SteNicholas commented on code in PR #3858:
URL: https://github.com/apache/celeborn/pull/3858#discussion_r4444775434


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worker/src/main/scala/org/apache/celeborn/service/deploy/worker/metrics/DefaultScaleMetricCollector.scala:
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@@ -0,0 +1,111 @@
+/*
+ * 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.celeborn.service.deploy.worker.metrics
+
+import java.lang.management.{ManagementFactory, OperatingSystemMXBean}
+import java.util.concurrent.{ScheduledFuture, TimeUnit}
+
+import scala.util.control.NonFatal
+
+import org.apache.celeborn.common.CelebornConf
+import org.apache.celeborn.common.internal.Logging
+import org.apache.celeborn.common.metrics.WorkerStats
+import org.apache.celeborn.common.util.{DiskUtils, ThreadUtils}
+import org.apache.celeborn.service.deploy.worker.Worker
+
+class DefaultScaleMetricCollector private[metrics] (
+    conf: CelebornConf,
+    operatingSystem: OperatingSystemMXBean)
+  extends ScaleMetricCollector with Logging {
+
+  def this(conf: CelebornConf) =
+    this(conf, ManagementFactory.getOperatingSystemMXBean)
+
+  private val memoryWindow = new 
MetricSlidingWindow(conf.scaleMetricMemoryWindowSize)
+  private val executor =
+    
ThreadUtils.newDaemonSingleThreadScheduledExecutor("scale-metric-collector")
+  private var scheduledTask: ScheduledFuture[_] = _
+
+  @volatile private var stopped = false
+  @volatile private var currentStats: Option[WorkerStats] = None
+
+  override def init(worker: Worker): Unit = synchronized {
+    require(!stopped && scheduledTask == null, "Metric collector can only be 
initialized once")
+    scheduledTask = executor.scheduleWithFixedDelay(
+      new Runnable {
+        override def run(): Unit = collectOnce(worker)
+      },
+      conf.scaleMetricInterval,
+      conf.scaleMetricInterval,
+      TimeUnit.MILLISECONDS)
+  }
+
+  override def stop(): Unit = synchronized {
+    stopped = true
+    currentStats = None
+    if (scheduledTask != null) {
+      scheduledTask.cancel(true)
+    }
+    executor.shutdownNow()
+  }
+
+  override def currentWorkerStats(): Option[WorkerStats] = {
+    if (stopped) None
+    else currentStats
+  }
+
+  private[metrics] def collectOnce(worker: Worker): Unit = {
+    try {
+      val metrics = memoryMetrics(worker) ++ systemLoadMetrics() ++ 
diskMetrics(worker)
+      currentStats = Some(WorkerStats(metrics))
+    } catch {
+      case NonFatal(e) =>
+        logWarning("Failed to collect worker scaling metrics", e)
+    }
+  }
+
+  private def memoryMetrics(worker: Worker): Map[String, Double] = {
+    val capacity = worker.memoryManager.maxDirectMemory
+    val used = worker.memoryManager.getMemoryUsage
+    memoryWindow.update(used)
+    Map(WorkerStats.NettyMemoryUsedRatio -> (memoryWindow.average / capacity))

Review Comment:
   **Align the memory metric name with its numerator**: 
`MemoryManager.getMemoryUsage()` returns `getNettyUsedDirectMemory() + 
sortMemoryCounter.get()`, so this reports combined memory pressure under the 
name `NettyMemoryUsedRatio`. When sorting reserves memory, the reported value 
can rise without Netty usage increasing, making the metric misleading for 
consumers and comparisons with the existing `NettyMemory` gauge.
   
   If the combined accounting is intended, could we rename the metric to 
something such as `DirectMemoryUsedRatio` and update the configuration 
documentation and tests? If it is intended to measure only Netty usage, the 
numerator should use `getNettyUsedDirectMemory()` instead.



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