...@apache.org on 2018/02/15 09:09:11 UTC
spark git commit: [SPARK-23366] Improve hot reading path in
ReadAheadInputStream
Repository: spark
Updated Branches:
refs/heads/master f38c76063 -> 7539ae59d
[SPARK-23366] Improve hot reading path in ReadAheadInputStream
## What changes were proposed in this pull request?
`ReadAheadInputStream` was introduced in https://github.com/apache/spark/pull/18317/ to optimize reading spill files from disk.
However, from the profiles it seems that the hot path of reading small amounts of data (like readInt) is inefficient - it involves taking locks, and multiple checks.
Optimize locking: Lock is not needed when simply accessing the active buffer. Only lock when needing to swap buffers or trigger async reading, or get information about the async state.
Optimize short-path single byte reads, that are used e.g. by Java library DataInputStream.readInt.
The asyncReader used to call "read" only once on the underlying stream, that never filled the underlying buffer when it was wrapping an LZ4BlockInputStream. If the buffer was returned unfilled, that would trigger the async reader to be triggered to fill the read ahead buffer on each call, because the reader would see that the active buffer is below the refill threshold all the time.
However, filling the full buffer all the time could introduce increased latency, so also add an `AtomicBoolean` flag for the async reader to return earlier if there is a reader waiting for data.
Remove `readAheadThresholdInBytes` and instead immediately trigger async read when switching the buffers. It allows to simplify code paths, especially the hot one that then only has to check if there is available data in the active buffer, without worrying if it needs to retrigger async read. It seems to have positive effect on perf.
## How was this patch tested?
It was noticed as a regression in some workloads after upgrading to Spark 2.3.
It was particularly visible on TPCDS Q95 running on instances with fast disk (i3 AWS instances).
Running with profiling:
* Spark 2.2 - 5.2-5.3 minutes 9.5% in LZ4BlockInputStream.read
* Spark 2.3 - 6.4-6.6 minutes 31.1% in ReadAheadInputStream.read
* Spark 2.3 + fix - 5.3-5.4 minutes 13.3% in ReadAheadInputStream.read - very slightly slower, practically within noise.
We didn't see other regressions, and many workloads in general seem to be faster with Spark 2.3 (not investigated if thanks to async readed, or unrelated).
Author: Juliusz Sompolski <ju...@databricks.com>
Closes #20555 from juliuszsompolski/SPARK-23366.
Project: http://git-wip-us.apache.org/repos/asf/spark/repo
Commit: http://git-wip-us.apache.org/repos/asf/spark/commit/7539ae59
Tree: http://git-wip-us.apache.org/repos/asf/spark/tree/7539ae59
Diff: http://git-wip-us.apache.org/repos/asf/spark/diff/7539ae59
Branch: refs/heads/master
Commit: 7539ae59d6c354c95c50528abe9ddff6972e960f
Parents: f38c760
Author: Juliusz Sompolski <ju...@databricks.com>
Authored: Thu Feb 15 17:09:06 2018 +0800
Committer: Wenchen Fan <we...@databricks.com>
Committed: Thu Feb 15 17:09:06 2018 +0800
----------------------------------------------------------------------
.../apache/spark/io/ReadAheadInputStream.java | 119 +++++++++----------
.../unsafe/sort/UnsafeSorterSpillReader.java | 10 +-
.../spark/io/GenericFileInputStreamSuite.java | 98 ++++++++-------
.../spark/io/NioBufferedInputStreamSuite.java | 6 +-
.../spark/io/ReadAheadInputStreamSuite.java | 17 ++-
5 files changed, 133 insertions(+), 117 deletions(-)
----------------------------------------------------------------------
http://git-wip-us.apache.org/repos/asf/spark/blob/7539ae59/core/src/main/java/org/apache/spark/io/ReadAheadInputStream.java
----------------------------------------------------------------------
diff --git a/core/src/main/java/org/apache/spark/io/ReadAheadInputStream.java b/core/src/main/java/org/apache/spark/io/ReadAheadInputStream.java
index 5b45d26..0cced9e 100644
--- a/core/src/main/java/org/apache/spark/io/ReadAheadInputStream.java
+++ b/core/src/main/java/org/apache/spark/io/ReadAheadInputStream.java
@@ -27,6 +27,7 @@ import java.io.InterruptedIOException;
import java.nio.ByteBuffer;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.TimeUnit;
+import java.util.concurrent.atomic.AtomicBoolean;
import java.util.concurrent.locks.Condition;
import java.util.concurrent.locks.ReentrantLock;
@@ -78,9 +79,8 @@ public class ReadAheadInputStream extends InputStream {
// whether there is a read ahead task running,
private boolean isReading;
- // If the remaining data size in the current buffer is below this threshold,
- // we issue an async read from the underlying input stream.
