/** @param nodes Nodes. */
    private Queue<ClusterNode> fallbacks(Collection<ClusterNode> nodes) {
      Queue<ClusterNode> fallbacks = new LinkedList<>();

      ClusterNode node = F.first(F.view(nodes, IS_LOC_NODE));

      if (node != null) fallbacks.add(node);

      fallbacks.addAll(node != null ? F.view(nodes, F.not(IS_LOC_NODE)) : nodes);

      return fallbacks;
    }
  /**
   * @param cctx Cache context.
   * @param prj Projection (optional).
   * @return Collection of data nodes in provided projection (if any).
   */
  private static Collection<ClusterNode> nodes(
      final GridCacheContext<?, ?> cctx,
      @Nullable final ClusterGroup prj,
      @Nullable final Integer part) {
    assert cctx != null;

    final AffinityTopologyVersion topVer = cctx.affinity().affinityTopologyVersion();

    Collection<ClusterNode> affNodes = CU.affinityNodes(cctx);

    if (prj == null && part == null) return affNodes;

    final Set<ClusterNode> owners =
        part == null
            ? Collections.<ClusterNode>emptySet()
            : new HashSet<>(cctx.topology().owners(part, topVer));

    return F.view(
        affNodes,
        new P1<ClusterNode>() {
          @Override
          public boolean apply(ClusterNode n) {

            return cctx.discovery().cacheAffinityNode(n, cctx.name())
                && (prj == null || prj.node(n.id()) != null)
                && (part == null || owners.contains(n));
          }
        });
  }
  /** @return Nodes to execute on. */
  private Collection<ClusterNode> nodes() {
    CacheMode cacheMode = cctx.config().getCacheMode();

    switch (cacheMode) {
      case LOCAL:
        if (prj != null)
          U.warn(
              log,
              "Ignoring query projection because it's executed over LOCAL cache "
                  + "(only local node will be queried): "
                  + this);

        return Collections.singletonList(cctx.localNode());

      case REPLICATED:
        if (prj != null || partition() != null) return nodes(cctx, prj, partition());

        return cctx.affinityNode()
            ? Collections.singletonList(cctx.localNode())
            : Collections.singletonList(F.rand(nodes(cctx, null, partition())));

      case PARTITIONED:
        return nodes(cctx, prj, partition());

      default:
        throw new IllegalStateException("Unknown cache distribution mode: " + cacheMode);
    }
  }
  /**
   * Sends query request.
   *
   * @param fut Distributed future.
   * @param req Request.
   * @param nodes Nodes.
   * @throws IgniteCheckedException In case of error.
   */
  @SuppressWarnings("unchecked")
  private void sendRequest(
      final GridCacheDistributedQueryFuture<?, ?, ?> fut,
      final GridCacheQueryRequest req,
      Collection<ClusterNode> nodes)
      throws IgniteCheckedException {
    assert fut != null;
    assert req != null;
    assert nodes != null;

    final UUID locNodeId = cctx.localNodeId();

    ClusterNode locNode = null;

    Collection<ClusterNode> rmtNodes = null;

    for (ClusterNode n : nodes) {
      if (n.id().equals(locNodeId)) locNode = n;
      else {
        if (rmtNodes == null) rmtNodes = new ArrayList<>(nodes.size());

        rmtNodes.add(n);
      }
    }

    // Request should be sent to remote nodes before the query is processed on the local node.
    // For example, a remote reducer has a state, we should not serialize and then send
    // the reducer changed by the local node.
    if (!F.isEmpty(rmtNodes)) {
      cctx.io()
          .safeSend(
              rmtNodes,
              req,
              cctx.ioPolicy(),
              new P1<ClusterNode>() {
                @Override
                public boolean apply(ClusterNode node) {
                  fut.onNodeLeft(node.id());

                  return !fut.isDone();
                }
              });
    }

    if (locNode != null) {
      cctx.closures()
          .callLocalSafe(
              new Callable<Object>() {
                @Override
                public Object call() throws Exception {
                  req.beforeLocalExecution(cctx);

                  processQueryRequest(locNodeId, req);

                  return null;
                }
              });
    }
  }
  /**
   * @param rmtReducer Optional reducer.
   * @param rmtTransform Optional transformer.
   * @param args Arguments.
   * @return Future.
   */
  @SuppressWarnings("IfMayBeConditional")
  private <R> CacheQueryFuture<R> execute(
      @Nullable IgniteReducer<T, R> rmtReducer,
      @Nullable IgniteClosure<T, R> rmtTransform,
      @Nullable Object... args) {
    Collection<ClusterNode> nodes = nodes();

    cctx.checkSecurity(SecurityPermission.CACHE_READ);

    if (nodes.isEmpty())
      return new GridCacheQueryErrorFuture<>(
          cctx.kernalContext(), new ClusterGroupEmptyCheckedException());

    if (log.isDebugEnabled())
      log.debug("Executing query [query=" + this + ", nodes=" + nodes + ']');

