public MetaData build() {
      // TODO: We should move these datastructures to IndexNameExpressionResolver, this will give
      // the following benefits:
      // 1) The datastructures will only be rebuilded when needed. Now during serializing we rebuild
      // these datastructures
      //    while these datastructures aren't even used.
      // 2) The aliasAndIndexLookup can be updated instead of rebuilding it all the time.

      // build all concrete indices arrays:
      // TODO: I think we can remove these arrays. it isn't worth the effort, for operations on all
      // indices.
      // When doing an operation across all indices, most of the time is spent on actually going to
      // all shards and
      // do the required operations, the bottleneck isn't resolving expressions into concrete
      // indices.
      List<String> allIndicesLst = new ArrayList<>();
      for (ObjectCursor<IndexMetaData> cursor : indices.values()) {
        allIndicesLst.add(cursor.value.getIndex().getName());
      }
      String[] allIndices = allIndicesLst.toArray(new String[allIndicesLst.size()]);

      List<String> allOpenIndicesLst = new ArrayList<>();
      List<String> allClosedIndicesLst = new ArrayList<>();
      for (ObjectCursor<IndexMetaData> cursor : indices.values()) {
        IndexMetaData indexMetaData = cursor.value;
        if (indexMetaData.getState() == IndexMetaData.State.OPEN) {
          allOpenIndicesLst.add(indexMetaData.getIndex().getName());
        } else if (indexMetaData.getState() == IndexMetaData.State.CLOSE) {
          allClosedIndicesLst.add(indexMetaData.getIndex().getName());
        }
      }
      String[] allOpenIndices = allOpenIndicesLst.toArray(new String[allOpenIndicesLst.size()]);
      String[] allClosedIndices =
          allClosedIndicesLst.toArray(new String[allClosedIndicesLst.size()]);

      // build all indices map
      SortedMap<String, AliasOrIndex> aliasAndIndexLookup = new TreeMap<>();
      for (ObjectCursor<IndexMetaData> cursor : indices.values()) {
        IndexMetaData indexMetaData = cursor.value;
        aliasAndIndexLookup.put(
            indexMetaData.getIndex().getName(), new AliasOrIndex.Index(indexMetaData));

        for (ObjectObjectCursor<String, AliasMetaData> aliasCursor : indexMetaData.getAliases()) {
          AliasMetaData aliasMetaData = aliasCursor.value;
          AliasOrIndex aliasOrIndex = aliasAndIndexLookup.get(aliasMetaData.getAlias());
          if (aliasOrIndex == null) {
            aliasOrIndex = new AliasOrIndex.Alias(aliasMetaData, indexMetaData);
            aliasAndIndexLookup.put(aliasMetaData.getAlias(), aliasOrIndex);
          } else if (aliasOrIndex instanceof AliasOrIndex.Alias) {
            AliasOrIndex.Alias alias = (AliasOrIndex.Alias) aliasOrIndex;
            alias.addIndex(indexMetaData);
          } else if (aliasOrIndex instanceof AliasOrIndex.Index) {
            AliasOrIndex.Index index = (AliasOrIndex.Index) aliasOrIndex;
            throw new IllegalStateException(
                "index and alias names need to be unique, but alias ["
                    + aliasMetaData.getAlias()
                    + "] and index "
                    + index.getIndex().getIndex()
                    + " have the same name");
          } else {
            throw new IllegalStateException(
                "unexpected alias [" + aliasMetaData.getAlias() + "][" + aliasOrIndex + "]");
          }
        }
      }
      aliasAndIndexLookup = Collections.unmodifiableSortedMap(aliasAndIndexLookup);
      return new MetaData(
          clusterUUID,
          version,
          transientSettings,
          persistentSettings,
          indices.build(),
          templates.build(),
          customs.build(),
          allIndices,
          allOpenIndices,
          allClosedIndices,
          aliasAndIndexLookup);
    }
    public IndexMetaData build() {
      ImmutableOpenMap.Builder<String, AliasMetaData> tmpAliases = aliases;
      Settings tmpSettings = settings;

      // update default mapping on the MappingMetaData
      if (mappings.containsKey(MapperService.DEFAULT_MAPPING)) {
        MappingMetaData defaultMapping = mappings.get(MapperService.DEFAULT_MAPPING);
        for (ObjectCursor<MappingMetaData> cursor : mappings.values()) {
          cursor.value.updateDefaultMapping(defaultMapping);
        }
      }

