fix

Author: JingsongLi

paimon-common/src/main/java/org/apache/paimon/lookup/sort/db/LsmCompactor.java

@@ -313,9 +313,9 @@ private MergeResult mergeSortedRuns(
                 SstFileMetadata singleFile = group.get(0);
                 boolean canSkip = !dropTombstones || !singleFile.hasTombstones();
                 if (canSkip) {
-                    singleFile.setLevel(outputLevel);
-                    outputFiles.add(singleFile);
-                    skippedFileSet.add(singleFile.getFile());
+                    SstFileMetadata promoted = singleFile.withLevel(outputLevel);
+                    outputFiles.add(promoted);
+                    skippedFileSet.add(promoted.getFile());
                     skippedGroupCount++;
                     continue;
                 }

paimon-common/src/main/java/org/apache/paimon/lookup/sort/db/SstFileMetadata.java

@@ -34,9 +34,7 @@ public final class SstFileMetadata {
     private final MemorySlice maxKey;
     private final long fileSize;
     private final long tombstoneCount;
-
-    /** The level this file belongs to in the LSM tree. Mutable because compaction reassigns it. */
-    private int level;
+    private final int level;
 
     public SstFileMetadata(
             File file, MemorySlice minKey, MemorySlice maxKey, long tombstoneCount, int level) {
@@ -78,8 +76,8 @@ public int getLevel() {
         return level;
     }
 
-    public void setLevel(int level) {
-        this.level = level;
+    public SstFileMetadata withLevel(int newLevel) {
+        return new SstFileMetadata(file, minKey, maxKey, fileSize, tombstoneCount, newLevel);
     }
 
     public boolean hasTombstones() {