Use HashMap for IndexMetadata.inSyncAllocationIds (#86403)

The in sync allocation ids is a mapping from shard to the set of ids
currently being processed. When being built, the metadata uses a sparse
map, only filling a value for a shard as they are put into the builder.
When the final metadata is built, the map is made dense.

This commit converts to using a HashMap instead of ImmutableOpenIntMap.
The boxed keys should not cause allocations, as long as number of shards
is lower than 128. Long term the map itself should become an array, as
we know the number of shards (much like the dense primaryTerms array
here). However, that change will be a little trickier to make, since we
will need to be backward compatible with how diffs are built, currently
using Map differences.

relates #86239

Author: rjernst

server/src/main/java/org/elasticsearch/cluster/metadata/IndexMetadata.java

@@ -22,7 +22,6 @@
 import org.elasticsearch.cluster.routing.allocation.IndexMetadataUpdater;
 import org.elasticsearch.cluster.routing.allocation.decider.DiskThresholdDecider;
 import org.elasticsearch.cluster.routing.allocation.decider.ShardsLimitAllocationDecider;
-import org.elasticsearch.common.collect.ImmutableOpenIntMap;
 import org.elasticsearch.common.collect.ImmutableOpenMap;
 import org.elasticsearch.common.collect.MapBuilder;
 import org.elasticsearch.common.compress.CompressedXContent;
@@ -58,6 +57,7 @@
 import java.util.Arrays;
 import java.util.Collections;
 import java.util.EnumSet;
+import java.util.HashMap;
 import java.util.HashSet;
 import java.util.Iterator;
 import java.util.List;
@@ -516,7 +516,7 @@ public Iterator<Setting<?>> settings() {
 
     private final ImmutableOpenMap<String, DiffableStringMap> customData;
 
-    private final ImmutableOpenIntMap<Set<String>> inSyncAllocationIds;
+    private final Map<Integer, Set<String>> inSyncAllocationIds;
 
     private final transient int totalNumberOfShards;
 
@@ -571,7 +571,7 @@ private IndexMetadata(
         final MappingMetadata mapping,
         final ImmutableOpenMap<String, AliasMetadata> aliases,
         final ImmutableOpenMap<String, DiffableStringMap> customData,
-        final ImmutableOpenIntMap<Set<String>> inSyncAllocationIds,
+        final Map<Integer, Set<String>> inSyncAllocationIds,
         final DiscoveryNodeFilters requireFilters,
         final DiscoveryNodeFilters initialRecoveryFilters,
         final DiscoveryNodeFilters includeFilters,
@@ -889,7 +889,7 @@ public Map<String, String> getCustomData(final String key) {
         return this.customData.get(key);
     }
 
-    public ImmutableOpenIntMap<Set<String>> getInSyncAllocationIds() {
+    public Map<Integer, Set<String>> getInSyncAllocationIds() {
         return inSyncAllocationIds;
     }
 