- private final int readAheadThresholdInBytes;
+ // whether there is a reader waiting for data.
+ private AtomicBoolean isWaiting = new AtomicBoolean(false);
private final InputStream underlyingInputStream;
@@ -97,20 +97,13 @@ public class ReadAheadInputStream extends InputStream {
*
* @param inputStream The underlying input stream.
* @param bufferSizeInBytes The buffer size.
- * @param readAheadThresholdInBytes If the active buffer has less data than the read-ahead
- * threshold, an async read is triggered.
*/
public ReadAheadInputStream(
- InputStream inputStream, int bufferSizeInBytes, int readAheadThresholdInBytes) {
+ InputStream inputStream, int bufferSizeInBytes) {
Preconditions.checkArgument(bufferSizeInBytes > 0,
"bufferSizeInBytes should be greater than 0, but the value is " + bufferSizeInBytes);
- Preconditions.checkArgument(readAheadThresholdInBytes > 0 &&
- readAheadThresholdInBytes < bufferSizeInBytes,
- "readAheadThresholdInBytes should be greater than 0 and less than bufferSizeInBytes, " +
- "but the value is " + readAheadThresholdInBytes);
activeBuffer = ByteBuffer.allocate(bufferSizeInBytes);
readAheadBuffer = ByteBuffer.allocate(bufferSizeInBytes);
- this.readAheadThresholdInBytes = readAheadThresholdInBytes;
this.underlyingInputStream = inputStream;
activeBuffer.flip();
readAheadBuffer.flip();
@@ -166,12 +159,17 @@ public class ReadAheadInputStream extends InputStream {
// in that case the reader waits for this async read to complete.
// So there is no race condition in both the situations.
int read = 0;
+ int off = 0, len = arr.length;
Throwable exception = null;
try {
- while (true) {
- read = underlyingInputStream.read(arr);
- if (0 != read) break;
- }
+ // try to fill the read ahead buffer.
+ // if a reader is waiting, possibly return early.
+ do {
+ read = underlyingInputStream.read(arr, off, len);
+ if (read <= 0) break;
+ off += read;
+ len -= read;
+ } while (len > 0 && !isWaiting.get());
} catch (Throwable ex) {
exception = ex;
if (ex instanceof Error) {
@@ -181,13 +179,12 @@ public class ReadAheadInputStream extends InputStream {
}
} finally {
stateChangeLock.lock();
+ readAheadBuffer.limit(off);
if (read < 0 || (exception instanceof EOFException)) {
endOfStream = true;
} else if (exception != null) {
readAborted = true;
readException = exception;
- } else {
- readAheadBuffer.limit(read);
}
readInProgress = false;
signalAsyncReadComplete();
@@ -230,7 +227,10 @@ public class ReadAheadInputStream extends InputStream {
private void waitForAsyncReadComplete() throws IOException {
stateChangeLock.lock();
+ isWaiting.set(true);
try {
+ // There is only one reader, and one writer, so the writer should signal only once,
+ // but a while loop checking the wake up condition is still needed to avoid spurious wakeups.
while (readInProgress) {
asyncReadComplete.await();
}
@@ -239,6 +239,7 @@ public class ReadAheadInputStream extends InputStream {
iio.initCause(e);
throw iio;
} finally {
+ isWaiting.set(false);
stateChangeLock.unlock();
}
checkReadException();
@@ -246,8 +247,13 @@ public class ReadAheadInputStream extends InputStream {
@Override
public int read() throws IOException {
- byte[] oneByteArray = oneByte.get();
- return read(oneByteArray, 0, 1) == -1 ? -1 : oneByteArray[0] & 0xFF;
+ if (activeBuffer.hasRemaining()) {
+ // short path - just get one byte.
