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();
    }
  }
  /**
   * @return whether or not to drop this cmd
   * @throws IOException If there is a low-level I/O error.
   */
  private boolean versionAdd(AddUpdateCommand cmd) throws IOException {
    BytesRef idBytes = cmd.getIndexedId();

    if (vinfo == null || idBytes == null) {
      super.processAdd(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 any existing version in the document
    // TODO: don't reuse update commands any more!
    long versionOnUpdate = cmd.getVersion();

    if (versionOnUpdate == 0) {
      SolrInputField versionField = cmd.getSolrInputDocument().getField(VersionInfo.VERSION_FIELD);
      if (versionField != null) {
        Object o = versionField.getValue();
        versionOnUpdate =
            o instanceof Number ? ((Number) o).longValue() : Long.parseLong(o.toString());
      } else {
        // Find the version
        String versionOnUpdateS = req.getParams().get(VERSION_FIELD);
        versionOnUpdate = versionOnUpdateS == null ? 0 : Long.parseLong(versionOnUpdateS);
      }
    }

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

    VersionBucket bucket = vinfo.bucket(bucketHash);

    vinfo.lockForUpdate();
    try {
      synchronized (bucket) {
        // we obtain the version when synchronized and then do the add so we can ensure that
        // if version1 < version2 then version1 is actually added before version2.

        // even if we don't store the version field, synchronizing on the bucket
        // will enable us to know what version happened first, and thus enable
        // realtime-get to work reliably.
        // TODO: if versions aren't stored, do we need to set on the cmd anyway for some reason?
        // there may be other reasons in the future for a version on the commands

        boolean checkDeleteByQueries = false;

        if (versionsStored) {

          long bucketVersion = bucket.highest;

          if (leaderLogic) {

            boolean updated = getUpdatedDocument(cmd, versionOnUpdate);

            if (versionOnUpdate != 0) {
              Long lastVersion = vinfo.lookupVersion(cmd.getIndexedId());
              long foundVersion = lastVersion == null ? -1 : lastVersion;
              if (versionOnUpdate == foundVersion
                  || (versionOnUpdate < 0 && foundVersion < 0)
                  || (versionOnUpdate == 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.getPrintableId()
                        + " expected="
                        + versionOnUpdate
                        + " actual="
                        + foundVersion);
              }
            }

            long version = vinfo.getNewClock();
            cmd.setVersion(version);
            cmd.getSolrInputDocument().setField(VersionInfo.VERSION_FIELD, version);
            bucket.updateHighest(version);
          } else {
            // The leader forwarded us this update.
            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.add(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 occurred.
              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;
              }

              // also need to re-apply newer deleteByQuery commands
              checkDeleteByQueries = true;
            }
          }
        }

        boolean willDistrib = isLeader && nodes != null && nodes.size() > 0;

        SolrInputDocument clonedDoc = null;
        if (willDistrib) {
          clonedDoc = cmd.solrDoc.deepCopy();
        }

        // TODO: possibly set checkDeleteByQueries as a flag on the command?
        doLocalAdd(cmd);

        if (willDistrib) {
          cmd.solrDoc = clonedDoc;
        }
      } // end synchronized (bucket)
    } finally {
      vinfo.unlockForUpdate();
    }
    return false;
  }