@@ -1031,7 +1031,7 @@ private static class IndexMetadataDiff implements Diff<IndexMetadata> {
         private final Diff<ImmutableOpenMap<String, MappingMetadata>> mappings;
         private final Diff<ImmutableOpenMap<String, AliasMetadata>> aliases;
         private final Diff<ImmutableOpenMap<String, DiffableStringMap>> customData;
-        private final Diff<ImmutableOpenIntMap<Set<String>>> inSyncAllocationIds;
+        private final Diff<Map<Integer, Set<String>>> inSyncAllocationIds;
         private final Diff<ImmutableOpenMap<String, RolloverInfo>> rolloverInfos;
         private final boolean isSystem;
         private final IndexLongFieldRange timestampRange;
@@ -1095,7 +1095,7 @@ private static class IndexMetadataDiff implements Diff<IndexMetadata> {
             mappings = DiffableUtils.readImmutableOpenMapDiff(in, DiffableUtils.getStringKeySerializer(), MAPPING_DIFF_VALUE_READER);
             aliases = DiffableUtils.readImmutableOpenMapDiff(in, DiffableUtils.getStringKeySerializer(), ALIAS_METADATA_DIFF_VALUE_READER);
             customData = DiffableUtils.readImmutableOpenMapDiff(in, DiffableUtils.getStringKeySerializer(), CUSTOM_DIFF_VALUE_READER);
-            inSyncAllocationIds = DiffableUtils.readImmutableOpenIntMapDiff(
+            inSyncAllocationIds = DiffableUtils.readJdkMapDiff(
                 in,
                 DiffableUtils.getVIntKeySerializer(),
                 DiffableUtils.StringSetValueSerializer.getInstance()
@@ -1153,7 +1153,7 @@ public IndexMetadata apply(IndexMetadata part) {
             ).get(MapperService.SINGLE_MAPPING_NAME);
             builder.aliases.putAllFromMap(aliases.apply(part.aliases));
             builder.customMetadata.putAllFromMap(customData.apply(part.customData));
-            builder.inSyncAllocationIds.putAll((Map<Integer, Set<String>>) inSyncAllocationIds.apply(part.inSyncAllocationIds));
+            builder.inSyncAllocationIds.putAll(inSyncAllocationIds.apply(part.inSyncAllocationIds));
             builder.rolloverInfos.putAllFromMap(rolloverInfos.apply(part.rolloverInfos));
             builder.system(isSystem);
             builder.timestampRange(timestampRange);
@@ -1309,7 +1309,7 @@ public static class Builder {
         private MappingMetadata mapping;
         private final ImmutableOpenMap.Builder<String, AliasMetadata> aliases;
         private final ImmutableOpenMap.Builder<String, DiffableStringMap> customMetadata;
-        private final ImmutableOpenIntMap.Builder<Set<String>> inSyncAllocationIds;
+        private final Map<Integer, Set<String>> inSyncAllocationIds;
         private final ImmutableOpenMap.Builder<String, RolloverInfo> rolloverInfos;
         private Integer routingNumShards;
         private boolean isSystem;
@@ -1320,7 +1320,7 @@ public Builder(String index) {
             this.index = index;
             this.aliases = ImmutableOpenMap.builder();
             this.customMetadata = ImmutableOpenMap.builder();
-            this.inSyncAllocationIds = ImmutableOpenIntMap.builder();
+            this.inSyncAllocationIds = new HashMap<>();
             this.rolloverInfos = ImmutableOpenMap.builder();
             this.isSystem = false;
         }
@@ -1338,7 +1338,7 @@ public Builder(IndexMetadata indexMetadata) {
             this.aliases = ImmutableOpenMap.builder(indexMetadata.aliases);
             this.customMetadata = ImmutableOpenMap.builder(indexMetadata.customData);
             this.routingNumShards = indexMetadata.routingNumShards;
-            this.inSyncAllocationIds = ImmutableOpenIntMap.builder(indexMetadata.inSyncAllocationIds);
+            this.inSyncAllocationIds = new HashMap<>(indexMetadata.inSyncAllocationIds);
             this.rolloverInfos = ImmutableOpenMap.builder(indexMetadata.rolloverInfos);
             this.isSystem = indexMetadata.isSystem;
             this.timestampRange = indexMetadata.timestampRange;
@@ -1466,7 +1466,7 @@ public Set<String> getInSyncAllocationIds(int shardId) {
         }
 
         public Builder putInSyncAllocationIds(int shardId, Set<String> allocationIds) {
-            inSyncAllocationIds.put(shardId, new HashSet<>(allocationIds));
+            inSyncAllocationIds.put(shardId, Set.copyOf(allocationIds));
             return this;
         }
 
@@ -1595,13 +1595,11 @@ public IndexMetadata build() {
             }
 
             // fill missing slots in inSyncAllocationIds with empty set if needed and make all entries immutable
-            ImmutableOpenIntMap.Builder<Set<String>> filledInSyncAllocationIds = ImmutableOpenIntMap.builder();
+            @SuppressWarnings({ "unchecked", "rawtypes" })
+            Map.Entry<Integer, Set<String>> denseInSyncAllocationIds[] = new Map.Entry[numberOfShards];
             for (int i = 0; i < numberOfShards; i++) {
-                if (inSyncAllocationIds.containsKey(i)) {
-                    filledInSyncAllocationIds.put(i, Set.copyOf(inSyncAllocationIds.get(i)));
-                } else {
-                    filledInSyncAllocationIds.put(i, Collections.emptySet());
-                }
+                Set<String> allocIds = inSyncAllocationIds.getOrDefault(i, Set.of());
+                denseInSyncAllocationIds[i] = Map.entry(i, allocIds);
             }
             var requireMap = INDEX_ROUTING_REQUIRE_GROUP_SETTING.getAsMap(settings);
             final DiscoveryNodeFilters requireFilters;
@@ -1697,7 +1695,7 @@ public IndexMetadata build() {
                 mapping,
                 aliases.build(),
                 newCustomMetadata,
-                filledInSyncAllocationIds.build(),
+                Map.ofEntries(denseInSyncAllocationIds),
                 requireFilters,
                 initialRecoveryFilters,
                 includeFilters,
@@ -2019,7 +2017,7 @@ public static IndexMetadata legacyFromXContent(XContentParser parser) throws IOE
                                         allocationIds.add(parser.text());
                                     }
                                 }
-                                builder.putInSyncAllocationIds(Integer.valueOf(shardId), allocationIds);
+                                builder.putInSyncAllocationIds(Integer.parseInt(shardId), allocationIds);
                             } else {
                                 throw new IllegalArgumentException("Unexpected token: " + token);
                             }