+ return activeBuffer.get() & 0xFF;
+ } else {
+ byte[] oneByteArray = oneByte.get();
+ return read(oneByteArray, 0, 1) == -1 ? -1 : oneByteArray[0] & 0xFF;
+ }
}
@Override
@@ -258,54 +264,43 @@ public class ReadAheadInputStream extends InputStream {
if (len == 0) {
return 0;
}
- stateChangeLock.lock();
- try {
- return readInternal(b, offset, len);
- } finally {
- stateChangeLock.unlock();
- }
- }
- /**
- * flip the active and read ahead buffer
- */
- private void swapBuffers() {
- ByteBuffer temp = activeBuffer;
- activeBuffer = readAheadBuffer;
- readAheadBuffer = temp;
- }
-
- /**
- * Internal read function which should be called only from read() api. The assumption is that
- * the stateChangeLock is already acquired in the caller before calling this function.
- */
- private int readInternal(byte[] b, int offset, int len) throws IOException {
- assert (stateChangeLock.isLocked());
if (!activeBuffer.hasRemaining()) {
- waitForAsyncReadComplete();
- if (readAheadBuffer.hasRemaining()) {
- swapBuffers();
- } else {
- // The first read or activeBuffer is skipped.
- readAsync();
+ // No remaining in active buffer - lock and switch to write ahead buffer.
+ stateChangeLock.lock();
+ try {
waitForAsyncReadComplete();
- if (isEndOfStream()) {
- return -1;
+ if (!readAheadBuffer.hasRemaining()) {
+ // The first read.
+ readAsync();
+ waitForAsyncReadComplete();
+ if (isEndOfStream()) {
+ return -1;
+ }
}
+ // Swap the newly read read ahead buffer in place of empty active buffer.
swapBuffers();
+ // After swapping buffers, trigger another async read for read ahead buffer.
+ readAsync();
+ } finally {
+ stateChangeLock.unlock();
}
- } else {
- checkReadException();
}
len = Math.min(len, activeBuffer.remaining());
activeBuffer.get(b, offset, len);
- if (activeBuffer.remaining() <= readAheadThresholdInBytes && !readAheadBuffer.hasRemaining()) {
- readAsync();
- }
return len;
}
+ /**
+ * flip the active and read ahead buffer
+ */
+ private void swapBuffers() {
+ ByteBuffer temp = activeBuffer;
+ activeBuffer = readAheadBuffer;
+ readAheadBuffer = temp;
+ }
+
@Override
public int available() throws IOException {
stateChangeLock.lock();
@@ -323,6 +318,11 @@ public class ReadAheadInputStream extends InputStream {
if (n <= 0L) {
return 0L;
}
+ if (n <= activeBuffer.remaining()) {
+ // Only skipping from active buffer is sufficient
+ activeBuffer.position((int) n + activeBuffer.position());
+ return n;
+ }
stateChangeLock.lock();
long skipped;
try {
@@ -346,21 +346,14 @@ public class ReadAheadInputStream extends InputStream {
if (available() >= n) {
// we can skip from the internal buffers
int toSkip = (int) n;
- if (toSkip <= activeBuffer.remaining()) {
- // Only skipping from active buffer is sufficient
- activeBuffer.position(toSkip + activeBuffer.position());
- if (activeBuffer.remaining() <= readAheadThresholdInBytes
- && !readAheadBuffer.hasRemaining()) {
- readAsync();
- }
- return n;
- }
// We need to skip from both active buffer and read ahead buffer
toSkip -= activeBuffer.remaining();
+ assert(toSkip > 0); // skipping from activeBuffer already handled.
