Introduce a Few Settings Singleton Instances (#78897)

This is mostly motivated by the ILM steps changes, that showed up as hot in
profiling since instantiating a `Settings` instance turns out to be somewhat expensive.
Also cleans up a couple of other spots and some duplication as well.

client/rest-high-level/src/main/java/org/elasticsearch/client/indices/CreateIndexRequest.java

@@ -36,8 +36,6 @@
 import java.util.Objects;
 import java.util.Set;
 
-import static org.elasticsearch.common.settings.Settings.Builder.EMPTY_SETTINGS;
-
 /**
  * A request to create an index.
  */
@@ -47,7 +45,7 @@ public class CreateIndexRequest extends TimedRequest implements Validatable, ToX
     static final ParseField ALIASES = new ParseField("aliases");
 
     private final String index;
-    private Settings settings = EMPTY_SETTINGS;
+    private Settings settings = Settings.EMPTY;
 
     private BytesReference mappings;
     private XContentType mappingsXContentType;

client/rest-high-level/src/main/java/org/elasticsearch/client/indices/IndexTemplateMetadata.java

@@ -178,7 +178,7 @@ public static class Builder {
 
         private List<String> indexPatterns;
 
-        private Settings settings = Settings.Builder.EMPTY_SETTINGS;
+        private Settings settings = Settings.EMPTY;
 
         private MappingMetadata mappings;
 

client/rest-high-level/src/main/java/org/elasticsearch/client/indices/PutIndexTemplateRequest.java

@@ -36,8 +36,6 @@
 import java.util.Set;
 import java.util.stream.Collectors;
 
-import static org.elasticsearch.common.settings.Settings.Builder.EMPTY_SETTINGS;
-
 /**
  * A request to create an index template.
  */
@@ -53,7 +51,7 @@ public class PutIndexTemplateRequest extends TimedRequest implements ToXContentF
 
     private boolean create;
 
-    private Settings settings = EMPTY_SETTINGS;
+    private Settings settings = Settings.EMPTY;
 
     private BytesReference mappings = null;
 

server/src/internalClusterTest/java/org/elasticsearch/recovery/SimpleRecoveryIT.java

@@ -29,7 +29,7 @@ public Settings indexSettings() {
     }
 
     protected Settings recoverySettings() {
-        return Settings.Builder.EMPTY_SETTINGS;
+        return Settings.EMPTY;
     }
 
     @Override

server/src/main/java/org/elasticsearch/action/admin/cluster/repositories/put/PutRepositoryRequest.java

@@ -21,7 +21,6 @@
 import java.util.Map;
 
 import static org.elasticsearch.action.ValidateActions.addValidationError;
-import static org.elasticsearch.common.settings.Settings.Builder.EMPTY_SETTINGS;
 import static org.elasticsearch.common.settings.Settings.readSettingsFromStream;
 import static org.elasticsearch.common.settings.Settings.writeSettingsToStream;
 
@@ -39,7 +38,7 @@ public class PutRepositoryRequest extends AcknowledgedRequest<PutRepositoryReque
 
     private boolean verify = true;
 
-    private Settings settings = EMPTY_SETTINGS;
+    private Settings settings = Settings.EMPTY;
 
     public PutRepositoryRequest(StreamInput in) throws IOException {
         super(in);

server/src/main/java/org/elasticsearch/action/admin/cluster/settings/ClusterUpdateSettingsRequest.java

@@ -26,7 +26,6 @@
 import static org.elasticsearch.action.ValidateActions.addValidationError;
 import static org.elasticsearch.common.settings.Settings.readSettingsFromStream;
 import static org.elasticsearch.common.settings.Settings.writeSettingsToStream;
-import static org.elasticsearch.common.settings.Settings.Builder.EMPTY_SETTINGS;
 
 /**
  * Request for an update cluster settings action
@@ -44,8 +43,8 @@ public class ClusterUpdateSettingsRequest extends AcknowledgedRequest<ClusterUpd
         PARSER.declareObject((r, t) -> r.transientSettings = t, (p, c) -> Settings.fromXContent(p), TRANSIENT);
     }
 
-    private Settings transientSettings = EMPTY_SETTINGS;
-    private Settings persistentSettings = EMPTY_SETTINGS;
+    private Settings transientSettings = Settings.EMPTY;
+    private Settings persistentSettings = Settings.EMPTY;
 
     public ClusterUpdateSettingsRequest(StreamInput in) throws IOException {
         super(in);

server/src/main/java/org/elasticsearch/action/admin/cluster/snapshots/restore/RestoreSnapshotRequest.java

