anujmodi2021 commented on code in PR #7832:
URL: https://github.com/apache/hadoop/pull/7832#discussion_r2467897734


##########
hadoop-tools/hadoop-azure/src/main/java/org/apache/hadoop/fs/azurebfs/services/ReadBufferManagerV2.java:
##########
@@ -106,123 +166,731 @@ void init() {
         executorServiceKeepAliveTimeInMilliSec,
         TimeUnit.MILLISECONDS,
         new SynchronousQueue<>(),
-        namedThreadFactory);
+        workerThreadFactory);
     workerPool.allowCoreThreadTimeOut(true);
     for (int i = 0; i < minThreadPoolSize; i++) {
-      ReadBufferWorker worker = new ReadBufferWorker(i, this);
+      ReadBufferWorker worker = new ReadBufferWorker(i, getBufferManager());
+      workerRefs.add(worker);
       workerPool.submit(worker);
     }
     ReadBufferWorker.UNLEASH_WORKERS.countDown();
+
+    if (isDynamicScalingEnabled) {
+      cpuMonitorThread = Executors.newSingleThreadScheduledExecutor(runnable 
-> {
+        Thread t = new Thread(runnable, "ReadAheadV2-CPU-Monitor");
+        t.setDaemon(true);
+        return t;
+      });
+      cpuMonitorThread.scheduleAtFixedRate(this::adjustThreadPool,
+          getCpuMonitoringIntervalInMilliSec(), 
getCpuMonitoringIntervalInMilliSec(),
+          TimeUnit.MILLISECONDS);
+    }
+
+    printTraceLog("ReadBufferManagerV2 initialized with {} buffers and {} 
worker threads",

Review Comment:
   Its a intentional method created to avoid code redundancy



##########
hadoop-tools/hadoop-azure/src/main/java/org/apache/hadoop/fs/azurebfs/services/ReadBufferManagerV2.java:
##########
@@ -17,67 +17,91 @@
  */
 package org.apache.hadoop.fs.azurebfs.services;
 
+import org.apache.hadoop.fs.azurebfs.AbfsConfiguration;
+import org.apache.hadoop.fs.azurebfs.contracts.services.ReadBufferStatus;
+
+import com.sun.management.OperatingSystemMXBean;
+
 import java.io.IOException;
+import java.lang.management.ManagementFactory;
+import java.lang.management.MemoryMXBean;
+import java.lang.management.MemoryUsage;
+import java.util.ArrayList;
+import java.util.Collection;
+import java.util.Iterator;
+import java.util.LinkedList;
+import java.util.List;
+import java.util.Stack;
+import java.util.concurrent.CountDownLatch;
+import java.util.concurrent.Executors;
+import java.util.concurrent.ScheduledExecutorService;
 import java.util.concurrent.SynchronousQueue;
 import java.util.concurrent.ThreadFactory;
 import java.util.concurrent.ThreadPoolExecutor;
 import java.util.concurrent.TimeUnit;
+import java.util.concurrent.locks.ReentrantLock;
 
-import org.apache.hadoop.classification.VisibleForTesting;
-import org.apache.hadoop.fs.azurebfs.AbfsConfiguration;
-import org.apache.hadoop.fs.azurebfs.contracts.services.ReadBufferStatus;
 import org.apache.hadoop.fs.azurebfs.utils.TracingContext;
+import org.apache.hadoop.classification.VisibleForTesting;
 
-final class ReadBufferManagerV2 extends ReadBufferManager {
+import static 
org.apache.hadoop.fs.azurebfs.constants.FileSystemConfigurations.ONE_HUNDRED;
+
+/**
+ * The Improved Read Buffer Manager for Rest AbfsClient.
+ */
+public class ReadBufferManagerV2 extends ReadBufferManager {
+  // Internal constants
+  private static final ReentrantLock LOCK = new ReentrantLock();
 
   // Thread Pool Configurations
   private static int minThreadPoolSize;
   private static int maxThreadPoolSize;
+  private static int cpuMonitoringIntervalInMilliSec;
+  private static double cpuThreshold;
+  private static int threadPoolUpscalePercentage;
+  private static int threadPoolDownscalePercentage;
   private static int executorServiceKeepAliveTimeInMilliSec;
+  private static final double THREAD_POOL_REQUIREMENT_BUFFER = 1.2; // 20% 
more threads than the queue size
+  private static boolean isDynamicScalingEnabled;
+
+  private ScheduledExecutorService cpuMonitorThread;
   private ThreadPoolExecutor workerPool;
+  private final List<ReadBufferWorker> workerRefs = new ArrayList<>();
 
   // Buffer Pool Configurations
   private static int minBufferPoolSize;
   private static int maxBufferPoolSize;
+  private static int memoryMonitoringIntervalInMilliSec;
+  private static double memoryThreshold;
+
   private int numberOfActiveBuffers = 0;
   private byte[][] bufferPool;
+  private Stack<Integer> removedBufferList = new Stack<>();
+  private ScheduledExecutorService memoryMonitorThread;
 
+  // Buffer Manager Structures
   private static ReadBufferManagerV2 bufferManager;
-
-  // hide instance constructor
-  private ReadBufferManagerV2() {
-    LOGGER.trace("Creating readbuffer manager with HADOOP-18546 patch");
-  }
+  private static boolean isConfigured = false;
 
   /**
-   * Sets the read buffer manager configurations.
-   * @param readAheadBlockSize the size of the read-ahead block in bytes
-   * @param abfsConfiguration the AbfsConfiguration instance for other 
configurations
+   * Private constructor to prevent instantiation as this needs to be 
singleton.
    */
-  static void setReadBufferManagerConfigs(int readAheadBlockSize, 
AbfsConfiguration abfsConfiguration) {
-    if (bufferManager == null) {
-      minThreadPoolSize = abfsConfiguration.getMinReadAheadV2ThreadPoolSize();
-      maxThreadPoolSize = abfsConfiguration.getMaxReadAheadV2ThreadPoolSize();
-      executorServiceKeepAliveTimeInMilliSec = 
abfsConfiguration.getReadAheadExecutorServiceTTLInMillis();
-
-      minBufferPoolSize = abfsConfiguration.getMinReadAheadV2BufferPoolSize();
-      maxBufferPoolSize = abfsConfiguration.getMaxReadAheadV2BufferPoolSize();
-      
setThresholdAgeMilliseconds(abfsConfiguration.getReadAheadV2CachedBufferTTLMillis());
-      setReadAheadBlockSize(readAheadBlockSize);
-    }
+  private ReadBufferManagerV2() {
+    printTraceLog("Creating Read Buffer Manager V2 with HADOOP-18546 patch");

Review Comment:
   Its same only. Just a method call to avoid redundant checks on log



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