activeBuffer.position(0);
activeBuffer.flip();
readAheadBuffer.position(toSkip + readAheadBuffer.position());
swapBuffers();
+ // Trigger async read to emptied read ahead buffer.
readAsync();
return n;
} else {
http://git-wip-us.apache.org/repos/asf/spark/blob/7539ae59/core/src/main/java/org/apache/spark/util/collection/unsafe/sort/UnsafeSorterSpillReader.java
----------------------------------------------------------------------
diff --git a/core/src/main/java/org/apache/spark/util/collection/unsafe/sort/UnsafeSorterSpillReader.java b/core/src/main/java/org/apache/spark/util/collection/unsafe/sort/UnsafeSorterSpillReader.java
index 2c53c8d..fb179d0 100644
--- a/core/src/main/java/org/apache/spark/util/collection/unsafe/sort/UnsafeSorterSpillReader.java
+++ b/core/src/main/java/org/apache/spark/util/collection/unsafe/sort/UnsafeSorterSpillReader.java
@@ -72,21 +72,15 @@ public final class UnsafeSorterSpillReader extends UnsafeSorterIterator implemen
bufferSizeBytes = DEFAULT_BUFFER_SIZE_BYTES;
}
- final double readAheadFraction =
- SparkEnv.get() == null ? 0.5 :
- SparkEnv.get().conf().getDouble("spark.unsafe.sorter.spill.read.ahead.fraction", 0.5);
-
- // SPARK-23310: Disable read-ahead input stream, because it is causing lock contention and perf
- // regression for TPC-DS queries.
final boolean readAheadEnabled = SparkEnv.get() != null &&
- SparkEnv.get().conf().getBoolean("spark.unsafe.sorter.spill.read.ahead.enabled", false);
+ SparkEnv.get().conf().getBoolean("spark.unsafe.sorter.spill.read.ahead.enabled", true);
final InputStream bs =
new NioBufferedFileInputStream(file, (int) bufferSizeBytes);
try {
if (readAheadEnabled) {
this.in = new ReadAheadInputStream(serializerManager.wrapStream(blockId, bs),
- (int) bufferSizeBytes, (int) (bufferSizeBytes * readAheadFraction));
+ (int) bufferSizeBytes);
} else {
this.in = serializerManager.wrapStream(blockId, bs);
}
http://git-wip-us.apache.org/repos/asf/spark/blob/7539ae59/core/src/test/java/org/apache/spark/io/GenericFileInputStreamSuite.java
----------------------------------------------------------------------
diff --git a/core/src/test/java/org/apache/spark/io/GenericFileInputStreamSuite.java b/core/src/test/java/org/apache/spark/io/GenericFileInputStreamSuite.java
index 3440e1a..22db359 100644
--- a/core/src/test/java/org/apache/spark/io/GenericFileInputStreamSuite.java
+++ b/core/src/test/java/org/apache/spark/io/GenericFileInputStreamSuite.java
@@ -37,7 +37,7 @@ public abstract class GenericFileInputStreamSuite {
protected File inputFile;
- protected InputStream inputStream;
+ protected InputStream[] inputStreams;
@Before
public void setUp() throws IOException {
@@ -54,77 +54,91 @@ public abstract class GenericFileInputStreamSuite {
@Test
public void testReadOneByte() throws IOException {
- for (int i = 0; i < randomBytes.length; i++) {
- assertEquals(randomBytes[i], (byte) inputStream.read());
+ for (InputStream inputStream: inputStreams) {
+ for (int i = 0; i < randomBytes.length; i++) {
+ assertEquals(randomBytes[i], (byte) inputStream.read());
+ }
}
}
@Test
public void testReadMultipleBytes() throws IOException {
- byte[] readBytes = new byte[8 * 1024];
- int i = 0;
- while (i < randomBytes.length) {