@@ -28,7 +28,6 @@
 import java.util.Objects;
 
 import static org.elasticsearch.action.ValidateActions.addValidationError;
-import static org.elasticsearch.common.settings.Settings.Builder.EMPTY_SETTINGS;
 import static org.elasticsearch.common.settings.Settings.readSettingsFromStream;
 import static org.elasticsearch.common.settings.Settings.writeSettingsToStream;
 import static org.elasticsearch.common.xcontent.support.XContentMapValues.nodeBooleanValue;
@@ -49,7 +48,7 @@ public class RestoreSnapshotRequest extends MasterNodeRequest<RestoreSnapshotReq
     private boolean includeGlobalState = false;
     private boolean partial = false;
     private boolean includeAliases = true;
-    private Settings indexSettings = EMPTY_SETTINGS;
+    private Settings indexSettings = Settings.EMPTY;
     private String[] ignoreIndexSettings = Strings.EMPTY_ARRAY;
 
     // This field does not get serialised (except toString for debugging purpose) because it is always set locally by authz

server/src/main/java/org/elasticsearch/action/admin/indices/create/CreateIndexClusterStateUpdateRequest.java

@@ -36,7 +36,7 @@ public class CreateIndexClusterStateUpdateRequest extends ClusterStateUpdateRequ
     private boolean copySettings;
     private SystemDataStreamDescriptor systemDataStreamDescriptor;
 
-    private Settings settings = Settings.Builder.EMPTY_SETTINGS;
+    private Settings settings = Settings.EMPTY;
 
     private String mappings = "{}";
 

server/src/main/java/org/elasticsearch/action/admin/indices/create/CreateIndexRequest.java

@@ -42,7 +42,6 @@
 import java.util.Set;
 
 import static org.elasticsearch.action.ValidateActions.addValidationError;
-import static org.elasticsearch.common.settings.Settings.Builder.EMPTY_SETTINGS;
 import static org.elasticsearch.common.settings.Settings.readSettingsFromStream;
 import static org.elasticsearch.common.settings.Settings.writeSettingsToStream;
 
@@ -65,7 +64,7 @@ public class CreateIndexRequest extends AcknowledgedRequest<CreateIndexRequest>
 
     private String index;
 
-    private Settings settings = EMPTY_SETTINGS;
+    private Settings settings = Settings.EMPTY;
 
     private String mappings = "{}";
 
@@ -116,7 +115,7 @@ public CreateIndexRequest() {
      * @param index the name of the index
      */
     public CreateIndexRequest(String index) {
-        this(index, EMPTY_SETTINGS);
+        this(index, Settings.EMPTY);
     }
 
     /**

server/src/main/java/org/elasticsearch/action/admin/indices/rollover/MetadataRolloverService.java

@@ -53,6 +53,8 @@ public class MetadataRolloverService {
     private static final Pattern INDEX_NAME_PATTERN = Pattern.compile("^.*-\\d+$");
     private static final List<IndexAbstraction.Type> VALID_ROLLOVER_TARGETS = List.of(ALIAS, DATA_STREAM);
 
+    public static final Settings HIDDEN_INDEX_SETTINGS = Settings.builder().put(IndexMetadata.SETTING_INDEX_HIDDEN, true).build();
+
     private final ThreadPool threadPool;
     private final MetadataCreateIndexService createIndexService;
     private final MetadataIndexAliasesService indexAliasesService;
@@ -272,7 +274,7 @@ static CreateIndexClusterStateUpdateRequest prepareDataStreamCreateIndexRequest(
                                                                                     final String targetIndexName,
                                                                                     CreateIndexRequest createIndexRequest,
                                                                                     final SystemDataStreamDescriptor descriptor) {
-        Settings settings = descriptor != null ? Settings.EMPTY : Settings.builder().put("index.hidden", true).build();
+        Settings settings = descriptor != null ? Settings.EMPTY : HIDDEN_INDEX_SETTINGS;
         return prepareCreateIndexRequest(targetIndexName, targetIndexName, "rollover_data_stream", createIndexRequest, settings)
             .dataStreamName(dataStreamName)
             .systemDataStreamDescriptor(descriptor);

server/src/main/java/org/elasticsearch/action/admin/indices/settings/put/UpdateSettingsRequest.java

@@ -31,7 +31,6 @@
 import static org.elasticsearch.action.ValidateActions.addValidationError;
 import static org.elasticsearch.common.settings.Settings.readSettingsFromStream;
 import static org.elasticsearch.common.settings.Settings.writeSettingsToStream;
-import static org.elasticsearch.common.settings.Settings.Builder.EMPTY_SETTINGS;
 
