private boolean versionDelete(DeleteUpdateCommand cmd) throws IOException {

    BytesRef idBytes = cmd.getIndexedId();

    if (vinfo == null || idBytes == null) {
      super.processDelete(cmd);
      return false;
    }

    // This is only the hash for the bucket, and must be based only on the uniqueKey (i.e. do not
    // use a pluggable hash here)
    int bucketHash = Hash.murmurhash3_x86_32(idBytes.bytes, idBytes.offset, idBytes.length, 0);

    // at this point, there is an update we need to try and apply.
    // we may or may not be the leader.

    // Find the version
    long versionOnUpdate = cmd.getVersion();
    if (versionOnUpdate == 0) {
      String versionOnUpdateS = req.getParams().get(VERSION_FIELD);
      versionOnUpdate = versionOnUpdateS == null ? 0 : Long.parseLong(versionOnUpdateS);
    }
    long signedVersionOnUpdate = versionOnUpdate;
    versionOnUpdate = Math.abs(versionOnUpdate); // normalize to positive version

    boolean isReplay = (cmd.getFlags() & UpdateCommand.REPLAY) != 0;
    boolean leaderLogic = isLeader && !isReplay;

    if (!leaderLogic && versionOnUpdate == 0) {
      throw new SolrException(ErrorCode.BAD_REQUEST, "missing _version_ on update from leader");
    }

    VersionBucket bucket = vinfo.bucket(bucketHash);

    vinfo.lockForUpdate();
    try {

      synchronized (bucket) {
        if (versionsStored) {
          long bucketVersion = bucket.highest;

          if (leaderLogic) {

            if (signedVersionOnUpdate != 0) {
              Long lastVersion = vinfo.lookupVersion(cmd.getIndexedId());
              long foundVersion = lastVersion == null ? -1 : lastVersion;
              if ((signedVersionOnUpdate == foundVersion)
                  || (signedVersionOnUpdate < 0 && foundVersion < 0)
                  || (signedVersionOnUpdate == 1 && foundVersion > 0)) {
                // we're ok if versions match, or if both are negative (all missing docs are equal),
                // or if cmd
                // specified it must exist (versionOnUpdate==1) and it does.
              } else {
                throw new SolrException(
                    ErrorCode.CONFLICT,
                    "version conflict for "
                        + cmd.getId()
                        + " expected="
                        + signedVersionOnUpdate
                        + " actual="
                        + foundVersion);
              }
            }

            long version = vinfo.getNewClock();
            cmd.setVersion(-version);
            bucket.updateHighest(version);
          } else {
            cmd.setVersion(-versionOnUpdate);

            if (ulog.getState() != UpdateLog.State.ACTIVE
                && (cmd.getFlags() & UpdateCommand.REPLAY) == 0) {
              // we're not in an active state, and this update isn't from a replay, so buffer it.
              cmd.setFlags(cmd.getFlags() | UpdateCommand.BUFFERING);
              ulog.delete(cmd);
              return true;
            }

            // if we aren't the leader, then we need to check that updates were not re-ordered
            if (bucketVersion != 0 && bucketVersion < versionOnUpdate) {
              // we're OK... this update has a version higher than anything we've seen
              // in this bucket so far, so we know that no reordering has yet occured.
              bucket.updateHighest(versionOnUpdate);
            } else {
              // there have been updates higher than the current update.  we need to check
              // the specific version for this id.
              Long lastVersion = vinfo.lookupVersion(cmd.getIndexedId());
              if (lastVersion != null && Math.abs(lastVersion) >= versionOnUpdate) {
                // This update is a repeat, or was reordered.  We need to drop this update.
                return true;
              }
            }
          }
        }

        doLocalDelete(cmd);
        return false;
      } // end synchronized (bucket)

    } finally {
      vinfo.unlockForUpdate();
    }
  }
  public void doDeleteByQuery(DeleteUpdateCommand cmd) throws IOException {
    // even in non zk mode, tests simulate updates from a leader
    if (!zkEnabled) {
      isLeader = getNonZkLeaderAssumption(req);
    } else {
      zkCheck();
    }

    // NONE: we are the first to receive this deleteByQuery
    //       - it must be forwarded to the leader of every shard
    // TO:   we are a leader receiving a forwarded deleteByQuery... we must:
    //       - block all updates (use VersionInfo)
    //       - flush *all* updates going to our replicas
    //       - forward the DBQ to our replicas and wait for the response
    //       - log + execute the local DBQ
    // FROM: we are a replica receiving a DBQ from our leader
    //       - log + execute the local DBQ
    DistribPhase phase = DistribPhase.parseParam(req.getParams().get(DISTRIB_UPDATE_PARAM));

    if (zkEnabled && DistribPhase.NONE == phase) {
      boolean leaderForAnyShard = false; // start off by assuming we are not a leader for any shard

      Map<String, Slice> slices = zkController.getClusterState().getSlices(collection);
      if (slices == null) {
        throw new SolrException(
            ErrorCode.BAD_REQUEST,
            "Cannot find collection:"
                + collection
                + " in "
                + zkController.getClusterState().getCollections());
      }