- int read = inputStream.read(readBytes, 0, 8 * 1024);
- for (int j = 0; j < read; j++) {
- assertEquals(randomBytes[i], readBytes[j]);
- i++;
+ for (InputStream inputStream: inputStreams) {
+ byte[] readBytes = new byte[8 * 1024];
+ int i = 0;
+ while (i < randomBytes.length) {
+ int read = inputStream.read(readBytes, 0, 8 * 1024);
+ for (int j = 0; j < read; j++) {
+ assertEquals(randomBytes[i], readBytes[j]);
+ i++;
+ }
}
}
}
@Test
public void testBytesSkipped() throws IOException {
- assertEquals(1024, inputStream.skip(1024));
- for (int i = 1024; i < randomBytes.length; i++) {
- assertEquals(randomBytes[i], (byte) inputStream.read());
+ for (InputStream inputStream: inputStreams) {
+ assertEquals(1024, inputStream.skip(1024));
+ for (int i = 1024; i < randomBytes.length; i++) {
+ assertEquals(randomBytes[i], (byte) inputStream.read());
+ }
}
}
@Test
public void testBytesSkippedAfterRead() throws IOException {
- for (int i = 0; i < 1024; i++) {
- assertEquals(randomBytes[i], (byte) inputStream.read());
- }
- assertEquals(1024, inputStream.skip(1024));
- for (int i = 2048; i < randomBytes.length; i++) {
- assertEquals(randomBytes[i], (byte) inputStream.read());
+ for (InputStream inputStream: inputStreams) {
+ for (int i = 0; i < 1024; i++) {
+ assertEquals(randomBytes[i], (byte) inputStream.read());
+ }
+ assertEquals(1024, inputStream.skip(1024));
+ for (int i = 2048; i < randomBytes.length; i++) {
+ assertEquals(randomBytes[i], (byte) inputStream.read());
+ }
}
}
@Test
public void testNegativeBytesSkippedAfterRead() throws IOException {
- for (int i = 0; i < 1024; i++) {
- assertEquals(randomBytes[i], (byte) inputStream.read());
- }
- // Skipping negative bytes should essential be a no-op
- assertEquals(0, inputStream.skip(-1));
- assertEquals(0, inputStream.skip(-1024));
- assertEquals(0, inputStream.skip(Long.MIN_VALUE));
- assertEquals(1024, inputStream.skip(1024));
- for (int i = 2048; i < randomBytes.length; i++) {
- assertEquals(randomBytes[i], (byte) inputStream.read());
+ for (InputStream inputStream: inputStreams) {
+ for (int i = 0; i < 1024; i++) {
+ assertEquals(randomBytes[i], (byte) inputStream.read());
+ }
+ // Skipping negative bytes should essential be a no-op
+ assertEquals(0, inputStream.skip(-1));
+ assertEquals(0, inputStream.skip(-1024));
+ assertEquals(0, inputStream.skip(Long.MIN_VALUE));
+ assertEquals(1024, inputStream.skip(1024));
+ for (int i = 2048; i < randomBytes.length; i++) {
+ assertEquals(randomBytes[i], (byte) inputStream.read());
+ }
}
}
@Test
public void testSkipFromFileChannel() throws IOException {
- // Since the buffer is smaller than the skipped bytes, this will guarantee
- // we skip from underlying file channel.
- assertEquals(1024, inputStream.skip(1024));
- for (int i = 1024; i < 2048; i++) {
- assertEquals(randomBytes[i], (byte) inputStream.read());
- }
- assertEquals(256, inputStream.skip(256));
- assertEquals(256, inputStream.skip(256));
- assertEquals(512, inputStream.skip(512));
- for (int i = 3072; i < randomBytes.length; i++) {
- assertEquals(randomBytes[i], (byte) inputStream.read());
+ for (InputStream inputStream: inputStreams) {
+ // Since the buffer is smaller than the skipped bytes, this will guarantee
+ // we skip from underlying file channel.