 /**
  * Request for an update index settings action
@@ -43,7 +42,7 @@ public class UpdateSettingsRequest extends AcknowledgedRequest<UpdateSettingsReq
 
     private String[] indices;
     private IndicesOptions indicesOptions = DEFAULT_INDICES_OPTIONS;
-    private Settings settings = EMPTY_SETTINGS;
+    private Settings settings = Settings.EMPTY;
     private boolean preserveExisting = false;
     private String origin = "";
 

server/src/main/java/org/elasticsearch/action/admin/indices/template/put/PutIndexTemplateRequest.java

@@ -43,7 +43,6 @@
 import java.util.stream.Collectors;
 
 import static org.elasticsearch.action.ValidateActions.addValidationError;
-import static org.elasticsearch.common.settings.Settings.Builder.EMPTY_SETTINGS;
 import static org.elasticsearch.common.settings.Settings.readSettingsFromStream;
 import static org.elasticsearch.common.settings.Settings.writeSettingsToStream;
 
@@ -62,7 +61,7 @@ public class PutIndexTemplateRequest extends MasterNodeRequest<PutIndexTemplateR
 
     private boolean create;
 
-    private Settings settings = EMPTY_SETTINGS;
+    private Settings settings = Settings.EMPTY;
 
     @Nullable
     private String mappings;

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

@@ -992,7 +992,7 @@ public static class Builder {
         private long settingsVersion = 1;
         private long aliasesVersion = 1;
         private long[] primaryTerms = null;
-        private Settings settings = Settings.Builder.EMPTY_SETTINGS;
+        private Settings settings = Settings.EMPTY;
         private final ImmutableOpenMap.Builder<String, MappingMetadata> mappings;
         private final ImmutableOpenMap.Builder<String, AliasMetadata> aliases;
         private final ImmutableOpenMap.Builder<String, DiffableStringMap> customMetadata;

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

@@ -245,7 +245,7 @@ public static class Builder {
 
         private List<String> indexPatterns;
 
-        private Settings settings = Settings.Builder.EMPTY_SETTINGS;
+        private Settings settings = Settings.EMPTY;
 
         private final ImmutableOpenMap.Builder<String, CompressedXContent> mappings;
 

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

@@ -1029,8 +1029,8 @@ public static class Builder {
         private long version;
 
         private CoordinationMetadata coordinationMetadata = CoordinationMetadata.EMPTY_METADATA;
-        private Settings transientSettings = Settings.Builder.EMPTY_SETTINGS;
-        private Settings persistentSettings = Settings.Builder.EMPTY_SETTINGS;
+        private Settings transientSettings = Settings.EMPTY;
+        private Settings persistentSettings = Settings.EMPTY;
         private DiffableStringMap hashesOfConsistentSettings = DiffableStringMap.EMPTY;
 
         private final ImmutableOpenMap.Builder<String, IndexMetadata> indices;

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

@@ -13,6 +13,7 @@
 import org.elasticsearch.ResourceAlreadyExistsException;
 import org.elasticsearch.action.ActionListener;
 import org.elasticsearch.action.admin.indices.create.CreateIndexClusterStateUpdateRequest;
+import org.elasticsearch.action.admin.indices.rollover.MetadataRolloverService;
 import org.elasticsearch.action.support.ActiveShardCount;
 import org.elasticsearch.action.support.ActiveShardsObserver;
 import org.elasticsearch.action.support.master.AcknowledgedResponse;
@@ -22,7 +23,6 @@
 import org.elasticsearch.cluster.service.ClusterService;
 import org.elasticsearch.common.Priority;
 import org.elasticsearch.common.Strings;
-import org.elasticsearch.common.settings.Settings;
 import org.elasticsearch.core.TimeValue;
 import org.elasticsearch.index.Index;
 import org.elasticsearch.index.mapper.DataStreamTimestampFieldMapper;
@@ -195,7 +195,7 @@ static ClusterState createDataStream(MetadataCreateIndexService metadataCreateIn
                     .systemDataStreamDescriptor(systemDataStreamDescriptor);
 
             if (isSystem == false) {
-                createIndexRequest.settings(Settings.builder().put("index.hidden", true).build());
+                createIndexRequest.settings(MetadataRolloverService.HIDDEN_INDEX_SETTINGS);
             }
 
             try {

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

@@ -1424,7 +1424,7 @@ public static class PutRequest {
         int order;
         Integer version;
         List<String> indexPatterns;
-        Settings settings = Settings.Builder.EMPTY_SETTINGS;
+        Settings settings = Settings.EMPTY;
         String mappings = null;
         List<Alias> aliases = new ArrayList<>();
 

server/src/main/java/org/elasticsearch/cluster/routing/allocation/DataTier.java

@@ -21,12 +21,12 @@
 import org.elasticsearch.snapshots.SearchableSnapshotsSettings;
 
 import java.util.Collection;
+import java.util.HashMap;
 import java.util.Iterator;
 import java.util.List;
 import java.util.Map;
 import java.util.Set;
 import java.util.function.Function;
-import java.util.stream.Collectors;
 
