[GitHub] [hive] pvary commented on a change in pull request #660: HIVE-21823: New metrics to get the average queue length / free executor number for a given time window

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pvary commented on a change in pull request #660: HIVE-21823: New metrics to get the average queue length / free executor number for a given time window
URL: https://github.com/apache/hive/pull/660#discussion_r290618110
 
 

 ##########
 File path: llap-server/src/java/org/apache/hadoop/hive/llap/metrics/LlapDaemonExecutorMetrics.java
 ##########
 @@ -397,4 +425,106 @@ public JvmMetrics getJvmMetrics() {
   public String getName() {
     return name;
   }
+
+  /**
+   * Generate time aware average for data points.
+   * For example if we have 3s when the queue size is 1, and 1s when the queue size is 2 then the
+   * calculated average should be (3*1+1*2)/4 = 1.25.
+   */
+  @VisibleForTesting
+  static class TimedAverageMetrics {
+    private final int windowDataSize;
+    private final long windowTimeSize;
+    private final Data[] data;
+    private int nextPos = 0;
+
+    /**
+     * Creates and initializes the metrics object.
+     * @param windowDataSize The maximum number of samples stored
+     * @param windowTimeSize The time window used to generate the average in nanoseconds
+     */
+    TimedAverageMetrics(int windowDataSize, long windowTimeSize) {
+      this(windowDataSize, windowTimeSize, System.nanoTime());
+    }
+
+    @VisibleForTesting
+    TimedAverageMetrics(int windowDataSize, long windowTimeSize,
+        long defaultTime) {
+      assert(windowDataSize > 0);
+      this.windowDataSize = windowDataSize;
+      this.windowTimeSize = windowTimeSize;
+      this.data = new Data[windowDataSize];
+      Arrays.setAll(data, i -> new Data(defaultTime, 0L));
+    }
+
+    /**
+     * Adds a new sample value to the metrics.
+     * @param value The new sample value
+     */
+    public synchronized void add(long value) {
+      add(System.nanoTime(), value);
+    }
+
+    /**
+     * Calculates the average for the last windowTimeSize window.
+     * @return The average
+     */
+    public synchronized long value() {
+      return value(System.nanoTime());
+    }
+
+    @VisibleForTesting
+    void add(long time, long value) {
+      data[nextPos].nanoTime = time;
+      data[nextPos].value = value;
+      nextPos++;
+      if (nextPos == windowDataSize) {
+        nextPos = 0;
+      }
+    }
+
+    @VisibleForTesting
+    long value(long time) {
+      // We expect that the data time positions are strictly increasing and the time is greater than
+      // any of the data position time. This is ensured by using System.nanoTime().
+      long sum = 0L;
+      long lastTime = time;
+      long minTime = lastTime - windowTimeSize;
+      int pos = nextPos - 1;
+      boolean firstRound = true;
+      while (firstRound || pos != nextPos - 1) {
 
 Review comment:
   Yeah... tried to add the last part in the loop, and forget to revert to the do while :D
   Done.

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