+ assertEquals(1024, inputStream.skip(1024));
+ for (int i = 1024; i < 2048; i++) {
+ assertEquals(randomBytes[i], (byte) inputStream.read());
+ }
+ assertEquals(256, inputStream.skip(256));
+ assertEquals(256, inputStream.skip(256));
+ assertEquals(512, inputStream.skip(512));
+ for (int i = 3072; i < randomBytes.length; i++) {
+ assertEquals(randomBytes[i], (byte) inputStream.read());
+ }
}
}
@Test
public void testBytesSkippedAfterEOF() throws IOException {
- assertEquals(randomBytes.length, inputStream.skip(randomBytes.length + 1));
- assertEquals(-1, inputStream.read());
+ for (InputStream inputStream: inputStreams) {
+ assertEquals(randomBytes.length, inputStream.skip(randomBytes.length + 1));
+ assertEquals(-1, inputStream.read());
+ }
}
}
http://git-wip-us.apache.org/repos/asf/spark/blob/7539ae59/core/src/test/java/org/apache/spark/io/NioBufferedInputStreamSuite.java
----------------------------------------------------------------------
diff --git a/core/src/test/java/org/apache/spark/io/NioBufferedInputStreamSuite.java b/core/src/test/java/org/apache/spark/io/NioBufferedInputStreamSuite.java
index 211b33a..a320f86 100644
--- a/core/src/test/java/org/apache/spark/io/NioBufferedInputStreamSuite.java
+++ b/core/src/test/java/org/apache/spark/io/NioBufferedInputStreamSuite.java
@@ -18,6 +18,7 @@ package org.apache.spark.io;
import org.junit.Before;
+import java.io.InputStream;
import java.io.IOException;
/**
@@ -28,6 +29,9 @@ public class NioBufferedInputStreamSuite extends GenericFileInputStreamSuite {
@Before
public void setUp() throws IOException {
super.setUp();
- inputStream = new NioBufferedFileInputStream(inputFile);
+ inputStreams = new InputStream[] {
+ new NioBufferedFileInputStream(inputFile), // default
+ new NioBufferedFileInputStream(inputFile, 123) // small, unaligned buffer
+ };
}
}
http://git-wip-us.apache.org/repos/asf/spark/blob/7539ae59/core/src/test/java/org/apache/spark/io/ReadAheadInputStreamSuite.java
----------------------------------------------------------------------
diff --git a/core/src/test/java/org/apache/spark/io/ReadAheadInputStreamSuite.java b/core/src/test/java/org/apache/spark/io/ReadAheadInputStreamSuite.java
index 918ddc4..bfa1e0b 100644
--- a/core/src/test/java/org/apache/spark/io/ReadAheadInputStreamSuite.java
+++ b/core/src/test/java/org/apache/spark/io/ReadAheadInputStreamSuite.java
@@ -19,16 +19,27 @@ package org.apache.spark.io;
import org.junit.Before;
import java.io.IOException;
+import java.io.InputStream;
/**
- * Tests functionality of {@link NioBufferedFileInputStream}
+ * Tests functionality of {@link ReadAheadInputStreamSuite}
*/
public class ReadAheadInputStreamSuite extends GenericFileInputStreamSuite {
@Before
public void setUp() throws IOException {
super.setUp();
- inputStream = new ReadAheadInputStream(
- new NioBufferedFileInputStream(inputFile), 8 * 1024, 4 * 1024);
+ inputStreams = new InputStream[] {
+ // Tests equal and aligned buffers of wrapped an outer stream.
+ new ReadAheadInputStream(new NioBufferedFileInputStream(inputFile, 8 * 1024), 8 * 1024),
+ // Tests aligned buffers, wrapped bigger than outer.
+ new ReadAheadInputStream(new NioBufferedFileInputStream(inputFile, 3 * 1024), 2 * 1024),
+ // Tests aligned buffers, wrapped smaller than outer.
+ new ReadAheadInputStream(new NioBufferedFileInputStream(inputFile, 2 * 1024), 3 * 1024),
+ // Tests unaligned buffers, wrapped bigger than outer.
+ new ReadAheadInputStream(new NioBufferedFileInputStream(inputFile, 321), 123),
+ // Tests unaligned buffers, wrapped smaller than outer.
+ new ReadAheadInputStream(new NioBufferedFileInputStream(inputFile, 123), 321)
+ };
}
}
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