 /**
  * The {@code DataTier} class encapsulates the formalization of the "content",
@@ -46,6 +46,12 @@ public class DataTier {
 
     public static final String TIER_PREFERENCE = "index.routing.allocation.include._tier_preference";
 
+    private static final Settings DATA_CONTENT_TIER_PREFERENCE_SETTINGS = Settings.builder().put(TIER_PREFERENCE, DATA_CONTENT).build();
+
+    private static final Settings DATA_HOT_TIER_PREFERENCE_SETTINGS = Settings.builder().put(TIER_PREFERENCE, DATA_HOT).build();
+
+    private static final Settings NULL_TIER_PREFERENCE_SETTINGS = Settings.builder().putNull(TIER_PREFERENCE).build();
+
     public static final Setting<String> TIER_PREFERENCE_SETTING = new Setting<>(
         new Setting.SimpleKey(TIER_PREFERENCE),
         DataTierSettingValidator::getDefaultTierPreference,
@@ -66,6 +72,24 @@ public class DataTier {
     // Represents an ordered list of data tiers from frozen to hot (or slow to fast)
     private static final List<String> ORDERED_FROZEN_TO_HOT_TIERS = List.of(DATA_FROZEN, DATA_COLD, DATA_WARM, DATA_HOT);
 
+    private static final Map<String, String> PREFERENCE_TIER_CONFIGURATIONS;
+
+    private static final Map<String, Settings> PREFERENCE_TIER_CONFIGURATION_SETTINGS;
+
+    static {
+        final Map<String, String> tmp = new HashMap<>();
+        final Map<String, Settings> tmpSettings = new HashMap<>();
+        for (int i = 0, ordered_frozen_to_hot_tiersSize = ORDERED_FROZEN_TO_HOT_TIERS.size(); i < ordered_frozen_to_hot_tiersSize; i++) {
+            String tier = ORDERED_FROZEN_TO_HOT_TIERS.get(i);
+            final String prefTierString =
+                String.join(",", ORDERED_FROZEN_TO_HOT_TIERS.subList(i, ORDERED_FROZEN_TO_HOT_TIERS.size())).intern();
+            tmp.put(tier, prefTierString);
+            tmpSettings.put(tier, Settings.builder().put(DataTier.TIER_PREFERENCE, prefTierString).build());
+        }
+        PREFERENCE_TIER_CONFIGURATIONS = Map.copyOf(tmp);
+        PREFERENCE_TIER_CONFIGURATION_SETTINGS = Map.copyOf(tmpSettings);
+    }
+
     /**
      * Returns true if the given tier name is a valid tier
      */
@@ -79,11 +103,19 @@ public static boolean validTierName(String tierName) {
      * This is usually used in conjunction with {@link #TIER_PREFERENCE_SETTING}.
      */
     public static String getPreferredTiersConfiguration(String targetTier) {
-        int indexOfTargetTier = ORDERED_FROZEN_TO_HOT_TIERS.indexOf(targetTier);
-        if (indexOfTargetTier == -1) {
+        final String res = PREFERENCE_TIER_CONFIGURATIONS.get(targetTier);
+        if (res == null) {
+            throw new IllegalArgumentException("invalid data tier [" + targetTier + "]");
+        }
+        return res;
+    }
+
+    public static Settings getPreferredTiersConfigurationSettings(String targetTier) {
+        final Settings res = PREFERENCE_TIER_CONFIGURATION_SETTINGS.get(targetTier);
+        if (res == null) {
             throw new IllegalArgumentException("invalid data tier [" + targetTier + "]");
         }
-        return ORDERED_FROZEN_TO_HOT_TIERS.stream().skip(indexOfTargetTier).collect(Collectors.joining(","));
+        return res;
     }
 
