apache/hadoop · error · IllegalArgumentException

The bucket size in the rolling window is not integer: window

Error message

The bucket size in the rolling window is not integer: windowLenMs= {} numBuckets= {}

What it means

Error "The bucket size in the rolling window is not integer: windowLenMs= {} numBuckets= {}" thrown in apache/hadoop.

Source

Thrown at hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/namenode/top/window/RollingWindow.java:80

   */
  Bucket[] buckets;
  final int windowLenMs;
  final int bucketSize;

  /**
   * @param windowLenMs The period that is covered by the window. This period must
   *          be more than the buffering delays.
   * @param numBuckets number of buckets in the window
   */
  RollingWindow(int windowLenMs, int numBuckets) {
    buckets = new Bucket[numBuckets];
    for (int i = 0; i < numBuckets; i++) {
      buckets[i] = new Bucket();
    }
    this.windowLenMs = windowLenMs;
    this.bucketSize = windowLenMs / numBuckets;
    if (this.windowLenMs % numBuckets != 0) {
      throw new IllegalArgumentException(
          "The bucket size in the rolling window is not integer: windowLenMs= "
              + windowLenMs + " numBuckets= " + numBuckets);
    }
  }

  /**
   * When an event occurs at the specified time, this method reflects that in
   * the rolling window.
   * <p>
   *
   * @param time the time at which the event occurred
   * @param delta the delta that will be added to the window
   */
  public void incAt(long time, long delta) {
    int bi = computeBucketIndex(time);
    Bucket bucket = buckets[bi];
    // If the last time the bucket was updated is out of the scope of the
    // rolling window, reset the bucket.

View on GitHub (pinned to 2add963021)

Solutions

1. Choose a rolling window length that divides evenly into the configured number of buckets (windowLenMs % numBuckets == 0).

When it happens

Trigger: The top rolling window is configured with a window length not divisible by the bucket count.

Common situations: Setting dfs.namenode.top.window.num.buckets and window length to incompatible values.

AI-assisted analysis of apache/hadoop@2add963021 (2026-08-22). Data as JSON: /api/errors/84a872d8157d628f. Report an issue: GitHub.