Add segment replication index setting, gated by feature flag

Signed-off-by: Kartik Ganesh <[email protected]>

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

@@ -260,6 +260,17 @@ public Iterator<Setting<?>> settings() {
         Property.IndexScope
     );
 
+    public static final String SETTING_SEGMENT_REPLICATION = "index.replication.segment_replication";
+    /**
+     * Used to specify if the index should use segment replication. If false, document replication is used.
+     */
+    public static final Setting<Boolean> INDEX_SEGMENT_REPLICATION_SETTING = Setting.boolSetting(
+        SETTING_SEGMENT_REPLICATION,
+        false,
+        Property.IndexScope,
+        Property.Final
+    );
+
     public static final String SETTING_AUTO_EXPAND_REPLICAS = "index.auto_expand_replicas";
     public static final Setting<AutoExpandReplicas> INDEX_AUTO_EXPAND_REPLICAS_SETTING = AutoExpandReplicas.SETTING;
 

server/src/main/java/org/opensearch/index/IndexSettings.java

@@ -530,6 +530,7 @@ public final class IndexSettings {
     private final String nodeName;
     private final Settings nodeSettings;
     private final int numberOfShards;
+    private final Boolean isSegRepEnabled;
     // volatile fields are updated via #updateIndexMetadata(IndexMetadata) under lock
     private volatile Settings settings;
     private volatile IndexMetadata indexMetadata;
@@ -681,6 +682,7 @@ public IndexSettings(final IndexMetadata indexMetadata, final Settings nodeSetti
         nodeName = Node.NODE_NAME_SETTING.get(settings);
         this.indexMetadata = indexMetadata;
         numberOfShards = settings.getAsInt(IndexMetadata.SETTING_NUMBER_OF_SHARDS, null);
+        isSegRepEnabled = settings.getAsBoolean(IndexMetadata.SETTING_SEGMENT_REPLICATION, false);
 
         this.searchThrottled = INDEX_SEARCH_THROTTLED.get(settings);
         this.queryStringLenient = QUERY_STRING_LENIENT_SETTING.get(settings);
@@ -915,6 +917,13 @@ public int getNumberOfReplicas() {
         return settings.getAsInt(IndexMetadata.SETTING_NUMBER_OF_REPLICAS, null);
     }
 
+    /**
+     * Returns true if segment replication is enabled on the index.
+     */
+    public boolean isSegrepEnabled() {
+        return Boolean.TRUE.equals(isSegRepEnabled);
+    }
+
     /**
      * Returns the node settings. The settings returned from {@link #getSettings()} are a merged version of the
      * index settings and the node settings where node settings are overwritten by index settings.

server/src/main/java/org/opensearch/node/Node.java

@@ -255,6 +255,27 @@ public class Node implements Closeable {
         Property.NodeScope
     );
 
+    /**
+     * Feature flag to gate the visibility of the index setting that enables segment replication.
+     * Once the feature is ready for production release, this feature flag can be removed.
+     */
+    public static final boolean SEGREP_FEATURE_FLAG_ENABLED = "true".equals(
+        System.getProperty("opensearch.segment_replication_feature_flag_enabled")
+    );
+
+    /**
+     * Used to specify if the index should use segment replication. If false, document replication is used.
+     * Currently located here so that it can gated by the {@link #SEGREP_FEATURE_FLAG_ENABLED} feature flag.
+     * Once the feature is ready for production release, the setting can be moved to
+     * {@link org.opensearch.common.settings.IndexScopedSettings#BUILT_IN_INDEX_SETTINGS}.
+     */
+    private static final Setting<Boolean> INDEX_SEGMENT_REPLICATION_SETTING = Setting.boolSetting(
+        "index.replication.segment_replication",
+        false,
+        Property.IndexScope,
+        Property.Final
+    );
+
     /**
     * controls whether the node is allowed to persist things like metadata to disk
     * Note that this does not control whether the node stores actual indices (see
@@ -457,6 +478,10 @@ protected Node(
             for (final ExecutorBuilder<?> builder : threadPool.builders()) {
                 additionalSettings.addAll(builder.getRegisteredSettings());
             }
+            // Add segment replication setting gated by feature flag
+            if (SEGREP_FEATURE_FLAG_ENABLED) {
+                additionalSettings.add(INDEX_SEGMENT_REPLICATION_SETTING);
+            }
             client = new NodeClient(settings, threadPool);
 
             final ScriptModule scriptModule = new ScriptModule(settings, pluginsService.filterPlugins(ScriptPlugin.class));