Remove track_postings_in_memory_bytes feature flag (#133583)

Follow-up to #129969 to remove the feature flag.

Author: jordan-powers

server/src/main/java/org/elasticsearch/index/codec/TrackingPostingsInMemoryBytesCodec.java

@@ -24,7 +24,6 @@
 import org.apache.lucene.index.TermsEnum;
 import org.apache.lucene.internal.hppc.IntHashSet;
 import org.apache.lucene.util.BytesRef;
-import org.elasticsearch.common.util.FeatureFlag;
 
 import java.io.IOException;
 import java.util.function.IntConsumer;
@@ -34,8 +33,6 @@
  * {@link org.apache.lucene.codecs.lucene90.blocktree.FieldReader} keeps an in-memory reference to the min and max term.
  */
 public class TrackingPostingsInMemoryBytesCodec extends FilterCodec {
-    public static final FeatureFlag TRACK_POSTINGS_IN_MEMORY_BYTES = new FeatureFlag("track_postings_in_memory_bytes");
-
     public static final String IN_MEMORY_POSTINGS_BYTES_KEY = "es.postings.in_memory_bytes";
 
     public TrackingPostingsInMemoryBytesCodec(Codec delegate) {

server/src/main/java/org/elasticsearch/index/engine/Engine.java

@@ -44,6 +44,7 @@
 import org.elasticsearch.action.support.PlainActionFuture;
 import org.elasticsearch.action.support.SubscribableListener;
 import org.elasticsearch.action.support.UnsafePlainActionFuture;
+import org.elasticsearch.cluster.node.DiscoveryNode;
 import org.elasticsearch.cluster.service.ClusterApplierService;
 import org.elasticsearch.common.bytes.BytesReference;
 import org.elasticsearch.common.logging.Loggers;
@@ -161,6 +162,8 @@ public abstract class Engine implements Closeable {
     private final RefCounted ensureOpenRefs = AbstractRefCounted.of(() -> drainOnCloseListener.onResponse(null));
     private final Releasable releaseEnsureOpenRef = ensureOpenRefs::decRef; // reuse this to avoid allocation for each op
 
+    private final boolean isStateless;
+
     /*
      * on {@code lastWriteNanos} we use System.nanoTime() to initialize this since:
      *  - we use the value for figuring out if the shard / engine is active so if we startup and no write has happened yet we still
@@ -189,6 +192,8 @@ protected Engine(EngineConfig engineConfig) {
         this.pauseIndexingOnThrottle = IndexingMemoryController.PAUSE_INDEXING_ON_THROTTLE.get(
             engineConfig.getIndexSettings().getSettings()
         );
+
+        this.isStateless = DiscoveryNode.isStateless(engineConfig.getIndexSettings().getNodeSettings());
     }
 
     /**
@@ -266,7 +271,7 @@ protected final DocsStats docsStats(IndexReader indexReader) {
      */
     public ShardFieldStats shardFieldStats() {
         try (var searcher = acquireSearcher("shard_field_stats", Engine.SearcherScope.INTERNAL)) {
-            return shardFieldStats(searcher.getLeafContexts());
+            return shardFieldStats(searcher.getLeafContexts(), isStateless);
         }
     }
 
@@ -279,7 +284,7 @@ public FieldInfos shardFieldInfos() {
         }
     }
 
-    protected static ShardFieldStats shardFieldStats(List<LeafReaderContext> leaves) {
+    protected static ShardFieldStats shardFieldStats(List<LeafReaderContext> leaves, boolean isStateless) {
         int numSegments = 0;
         int totalFields = 0;
         long usages = 0;
@@ -296,7 +301,7 @@ protected static ShardFieldStats shardFieldStats(List<LeafReaderContext> leaves)
             } else {
                 usages = -1;
             }
-            boolean trackPostingsMemoryEnabled = TrackingPostingsInMemoryBytesCodec.TRACK_POSTINGS_IN_MEMORY_BYTES.isEnabled();
+            boolean trackPostingsMemoryEnabled = isStateless;
             boolean trackLiveDocsMemoryEnabled = ShardFieldStats.TRACK_LIVE_DOCS_IN_MEMORY_BYTES.isEnabled();
             if (trackLiveDocsMemoryEnabled || trackPostingsMemoryEnabled) {
                 SegmentReader segmentReader = Lucene.tryUnwrapSegmentReader(leaf.reader());

server/src/main/java/org/elasticsearch/index/engine/InternalEngine.java

@@ -46,6 +46,7 @@
 import org.elasticsearch.action.support.PlainActionFuture;
 import org.elasticsearch.action.support.SubscribableListener;
 import org.elasticsearch.cluster.metadata.DataStream;
+import org.elasticsearch.cluster.node.DiscoveryNode;
 import org.elasticsearch.cluster.service.ClusterApplierService;
 import org.elasticsearch.common.ReferenceDocs;
 import org.elasticsearch.common.Strings;
@@ -2807,7 +2808,7 @@ private IndexWriterConfig getIndexWriterConfig() {
         iwc.setRAMBufferSizeMB(engineConfig.getIndexingBufferSize().getMbFrac());
 
         Codec codec = engineConfig.getCodec();
-        if (TrackingPostingsInMemoryBytesCodec.TRACK_POSTINGS_IN_MEMORY_BYTES.isEnabled()) {
+        if (DiscoveryNode.isStateless(engineConfig.getIndexSettings().getNodeSettings())) {
             codec = new TrackingPostingsInMemoryBytesCodec(codec);
         }
         iwc.setCodec(codec);

server/src/test/java/org/elasticsearch/index/shard/IndexShardTests.java

@@ -80,7 +80,6 @@
 import org.elasticsearch.index.IndexVersion;
 import org.elasticsearch.index.MergePolicyConfig;
 import org.elasticsearch.index.codec.CodecService;
-import org.elasticsearch.index.codec.TrackingPostingsInMemoryBytesCodec;
 import org.elasticsearch.index.engine.CommitStats;
 import org.elasticsearch.index.engine.DocIdSeqNoAndSource;
 import org.elasticsearch.index.engine.Engine;
@@ -1887,7 +1886,7 @@ public void testShardFieldStats() throws IOException {
         assertThat(stats.fieldUsages(), equalTo(0L));
         assertThat(stats.postingsInMemoryBytes(), equalTo(0L));
 
-        boolean postingsBytesTrackingEnabled = TrackingPostingsInMemoryBytesCodec.TRACK_POSTINGS_IN_MEMORY_BYTES.isEnabled();
+        boolean postingsBytesTrackingEnabled = DiscoveryNode.isStateless(shard.indexSettings().getNodeSettings());
 
         // index some documents
         int numDocs = between(2, 10);