Revert "Temporarily disable use_default_lucene_postings_format feature flag. …" (#128433)

This reverts commit 6f2d4c816a303e27b0bd431cc5c165333ceda5e3.

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

@@ -50,10 +50,8 @@ public class PerFieldFormatSupplier {
         this.mapperService = mapperService;
         this.bloomFilterPostingsFormat = new ES87BloomFilterPostingsFormat(bigArrays, this::internalGetPostingsFormatForField);
 
-        // TODO: temporarily disable feature flag for a few days to see effect in benchmarks
-        boolean useDefaultLucenePostingsFormat = USE_DEFAULT_LUCENE_POSTINGS_FORMAT.isEnabled() && false;
         if (mapperService != null
-            && useDefaultLucenePostingsFormat
+            && USE_DEFAULT_LUCENE_POSTINGS_FORMAT.isEnabled()
             && mapperService.getIndexSettings().getIndexVersionCreated().onOrAfter(IndexVersions.USE_LUCENE101_POSTINGS_FORMAT)
             && mapperService.getIndexSettings().getMode() == IndexMode.STANDARD) {
             defaultPostingsFormat = Elasticsearch900Lucene101Codec.DEFAULT_POSTINGS_FORMAT;

server/src/test/java/org/elasticsearch/index/codec/PerFieldMapperCodecTests.java

@@ -10,6 +10,7 @@
 package org.elasticsearch.index.codec;
 
 import org.apache.lucene.codecs.PostingsFormat;
+import org.apache.lucene.codecs.lucene101.Lucene101PostingsFormat;
 import org.elasticsearch.cluster.metadata.IndexMetadata;
 import org.elasticsearch.common.compress.CompressedXContent;
 import org.elasticsearch.common.settings.Settings;
@@ -93,7 +94,8 @@ public class PerFieldMapperCodecTests extends ESTestCase {
         assertThat(perFieldMapperCodec.getPostingsFormatForField("_id"), instanceOf(ES87BloomFilterPostingsFormat.class));
         assertThat(perFieldMapperCodec.useBloomFilter("another_field"), is(false));
 
-        Class<? extends PostingsFormat> expectedPostingsFormat = ES812PostingsFormat.class;
+        Class<? extends PostingsFormat> expectedPostingsFormat = PerFieldFormatSupplier.USE_DEFAULT_LUCENE_POSTINGS_FORMAT.isEnabled()
+            && timeSeries == false ? Lucene101PostingsFormat.class : ES812PostingsFormat.class;
         assertThat(perFieldMapperCodec.getPostingsFormatForField("another_field"), instanceOf(expectedPostingsFormat));
     }
 
@@ -108,7 +110,9 @@ public class PerFieldMapperCodecTests extends ESTestCase {
     public void testUseBloomFilterWithTimestampFieldEnabled_noTimeSeriesMode() throws IOException {
         PerFieldFormatSupplier perFieldMapperCodec = createFormatSupplier(true, false, false);
         assertThat(perFieldMapperCodec.useBloomFilter("_id"), is(false));
-        Class<? extends PostingsFormat> expectedPostingsFormat = ES812PostingsFormat.class;
+        Class<? extends PostingsFormat> expectedPostingsFormat = PerFieldFormatSupplier.USE_DEFAULT_LUCENE_POSTINGS_FORMAT.isEnabled()
+            ? Lucene101PostingsFormat.class
+            : ES812PostingsFormat.class;
         assertThat(perFieldMapperCodec.getPostingsFormatForField("_id"), instanceOf(expectedPostingsFormat));
     }