    if (cctx.deploymentEnabled()) {
      try {
        cctx.deploy().registerClasses(filter, rmtReducer, rmtTransform);
        cctx.deploy().registerClasses(args);
      } catch (IgniteCheckedException e) {
        return new GridCacheQueryErrorFuture<>(cctx.kernalContext(), e);
      }
    }

    if (subjId == null) subjId = cctx.localNodeId();

    taskHash = cctx.kernalContext().job().currentTaskNameHash();

    final GridCacheQueryBean bean =
        new GridCacheQueryBean(
            this,
            (IgniteReducer<Object, Object>) rmtReducer,
            (IgniteClosure<Object, Object>) rmtTransform,
            args);

    final GridCacheQueryManager qryMgr = cctx.queries();

    boolean loc = nodes.size() == 1 && F.first(nodes).id().equals(cctx.localNodeId());

    if (type == SQL_FIELDS || type == SPI)
      return (CacheQueryFuture<R>)
          (loc ? qryMgr.queryFieldsLocal(bean) : qryMgr.queryFieldsDistributed(bean, nodes));
    else if (type == SCAN && part != null && nodes.size() > 1)
      return new CacheQueryFallbackFuture<>(nodes, bean, qryMgr);
    else
      return (CacheQueryFuture<R>)
          (loc ? qryMgr.queryLocal(bean) : qryMgr.queryDistributed(bean, nodes));
  }
  /**
   * Processes cache query request.
   *
   * @param sndId Sender node id.
   * @param req Query request.
   */
  @SuppressWarnings("unchecked")
  @Override
  void processQueryRequest(UUID sndId, GridCacheQueryRequest req) {
    if (req.cancel()) {
      cancelIds.add(new CancelMessageId(req.id(), sndId));

      if (req.fields()) removeFieldsQueryResult(sndId, req.id());
      else removeQueryResult(sndId, req.id());
    } else {
      if (!cancelIds.contains(new CancelMessageId(req.id(), sndId))) {
        if (!F.eq(req.cacheName(), cctx.name())) {
          GridCacheQueryResponse res =
              new GridCacheQueryResponse(
                  cctx.cacheId(),
                  req.id(),
                  new IgniteCheckedException(
                      "Received request for incorrect cache [expected="
                          + cctx.name()
                          + ", actual="
                          + req.cacheName()));

          sendQueryResponse(sndId, res, 0);
        } else {
          threads.put(req.id(), Thread.currentThread());

          try {
            GridCacheQueryInfo info = distributedQueryInfo(sndId, req);

            if (info == null) return;

            if (req.fields()) runFieldsQuery(info);
            else runQuery(info);
          } catch (Throwable e) {
            U.error(log(), "Failed to run query.", e);

            sendQueryResponse(
                sndId, new GridCacheQueryResponse(cctx.cacheId(), req.id(), e.getCause()), 0);

            if (e instanceof Error) throw (Error) e;
          } finally {
            threads.remove(req.id());
          }
        }
      }
    }
  }
  /** Clears values for this partition. */
  private void clearAll() {
    GridCacheVersion clearVer = cctx.versions().next();

    boolean swap = cctx.isSwapOrOffheapEnabled();

    boolean rec = cctx.events().isRecordable(EVT_CACHE_REBALANCE_OBJECT_UNLOADED);

    Iterator<GridDhtCacheEntry> it = map.values().iterator();

    GridCloseableIterator<Map.Entry<byte[], GridCacheSwapEntry>> swapIt = null;

    if (swap
        && GridQueryProcessor.isEnabled(cctx.config())) { // Indexing needs to unswap cache values.
      Iterator<GridDhtCacheEntry> unswapIt = null;

      try {
        swapIt = cctx.swap().iterator(id);
        unswapIt = unswapIterator(swapIt);
      } catch (Exception e) {
        U.error(log, "Failed to clear swap for evicted partition: " + this, e);
      }

      if (unswapIt != null) it = F.concat(it, unswapIt);
    }

    try {
      while (it.hasNext()) {
        GridDhtCacheEntry cached = it.next();

        try {
          if (cached.clearInternal(clearVer, swap)) {
            map.remove(cached.key(), cached);

            if (!cached.isInternal()) {
              mapPubSize.decrement();

              if (rec)
                cctx.events()
                    .addEvent(
                        cached.partition(),
                        cached.key(),
                        cctx.localNodeId(),
                        (IgniteUuid) null,
                        null,
                        EVT_CACHE_REBALANCE_OBJECT_UNLOADED,
                        null,
                        false,
                        cached.rawGet(),
                        cached.hasValue(),
                        null,
                        null,
                        null);
            }
          }
        } catch (IgniteCheckedException e) {
          U.error(log, "Failed to clear cache entry for evicted partition: " + cached, e);
        }
      }
    } finally {
      U.close(swapIt, log);
    }
  }