apache/hadoop · warning · InvalidRequestException

{this}: invalid negative slot index {slotIdx}

Error message

{this}: invalid negative slot index {slotIdx}

What it means

registerSlot(slotIdx, blockId) runs on the datanode (ShortCircuitRegistry.registerSlot, called from DataXceiver) when a client that allocated a slot in the shared segment reports it while requesting short-circuit file descriptors. A negative index can never be valid - calculateSlotAddress would point before the mapping - so the datanode rejects it with InvalidRequestException. This is a protocol violation or corrupted request, not a tunable condition.

Source

Thrown at hadoop-hdfs-project/hadoop-hdfs-client/src/main/java/org/apache/hadoop/hdfs/shortcircuit/ShortCircuitShm.java:577

  }

  /**
   * Register a slot.
   *
   * This function looks at a slot which has already been initialized (by
   * another process), and registers it with us.  Then, it returns the
   * relevant Slot object.
   *
   * @return    The slot.
   *
   * @throws InvalidRequestException
   *            If the slot index we're trying to allocate has not been
   *            initialized, or is already in use.
   */
  synchronized public final Slot registerSlot(int slotIdx,
      ExtendedBlockId blockId) throws InvalidRequestException {
    if (slotIdx < 0) {
      throw new InvalidRequestException(this + ": invalid negative slot " +
          "index " + slotIdx);
    }
    if (slotIdx >= slots.length) {
      throw new InvalidRequestException(this + ": invalid slot " +
          "index " + slotIdx);
    }
    if (allocatedSlots.get(slotIdx)) {
      throw new InvalidRequestException(this + ": slot " + slotIdx +
          " is already in use.");
    }
    Slot slot = new Slot(calculateSlotAddress(slotIdx), blockId);
    if (!slot.isValid()) {
      throw new InvalidRequestException(this + ": slot " + slotIdx +
          " is not marked as valid.");
    }
    slots[slotIdx] = slot;
    allocatedSlots.set(slotIdx, true);
    if (LOG.isTraceEnabled()) {

View on GitHub (pinned to 2add963021)

Solutions

1. Verify client and datanode run the exact same Hadoop release
2. Reproduce with trace logging on org.apache.hadoop.hdfs.shortcircuit to capture the offending slot index
3. Restart the client to re-establish clean shm state
4. If it persists on stock software, file a Hadoop JIRA with the trace logs

// Client side: never hand-build SlotId values; only use indices returned by the shm layer
Slot slot = shm.allocAndRegisterSlot(blockId); // idx >= 0 guaranteed here

try {
  // datanode-side registration of client slots
} catch (InvalidRequestException e) {
  // reject the client request; client re-establishes a fresh shm
}

When it happens

Trigger: DataXceiver opRequestShortCircuitFds receiving a SlotId whose slot index is negative: a client-side bug, a corrupted slot id, or version skew where the two sides disagree on the slot id encoding.

Common situations: Mixing Hadoop versions across the short-circuit protocol; patched or custom client builds; essentially never seen on unmodified releases.

Related errors

• {this}: slot {slotIdx} does not exist.
• {this}: invalid slot index {slotIdx}
• {this}: slot {slotIdx} is already in use.
• {this}: no more slots are available.
• {this}: slot {slotIdx} is not marked as valid.

AI-assisted analysis of apache/hadoop@2add963021 (2026-08-22). Data as JSON: /api/errors/e59177999fbcca58. Report an issue: GitHub.