      Integer maybeNumberOfShards = settings.getAsInt(SETTING_NUMBER_OF_SHARDS, null);
      if (maybeNumberOfShards == null) {
        throw new IllegalArgumentException("must specify numberOfShards for index [" + index + "]");
      }
      int numberOfShards = maybeNumberOfShards;
      if (numberOfShards <= 0) {
        throw new IllegalArgumentException(
            "must specify positive number of shards for index [" + index + "]");
      }

      Integer maybeNumberOfReplicas = settings.getAsInt(SETTING_NUMBER_OF_REPLICAS, null);
      if (maybeNumberOfReplicas == null) {
        throw new IllegalArgumentException(
            "must specify numberOfReplicas for index [" + index + "]");
      }
      int numberOfReplicas = maybeNumberOfReplicas;
      if (numberOfReplicas < 0) {
        throw new IllegalArgumentException(
            "must specify non-negative number of shards for index [" + index + "]");
      }

      // fill missing slots in activeAllocationIds with empty set if needed and make all entries
      // immutable
      ImmutableOpenIntMap.Builder<Set<String>> filledActiveAllocationIds =
          ImmutableOpenIntMap.builder();
      for (int i = 0; i < numberOfShards; i++) {
        if (activeAllocationIds.containsKey(i)) {
          filledActiveAllocationIds.put(
              i, Collections.unmodifiableSet(new HashSet<>(activeAllocationIds.get(i))));
        } else {
          filledActiveAllocationIds.put(i, Collections.emptySet());
        }
      }
      final Map<String, String> requireMap =
          INDEX_ROUTING_REQUIRE_GROUP_SETTING.get(settings).getAsMap();
      final DiscoveryNodeFilters requireFilters;
      if (requireMap.isEmpty()) {
        requireFilters = null;
      } else {
        requireFilters = DiscoveryNodeFilters.buildFromKeyValue(AND, requireMap);
      }
      Map<String, String> includeMap = INDEX_ROUTING_INCLUDE_GROUP_SETTING.get(settings).getAsMap();
      final DiscoveryNodeFilters includeFilters;
      if (includeMap.isEmpty()) {
        includeFilters = null;
      } else {
        includeFilters = DiscoveryNodeFilters.buildFromKeyValue(OR, includeMap);
      }
      Map<String, String> excludeMap = INDEX_ROUTING_EXCLUDE_GROUP_SETTING.get(settings).getAsMap();
      final DiscoveryNodeFilters excludeFilters;
      if (excludeMap.isEmpty()) {
        excludeFilters = null;
      } else {
        excludeFilters = DiscoveryNodeFilters.buildFromKeyValue(OR, excludeMap);
      }
      Version indexCreatedVersion = Version.indexCreated(settings);
      Version indexUpgradedVersion =
          settings.getAsVersion(IndexMetaData.SETTING_VERSION_UPGRADED, indexCreatedVersion);
      String stringLuceneVersion = settings.get(SETTING_VERSION_MINIMUM_COMPATIBLE);
      final org.apache.lucene.util.Version minimumCompatibleLuceneVersion;
      if (stringLuceneVersion != null) {
        try {
          minimumCompatibleLuceneVersion =
              org.apache.lucene.util.Version.parse(stringLuceneVersion);
        } catch (ParseException ex) {
          throw new IllegalStateException(
              "Cannot parse lucene version ["
                  + stringLuceneVersion
                  + "] in the ["
                  + SETTING_VERSION_MINIMUM_COMPATIBLE
                  + "] setting",
              ex);
        }
      } else {
        minimumCompatibleLuceneVersion = null;
      }

      final String uuid = settings.get(SETTING_INDEX_UUID, INDEX_UUID_NA_VALUE);
      return new IndexMetaData(
          new Index(index, uuid),
          version,
          state,
          numberOfShards,
          numberOfReplicas,
          tmpSettings,
          mappings.build(),
          tmpAliases.build(),
          customs.build(),
          filledActiveAllocationIds.build(),
          requireFilters,
          includeFilters,
          excludeFilters,
          indexCreatedVersion,
          indexUpgradedVersion,
          minimumCompatibleLuceneVersion);
    }