WIP

Author: nielsbauman

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

@@ -21,6 +21,7 @@
 import org.apache.lucene.index.LiveIndexWriterConfig;
 import org.apache.lucene.index.MergePolicy;
 import org.apache.lucene.index.MergeScheduler;
+import org.apache.lucene.index.MergeTrigger;
 import org.apache.lucene.index.SegmentCommitInfo;
 import org.apache.lucene.index.SegmentInfos;
 import org.apache.lucene.index.SoftDeletesRetentionMergePolicy;
@@ -2549,27 +2550,30 @@ public boolean forceMergeIsNoOp(int maxNumSegments, boolean onlyExpungeDeletes)
         if (onlyExpungeDeletes && maxNumSegments >= 0) {
             throw new IllegalArgumentException("only_expunge_deletes and max_num_segments are mutually exclusive");
         }
-        // TODO: is there a way for us to determine no-op with no max num segments?
-        if (maxNumSegments <= 0) {
-            return false;
-        }
         try (var reader = DirectoryReader.open(indexWriter)) {
             final var segmentCommitInfos = SegmentInfos.readCommit(reader.directory(), reader.getIndexCommit().getSegmentsFileName());
-            final var segmentsToMerge = new HashMap<SegmentCommitInfo, Boolean>();
-            for (int i = 0; i < segmentCommitInfos.size(); i++) {
-                final var segmentInfo = segmentCommitInfos.info(i);
-                if (onlyExpungeDeletes && segmentInfo.hasDeletions()) {
-                    return false;
+            final MergePolicy.MergeSpecification mergeSpecification;
+            if (maxNumSegments < 0) {
+                mergeSpecification = indexWriter.getConfig()
+                    .getMergePolicy()
+                    .findMerges(MergeTrigger.EXPLICIT, segmentCommitInfos, indexWriter);
+            } else {
+                final var segmentsToMerge = new HashMap<SegmentCommitInfo, Boolean>();
+                for (int i = 0; i < segmentCommitInfos.size(); i++) {
+                    final var segmentInfo = segmentCommitInfos.info(i);
+                    if (onlyExpungeDeletes && segmentInfo.hasDeletions()) {
+                        return false;
+                    }
+                    segmentsToMerge.put(segmentInfo, Boolean.TRUE);
                 }
-                segmentsToMerge.put(segmentInfo, Boolean.TRUE);
-            }
 
-            if (onlyExpungeDeletes) {
-                return true;
+                if (onlyExpungeDeletes) {
+                    return true;
+                }
+                mergeSpecification = indexWriter.getConfig()
+                    .getMergePolicy()
+                    .findForcedMerges(segmentCommitInfos, maxNumSegments, segmentsToMerge, indexWriter);
             }
-            final var mergeSpecification = indexWriter.getConfig()
-                .getMergePolicy()
-                .findForcedMerges(segmentCommitInfos, maxNumSegments, segmentsToMerge, indexWriter);
             return mergeSpecification == null || mergeSpecification.merges.isEmpty();
         }
     }