Take only_expunge_deletes into account

Author: nielsbauman

server/src/main/java/org/elasticsearch/action/admin/indices/forcemerge/TransportForceMergeAction.java

@@ -108,7 +108,7 @@ protected void shardOperation(
         }).<EmptyResult>andThen((l, indexShard) -> {
             boolean forceMergeIsNoOp = indexShard.withEngineException(engine -> {
                 engine.flush();
-                return engine.forceMergeIsNoOp(request.maxNumSegments());
+                return engine.forceMergeIsNoOp(request.maxNumSegments(), request.onlyExpungeDeletes());
             });
             if (forceMergeIsNoOp) {
                 logger.info("---> skipping force merge for shard {} since it is a no-op", indexShard.shardId());

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

@@ -1540,7 +1540,7 @@ public final void flush() throws EngineException {
     public abstract void forceMerge(boolean flush, int maxNumSegments, boolean onlyExpungeDeletes, String forceMergeUUID)
         throws EngineException, IOException;
 
-    public abstract boolean forceMergeIsNoOp(int maxNumSegments) throws IOException;
+    public abstract boolean forceMergeIsNoOp(int maxNumSegments, boolean onlyExpungeDeletes) throws IOException;
 
     /**
      * Snapshots the most recent index and returns a handle to it. If needed will try and "commit" the

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

@@ -2545,7 +2545,10 @@ public void forceMerge(final boolean flush, int maxNumSegments, boolean onlyExpu
     }
 
     @Override
-    public boolean forceMergeIsNoOp(int maxNumSegments) throws IOException {
+    public boolean forceMergeIsNoOp(int maxNumSegments, boolean onlyExpungeDeletes) throws IOException {
+        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;
@@ -2554,9 +2557,16 @@ public boolean forceMergeIsNoOp(int maxNumSegments) throws IOException {
             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++) {
-                segmentsToMerge.put(segmentCommitInfos.info(i), Boolean.TRUE);
+                final var segmentInfo = segmentCommitInfos.info(i);
+                if (onlyExpungeDeletes && segmentInfo.hasDeletions()) {
+                    return false;
+                }
+                segmentsToMerge.put(segmentInfo, Boolean.TRUE);
             }
 
+            if (onlyExpungeDeletes) {
+                return true;
+            }
             final var mergeSpecification = indexWriter.getConfig()
                 .getMergePolicy()
                 .findForcedMerges(segmentCommitInfos, maxNumSegments, segmentsToMerge, indexWriter);

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

@@ -479,7 +479,7 @@ public void forceMerge(boolean flush, int maxNumSegments, boolean onlyExpungeDel
     }
 
     @Override
-    public boolean forceMergeIsNoOp(int maxNumSegments) throws IOException {
+    public boolean forceMergeIsNoOp(int maxNumSegments, boolean onlyExpungeDeletes) throws IOException {
         throw new UnsupportedOperationException(
             "force merge is not supported on a read-only engine, "
                 + "target max number of segments["