     /**
@@ -155,7 +187,7 @@ public Settings getAdditionalIndexSettings(String indexName, boolean isDataStrea
             Set<String> settings = indexSettings.keySet();
             if (settings.contains(TIER_PREFERENCE)) {
                 // just a marker -- this null value will be removed or overridden by the template/request settings
-                return Settings.builder().putNull(TIER_PREFERENCE).build();
+                return NULL_TIER_PREFERENCE_SETTINGS;
             } else if (settings.stream().anyMatch(s -> s.startsWith(IndexMetadata.INDEX_ROUTING_REQUIRE_GROUP_PREFIX + ".")) ||
                 settings.stream().anyMatch(s -> s.startsWith(IndexMetadata.INDEX_ROUTING_EXCLUDE_GROUP_PREFIX + ".")) ||
                 settings.stream().anyMatch(s -> s.startsWith(IndexMetadata.INDEX_ROUTING_INCLUDE_GROUP_PREFIX + "."))) {
@@ -167,9 +199,9 @@ public Settings getAdditionalIndexSettings(String indexName, boolean isDataStrea
                 // tier if the index is part of a data stream, the "content"
                 // tier if it is not.
                 if (isDataStreamIndex) {
-                    return Settings.builder().put(TIER_PREFERENCE, DATA_HOT).build();
+                    return DATA_HOT_TIER_PREFERENCE_SETTINGS;
                 } else {
-                    return Settings.builder().put(TIER_PREFERENCE, DATA_CONTENT).build();
+                    return DATA_CONTENT_TIER_PREFERENCE_SETTINGS;
                 }
             }
         }

server/src/main/java/org/elasticsearch/cluster/routing/allocation/DiskThresholdMonitor.java

@@ -56,6 +56,12 @@ public class DiskThresholdMonitor {
 
     private static final Logger logger = LogManager.getLogger(DiskThresholdMonitor.class);
 
+    private static final Settings READ_ONLY_ALLOW_DELETE_SETTINGS = Settings.builder()
+        .put(IndexMetadata.SETTING_READ_ONLY_ALLOW_DELETE, Boolean.TRUE.toString()).build();
+
+    private static final Settings NOT_READ_ONLY_ALLOW_DELETE_SETTINGS =
+        Settings.builder().putNull(IndexMetadata.SETTING_READ_ONLY_ALLOW_DELETE).build();
+
     private final DiskThresholdSettings diskThresholdSettings;
     private final Client client;
     private final Supplier<ClusterState> clusterStateSupplier;
@@ -351,9 +357,7 @@ protected void updateIndicesReadOnly(Set<String> indicesToUpdate, ActionListener
             setLastRunTimeMillis();
             listener.onFailure(e);
         });
-        Settings readOnlySettings = readOnly ? Settings.builder()
-            .put(IndexMetadata.SETTING_READ_ONLY_ALLOW_DELETE, Boolean.TRUE.toString()).build() :
-            Settings.builder().putNull(IndexMetadata.SETTING_READ_ONLY_ALLOW_DELETE).build();
+        Settings readOnlySettings = readOnly ? READ_ONLY_ALLOW_DELETE_SETTINGS : NOT_READ_ONLY_ALLOW_DELETE_SETTINGS;
         client.admin().indices().prepareUpdateSettings(indicesToUpdate.toArray(Strings.EMPTY_ARRAY))
             .setSettings(readOnlySettings)
             .execute(wrappedListener.map(r -> null));

server/src/main/java/org/elasticsearch/common/settings/Settings.java

@@ -731,8 +731,6 @@ public Set<String> keySet() {
      */
     public static class Builder {
 
-        public static final Settings EMPTY_SETTINGS = new Builder().build();
-
         // we use a sorted map for consistent serialization when using getAsMap()
         private final Map<String, Object> map = new TreeMap<>();
 

server/src/main/java/org/elasticsearch/index/analysis/AnalysisRegistry.java

@@ -532,7 +532,7 @@ public IndexAnalyzers build(IndexSettings indexSettings,
         if (analyzers.containsKey(DEFAULT_ANALYZER_NAME) == false) {
             analyzers.put(DEFAULT_ANALYZER_NAME,
                     produceAnalyzer(DEFAULT_ANALYZER_NAME,
-                            new StandardAnalyzerProvider(indexSettings, null, DEFAULT_ANALYZER_NAME, Settings.Builder.EMPTY_SETTINGS),
+                            new StandardAnalyzerProvider(indexSettings, null, DEFAULT_ANALYZER_NAME, Settings.EMPTY),
                             tokenFilterFactoryFactories, charFilterFactoryFactories, tokenizerFactoryFactories));
         }
         NamedAnalyzer defaultAnalyzer = analyzers.get(DEFAULT_ANALYZER_NAME);