[YARN-2958] RMStateStore seems to unnecessarily and wrongly store sequence number separately

• Type: Bug
• Status: Closed
• Priority: Blocker
• Resolution: Fixed
• Fix Version/s: 2.7.0
• Component/s: resourcemanager
• Target Version/s: 2.7.0
• Hadoop Flags: Reviewed
• Assignee: Varun Saxena
• Reporter: Zhijie Shen
• Created: 13/Dec/14 00:18
• Updated: 10/Apr/15 20:09
• Resolved: 05/Jan/15 21:36

Description

It seems that RMStateStore updates last sequence number when storing or updating each individual DT, to recover the latest sequence number when RM restarting.

First, the current logic seems to be problematic:

  public synchronized void updateRMDelegationTokenAndSequenceNumber(
      RMDelegationTokenIdentifier rmDTIdentifier, Long renewDate,
      int latestSequenceNumber) {
    if(isFencedState()) {
      LOG.info("State store is in Fenced state. Can't update RM Delegation Token.");
      return;
    }
    try {
      updateRMDelegationTokenAndSequenceNumberInternal(rmDTIdentifier, renewDate,
          latestSequenceNumber);
    } catch (Exception e) {
      notifyStoreOperationFailed(e);
    }
  }

  @Override
  protected void updateStoredToken(RMDelegationTokenIdentifier id,
      long renewDate) {
    try {
      LOG.info("updating RMDelegation token with sequence number: "
          + id.getSequenceNumber());
      rmContext.getStateStore().updateRMDelegationTokenAndSequenceNumber(id,
        renewDate, id.getSequenceNumber());
    } catch (Exception e) {
      LOG.error("Error in updating persisted RMDelegationToken with sequence number: "
            + id.getSequenceNumber());
      ExitUtil.terminate(1, e);
    }
  }

According to code above, even when renewing a DT, the last sequence number is updated in the store, which is wrong. For example, we have the following sequence:
1. Get DT 1 (seq = 1)
2. Get DT 2( seq = 2)
3. Renew DT 1 (seq = 1)
4. Restart RM
The stored and then recovered last sequence number is 1. It makes the next created DT after RM restarting will conflict with DT 2 on sequence num.

Second, the aforementioned bug doesn't happen actually, because the recovered last sequence num has been overwritten at by the correctly one.

  public void recover(RMState rmState) throws Exception {

    LOG.info("recovering RMDelegationTokenSecretManager.");
    // recover RMDTMasterKeys
    for (DelegationKey dtKey : rmState.getRMDTSecretManagerState()
      .getMasterKeyState()) {
      addKey(dtKey);
    }

    // recover RMDelegationTokens
    Map<RMDelegationTokenIdentifier, Long> rmDelegationTokens =
        rmState.getRMDTSecretManagerState().getTokenState();
    this.delegationTokenSequenceNumber =
        rmState.getRMDTSecretManagerState().getDTSequenceNumber();
    for (Map.Entry<RMDelegationTokenIdentifier, Long> entry : rmDelegationTokens
      .entrySet()) {
      addPersistedDelegationToken(entry.getKey(), entry.getValue());
    }
  }

The code above recovers delegationTokenSequenceNumber by reading the last sequence number in the store. It could be wrong. Fortunately, delegationTokenSequenceNumber updates it to the right number.

    if (identifier.getSequenceNumber() > getDelegationTokenSeqNum()) {
      setDelegationTokenSeqNum(identifier.getSequenceNumber());
    }

All the stored identifiers will be gone through, and delegationTokenSequenceNumber will be set to the largest sequence number among these identifiers. Therefore, new DT will be assigned a sequence number which is always larger than that of all the recovered DT.

To sum up, two negatives make a positive, but it's good to fix the issue. Please let me know if I've missed something here.