      ModifiableSolrParams params = new ModifiableSolrParams(filterParams(req.getParams()));
      params.set(DISTRIB_UPDATE_PARAM, DistribPhase.TOLEADER.toString());

      List<Node> leaders = new ArrayList<Node>(slices.size());
      for (Map.Entry<String, Slice> sliceEntry : slices.entrySet()) {
        String sliceName = sliceEntry.getKey();
        ZkNodeProps leaderProps;
        try {
          leaderProps = zkController.getZkStateReader().getLeaderProps(collection, sliceName);
        } catch (InterruptedException e) {
          throw new SolrException(
              ErrorCode.SERVICE_UNAVAILABLE, "Exception finding leader for shard " + sliceName, e);
        }

        // TODO: What if leaders changed in the meantime?
        // should we send out slice-at-a-time and if a node returns "hey, I'm not a leader" (or we
        // get an error because it went down) then look up the new leader?

        // Am I the leader for this slice?
        ZkCoreNodeProps coreLeaderProps = new ZkCoreNodeProps(leaderProps);
        String leaderNodeName = coreLeaderProps.getCoreNodeName();
        String coreName = req.getCore().getName();
        String coreNodeName = zkController.getNodeName() + "_" + coreName;
        isLeader = coreNodeName.equals(leaderNodeName);

        if (isLeader) {
          // don't forward to ourself
          leaderForAnyShard = true;
        } else {
          leaders.add(new StdNode(coreLeaderProps));
        }
      }

      params.remove("commit"); // this will be distributed from the local commit
      cmdDistrib.distribDelete(cmd, leaders, params);

      if (!leaderForAnyShard) {
        return;
      }

      // change the phase to TOLEADER so we look up and forward to our own replicas (if any)
      phase = DistribPhase.TOLEADER;
    }

    List<Node> replicas = null;

    if (zkEnabled && DistribPhase.TOLEADER == phase) {
      // This core should be a leader
      isLeader = true;
      replicas = setupRequest();
    } else if (DistribPhase.FROMLEADER == phase) {
      isLeader = false;
    }

    if (vinfo == null) {
      super.processDelete(cmd);
      return;
    }

    // at this point, there is an update we need to try and apply.
    // we may or may not be the leader.

    // Find the version
    long versionOnUpdate = cmd.getVersion();
    if (versionOnUpdate == 0) {
      String versionOnUpdateS = req.getParams().get(VERSION_FIELD);
      versionOnUpdate = versionOnUpdateS == null ? 0 : Long.parseLong(versionOnUpdateS);
    }
    versionOnUpdate = Math.abs(versionOnUpdate); // normalize to positive version

    boolean isReplay = (cmd.getFlags() & UpdateCommand.REPLAY) != 0;
    boolean leaderLogic = isLeader && !isReplay;

    if (!leaderLogic && versionOnUpdate == 0) {
      throw new SolrException(ErrorCode.BAD_REQUEST, "missing _version_ on update from leader");
    }

    vinfo.blockUpdates();
    try {

      if (versionsStored) {
        if (leaderLogic) {
          long version = vinfo.getNewClock();
          cmd.setVersion(-version);
          // TODO update versions in all buckets

          doLocalDelete(cmd);

        } else {
          cmd.setVersion(-versionOnUpdate);

          if (ulog.getState() != UpdateLog.State.ACTIVE
              && (cmd.getFlags() & UpdateCommand.REPLAY) == 0) {
            // we're not in an active state, and this update isn't from a replay, so buffer it.
            cmd.setFlags(cmd.getFlags() | UpdateCommand.BUFFERING);
            ulog.deleteByQuery(cmd);
            return;
          }

          doLocalDelete(cmd);
        }
      }

      // since we don't know which documents were deleted, the easiest thing to do is to invalidate
      // all real-time caches (i.e. UpdateLog) which involves also getting a new version of the
      // IndexReader
      // (so cache misses will see up-to-date data)

    } finally {
      vinfo.unblockUpdates();
    }

    // forward to all replicas
    if (leaderLogic && replicas != null) {
      ModifiableSolrParams params = new ModifiableSolrParams(filterParams(req.getParams()));
      params.set(VERSION_FIELD, Long.toString(cmd.getVersion()));
      params.set(DISTRIB_UPDATE_PARAM, DistribPhase.FROMLEADER.toString());
      params.set(
          "update.from",
          ZkCoreNodeProps.getCoreUrl(zkController.getBaseUrl(), req.getCore().getName()));
      cmdDistrib.distribDelete(cmd, replicas, params);
      cmdDistrib.finish();
    }

    if (returnVersions && rsp != null) {
      if (deleteByQueryResponse == null) {
        deleteByQueryResponse = new NamedList<String>();
        rsp.add("deleteByQuery", deleteByQueryResponse);
      }
      deleteByQueryResponse.add(cmd.getQuery(), cmd.getVersion());
    }
  }