apache/hadoop · error · IllegalArgumentException

ns + "." + IPC_CALLQUEUE_WRRMUX_WEIGHTS_KEY + " must specify

Error message

ns + "." + IPC_CALLQUEUE_WRRMUX_WEIGHTS_KEY + " must specify exactly " + this.numQueues + " weights: one for each priority level."

What it means

When ipc.<port>.callqueue.faircallqueue.multiplexer.weights (ns + '.' + IPC_CALLQUEUE_WRRMUX_WEIGHTS_KEY) is set, the number of comma-separated integers must exactly equal the number of priority queues — one weight per queue. If the counts differ, the constructor throws IllegalArgumentException and the server fails to start. When the key is unset, defaults (powers of two, 2^N) are generated automatically.

Source

Thrown at hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/ipc/WeightedRoundRobinMultiplexer.java:70

  private final AtomicInteger requestsLeft; // Number of requests left for this queue

  private int[] queueWeights; // The weights for each queue

  public WeightedRoundRobinMultiplexer(int aNumQueues, String ns,
    Configuration conf) {
    if (aNumQueues <= 0) {
      throw new IllegalArgumentException("Requested queues (" + aNumQueues +
        ") must be greater than zero.");
    }

    this.numQueues = aNumQueues;
    this.queueWeights = conf.getInts(ns + "." +
      IPC_CALLQUEUE_WRRMUX_WEIGHTS_KEY);

    if (this.queueWeights.length == 0) {
      this.queueWeights = getDefaultQueueWeights(this.numQueues);
    } else if (this.queueWeights.length != this.numQueues) {
      throw new IllegalArgumentException(ns + "." +
        IPC_CALLQUEUE_WRRMUX_WEIGHTS_KEY + " must specify exactly " +
        this.numQueues + " weights: one for each priority level.");
    }

    this.currentQueueIndex = new AtomicInteger(0);
    this.requestsLeft = new AtomicInteger(this.queueWeights[0]);

    LOG.info("WeightedRoundRobinMultiplexer is being used.");
  }

  /**
   * Creates default weights for each queue. The weights are 2^N.
   */
  private int[] getDefaultQueueWeights(int aNumQueues) {
    int[] weights = new int[aNumQueues];

    int weight = 1; // Start low
    for(int i = aNumQueues - 1; i >= 0; i--) { // Start at lowest queue

View on GitHub (pinned to 2add963021)

Solutions

1. Count your priority levels and provide exactly that many weights, e.g. for 3 queues: ipc.8020.callqueue.faircallqueue.multiplexer.weights=9,4,1.
2. Or delete the weights key entirely to accept the default 2^N weights.
3. Re-check the value after any change to priority-levels / scheduler priority-levels — the two settings must move together.

Example fix

# before (3 weights but 4 priority levels)
ipc.8020.callqueue.priority-levels=4
ipc.8020.callqueue.faircallqueue.multiplexer.weights=9,4,1

# after
ipc.8020.callqueue.priority-levels=3
ipc.8020.callqueue.faircallqueue.multiplexer.weights=9,4,1

int levels = conf.getInt("ipc." + port + ".callqueue.priority-levels", 4);
int[] weights = conf.getInts("ipc." + port + ".callqueue.faircallqueue.multiplexer.weights");
if (weights.length != 0 && weights.length != levels) {
  throw new IllegalArgumentException("weights count " + weights.length
      + " != priority levels " + levels + "; fix config before starting server");
}

When it happens

Trigger: Setting ipc.8020.callqueue.faircallqueue.multiplexer.weights=9,4,1 while priority-levels is 2 or 4 (count mismatch); editing priority-levels without updating the weights list; extra trailing comma producing an unexpected parsed entry.

Common situations: Call-queue tuning changes where operators change the number of queues but leave the old weights array; copy-pasted configs between services with different port namespaces and different queue counts.

Related errors

• "Requested queues (" + aNumQueues + ") must be greater than
• numLevels must be at least 1
• callqueue.capacity.weights must specify ${priorityLevels} ca
• callqueue.capacity.weights only takes positive weights. ${w}
• Illegal field separator: ${separator}

AI-assisted analysis of apache/hadoop@2add963021 (2026-08-22). Data as JSON: /api/errors/7a81eeb1ca5db107. Report an issue: GitHub.