Update readCommit for N-2

Author: ChrisHegarty

server/src/main/java/org/elasticsearch/common/lucene/Lucene.java

@@ -70,7 +70,6 @@
 import org.elasticsearch.common.util.iterable.Iterables;
 import org.elasticsearch.core.Nullable;
 import org.elasticsearch.core.SuppressForbidden;
-import org.elasticsearch.index.IndexVersion;
 import org.elasticsearch.index.IndexVersions;
 import org.elasticsearch.index.analysis.AnalyzerScope;
 import org.elasticsearch.index.analysis.NamedAnalyzer;
@@ -89,9 +88,11 @@
 import java.util.Map;
 import java.util.Objects;
 
-import static org.apache.lucene.util.Version.LUCENE_10_0_0;
-
 public class Lucene {
+
+    // Support for reading N-2
+    public static final int MIN_SUPPORTED_MAJOR = Version.LATEST.major - 2;
+
     public static final String LATEST_CODEC = "Lucene101";
 
     public static final String SOFT_DELETES_FIELD = "__soft_deletes";
@@ -156,25 +157,7 @@ public static SegmentInfos readSegmentInfos(IndexCommit commit) throws IOExcepti
      * Reads the segments infos from the given segments file name, failing if it fails to load
      */
     private static SegmentInfos readSegmentInfos(String segmentsFileName, Directory directory) throws IOException {
-        // TODO Use readCommit(Directory directory, String segmentFileName, int minSupportedMajorVersion) once Lucene 10.1 is available
-        // and remove the try-catch block for IndexFormatTooOldException
-        assert IndexVersion.current().luceneVersion().equals(LUCENE_10_0_0) : "remove the try-catch block below";
-        try {
-            return SegmentInfos.readCommit(directory, segmentsFileName);
-        } catch (IndexFormatTooOldException e) {
-            try {
-                // Temporary workaround until Lucene 10.1 is available: try to leverage min. read-only compatibility to read the last commit
-                // and then check if this is the commit we want. This should always work for the case we are interested in (archive and
-                // searchable snapshots indices in N-2 version) as no newer commit should be ever written.
-                var segmentInfos = readSegmentInfos(directory);
-                if (segmentsFileName.equals(segmentInfos.getSegmentsFileName())) {
-                    return segmentInfos;
-                }
-            } catch (Exception suppressed) {
-                e.addSuppressed(suppressed);
-            }
-            throw e;
-        }
+        return SegmentInfos.readCommit(directory, segmentsFileName, MIN_SUPPORTED_MAJOR);
     }
 
     /**

server/src/main/java/org/elasticsearch/index/IndexVersions.java

@@ -138,7 +138,6 @@ private static Version parseUnchecked(String version) {
     public static final IndexVersion TIME_BASED_K_ORDERED_DOC_ID = def(9_002_00_0, Version.LUCENE_10_0_0);
     public static final IndexVersion DEPRECATE_SOURCE_MODE_MAPPER = def(9_003_00_0, Version.LUCENE_10_0_0);
     public static final IndexVersion USE_SYNTHETIC_SOURCE_FOR_RECOVERY = def(9_004_00_0, Version.LUCENE_10_0_0);
-
     public static final IndexVersion UPGRADE_TO_LUCENE_10_1_0 = def(9_005_00_0, Version.LUCENE_10_1_0);
 
     /*