[GitHub] [parquet-mr] parthchandra commented on a diff in pull request #968: PARQUET-2149: Async IO implementation for ParquetFileReader

[GitBox <gi...@apache.org>]

parthchandra commented on code in PR #968:
URL: https://github.com/apache/parquet-mr/pull/968#discussion_r876197602


##########
parquet-column/src/main/java/org/apache/parquet/column/page/PageReader.java:
##########
@@ -37,4 +39,9 @@ public interface PageReader {
    * @return the next page in that chunk or null if after the last page
    */
   DataPage readPage();
+
+  /**
+   * Close the page reader. By default it is no-op.
+   */
+  default void close() throws IOException {}

Review Comment:
   Sure.



##########
parquet-common/src/main/java/org/apache/parquet/bytes/AsyncMultiBufferInputStream.java:
##########
@@ -0,0 +1,173 @@
+/*
+ *  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
+ *
+ *    http://www.apache.org/licenses/LICENSE-2.0
+ *
+ *  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.parquet.bytes;
+
+import java.io.IOException;
+import java.nio.ByteBuffer;
+import java.util.List;
+import java.util.concurrent.ExecutorService;
+import java.util.concurrent.Future;
+import java.util.concurrent.LinkedBlockingQueue;
+import java.util.concurrent.TimeUnit;
+import java.util.concurrent.atomic.LongAccumulator;
+import java.util.concurrent.atomic.LongAdder;
+import org.apache.parquet.io.SeekableInputStream;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+class AsyncMultiBufferInputStream extends MultiBufferInputStream {
+
+  private static final Logger LOG = LoggerFactory.getLogger(AsyncMultiBufferInputStream.class);
+
+  final SeekableInputStream fileInputStream;
+  int fetchIndex = 0;
+  int readIndex = 0;
+  ExecutorService threadPool;
+  LinkedBlockingQueue<Future<Void>> readFutures;
+  boolean closed = false;
+  Exception ioException;
+
+  LongAdder totalTimeBlocked = new LongAdder();
+  LongAdder totalCountBlocked = new LongAdder();
+  LongAccumulator maxTimeBlocked = new LongAccumulator(Long::max, 0L);
+
+  AsyncMultiBufferInputStream(ExecutorService threadPool, SeekableInputStream fileInputStream,
+    List<ByteBuffer> buffers) {
+    super(buffers);
+    this.fileInputStream = fileInputStream;
+    this.threadPool = threadPool;
+    readFutures = new LinkedBlockingQueue<>(buffers.size());
+    if (LOG.isDebugEnabled()) {
+      LOG.debug("ASYNC: Begin read into buffers ");
+      for (ByteBuffer buf : buffers) {
+        LOG.debug("ASYNC: buffer {} ", buf);
+      }
+    }
+    fetchAll();
+  }
+
+  private void checkState() {
+    if (closed) {
+      throw new RuntimeException("Stream is closed");
+    }
+    synchronized (this) {
+      if (ioException != null) {
+        throw new RuntimeException(ioException);
+      }
+    }
+  }
+
+  private void fetchAll() {
+    checkState();
+    submitReadTask(0);
+  }
+
+  private void submitReadTask(int bufferNo) {
+    ByteBuffer buffer = buffers.get(bufferNo);
+    try {
+      readFutures.put(threadPool.submit(() -> {
+          readOneBuffer(buffer);
+          if (bufferNo < buffers.size() - 1) {
+            submitReadTask(bufferNo + 1);
+          }
+          return null;
+        })
+      );
+    } catch (InterruptedException e) {
+      Thread.currentThread().interrupt();
+      throw new RuntimeException(e);
+    }
+  }
+
+  private void readOneBuffer(ByteBuffer buffer) {
+    long startTime = System.nanoTime();
+    try {
+      fileInputStream.readFully(buffer);
+      buffer.flip();
+      long readCompleted = System.nanoTime();
+      long timeSpent = readCompleted - startTime;
+      LOG.debug("ASYNC Stream: READ - {}", timeSpent / 1000.0);
+      long putStart = System.nanoTime();
+      long putCompleted = System.nanoTime();
+      LOG.debug("ASYNC Stream: FS READ (output) BLOCKED - {}",
+        (putCompleted - putStart) / 1000.0);
+      fetchIndex++;
+    } catch (IOException e) {
+      // Save the exception so that the calling thread can check if something went wrong.
+      // checkState will throw an exception if the read task has failed.
+      synchronized(this) {
+        ioException = e;
+      }
+      throw new RuntimeException(e);
+    }
+  }
+
+  @Override
+  public boolean nextBuffer() {
+    checkState();
+    // hack: parent constructor can call this method before this class is fully initialized.
+    // Just return without doing anything.
+    if (readFutures == null) {
+      return false;
+    }

Review Comment:
   Glad you made me look. The synchronization was needed because I was saving any exception that might have occurred in the reader thread. However, that exception will be captured by the Future object and thrown as an ExecutionException when `Future,get` is called in line 135. 
   So we don't really need to save the exception and the synchronization around it can also be removed.



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