apache/hadoop · error · RuntimeException

next value iterator interrupted

Error message

next value iterator interrupted

What it means

ValueIterator.next() wraps an InterruptedException from nextKeyValue() as RuntimeException('next value iterator interrupted', ie) because java.util.Iterator cannot throw checked exceptions. It almost always accompanies the task being stopped — speculative-kill victim, preemption, or JVM shutdown — rather than a user bug.

Source

Thrown at hadoop-mapreduce-project/hadoop-mapreduce-client/hadoop-mapreduce-client-core/src/main/java/org/apache/hadoop/mapreduce/task/ReduceContextImpl.java:245

      // if this is the first record, we don't need to advance
      if (firstValue) {
        firstValue = false;
        return value;
      }
      // if this isn't the first record and the next key is different, they
      // can't advance it here.
      if (!nextKeyIsSame) {
        throw new NoSuchElementException("iterate past last value");
      }
      // otherwise, go to the next key/value pair
      try {
        nextKeyValue();
        return value;
      } catch (IOException ie) {
        throw new RuntimeException("next value iterator failed", ie);
      } catch (InterruptedException ie) {
        // this is bad, but we can't modify the exception list of java.util
        throw new RuntimeException("next value iterator interrupted", ie);        
      }
    }

    @Override
    public void remove() {
      throw new UnsupportedOperationException("remove not implemented");
    }

    @Override
    public void mark() throws IOException {
      if (getBackupStore() == null) {
        backupStore = new BackupStore<KEYIN,VALUEIN>(conf, taskid);
      }
      isMarked = true;
      if (!inReset) {
        backupStore.reinitialize();
        if (currentKeyLength == -1) {
          // The user has not called next() for this iterator yet, so

View on GitHub (pinned to 2add963021)

Solutions

1. Check AM/RM logs for why the task was stopped (speculation, preemption) — the interrupt is the symptom
2. If frequent, tune down mapreduce.map.speculative / mapreduce.reduce.speculative or scheduler preemption settings
3. Do not swallow interrupts in custom Writable readFields implementations

try {
  reduce(key, context);
} catch (RuntimeException e) {
  if (e.getCause() instanceof InterruptedException) {
    Thread.currentThread().interrupt(); // restore and exit cleanly
    return;
  }
  throw e;
}

When it happens

Trigger: The task runner interrupts the reducer thread: the task lost a speculative race, containers are preempted by the scheduler, or the job was killed while the reducer was reading records.

Common situations: Speculative execution enabled on straggler-prone clusters; YARN preemption hitting reduce containers; operators killing jobs during long reduce phases.

Related errors

• Invoking cleanUpPartialOutputForTask() from non @Preemptable
• Failed to delete {pTask}
• hasNext failed
• next value iterator failed
• iterate past last value

AI-assisted analysis of apache/hadoop@2add963021 (2026-08-22). Data as JSON: /api/errors/49275a165bf38ff0. Report an issue: GitHub.