diff --git a/hyracks-fullstack/hyracks/hyracks-storage-am-lsm-btree/src/main/java/org/apache/hyracks/storage/am/lsm/btree/impls/ExternalBTree.java b/hyracks-fullstack/hyracks/hyracks-storage-am-lsm-btree/src/main/java/org/apache/hyracks/storage/am/lsm/btree/impls/ExternalBTree.java
index 8be75be..2be5125 100644
--- a/hyracks-fullstack/hyracks/hyracks-storage-am-lsm-btree/src/main/java/org/apache/hyracks/storage/am/lsm/btree/impls/ExternalBTree.java
+++ b/hyracks-fullstack/hyracks/hyracks-storage-am-lsm-btree/src/main/java/org/apache/hyracks/storage/am/lsm/btree/impls/ExternalBTree.java
@@ -188,8 +188,8 @@
             }
         }
         LSMBTreeRangeSearchCursor cursor = new LSMBTreeRangeSearchCursor(opCtx, returnDeletedTuples);
-        BTree firstBTree = ((LSMBTreeDiskComponent) mergingComponents.get(0)).getIndex();
-        BTree lastBTree = ((LSMBTreeDiskComponent) mergingComponents.get(mergingComponents.size() - 1)).getIndex();
+        BTree lastBTree = ((LSMBTreeDiskComponent) mergingComponents.get(0)).getIndex();
+        BTree firstBTree = ((LSMBTreeDiskComponent) mergingComponents.get(mergingComponents.size() - 1)).getIndex();
         FileReference firstFile = firstBTree.getFileReference();
         FileReference lastFile = lastBTree.getFileReference();
         LSMComponentFileReferences relMergeFileRefs =
diff --git a/hyracks-fullstack/hyracks/hyracks-storage-am-lsm-btree/src/main/java/org/apache/hyracks/storage/am/lsm/btree/impls/ExternalBTreeWithBuddy.java b/hyracks-fullstack/hyracks/hyracks-storage-am-lsm-btree/src/main/java/org/apache/hyracks/storage/am/lsm/btree/impls/ExternalBTreeWithBuddy.java
index 5bcf30d..be91244 100644
--- a/hyracks-fullstack/hyracks/hyracks-storage-am-lsm-btree/src/main/java/org/apache/hyracks/storage/am/lsm/btree/impls/ExternalBTreeWithBuddy.java
+++ b/hyracks-fullstack/hyracks/hyracks-storage-am-lsm-btree/src/main/java/org/apache/hyracks/storage/am/lsm/btree/impls/ExternalBTreeWithBuddy.java
@@ -256,8 +256,8 @@
 
     protected LSMComponentFileReferences getMergeTargetFileName(List<ILSMComponent> mergingDiskComponents)
             throws HyracksDataException {
-        BTree firstTree = ((LSMBTreeWithBuddyDiskComponent) mergingDiskComponents.get(0)).getIndex();
-        BTree lastTree = ((LSMBTreeWithBuddyDiskComponent) mergingDiskComponents.get(mergingDiskComponents.size() - 1))
+        BTree lastTree = ((LSMBTreeWithBuddyDiskComponent) mergingDiskComponents.get(0)).getIndex();
+        BTree firstTree = ((LSMBTreeWithBuddyDiskComponent) mergingDiskComponents.get(mergingDiskComponents.size() - 1))
                 .getIndex();
         FileReference firstFile = firstTree.getFileReference();
         FileReference lastFile = lastTree.getFileReference();
diff --git a/hyracks-fullstack/hyracks/hyracks-storage-am-lsm-common/src/main/java/org/apache/hyracks/storage/am/lsm/common/impls/AbstractLSMIndex.java b/hyracks-fullstack/hyracks/hyracks-storage-am-lsm-common/src/main/java/org/apache/hyracks/storage/am/lsm/common/impls/AbstractLSMIndex.java
index 377a218..3d928a4 100644
--- a/hyracks-fullstack/hyracks/hyracks-storage-am-lsm-common/src/main/java/org/apache/hyracks/storage/am/lsm/common/impls/AbstractLSMIndex.java
+++ b/hyracks-fullstack/hyracks/hyracks-storage-am-lsm-common/src/main/java/org/apache/hyracks/storage/am/lsm/common/impls/AbstractLSMIndex.java
@@ -400,8 +400,8 @@
         mergeCtx.getComponentHolder().addAll(mergingComponents);
         propagateMap(ctx, mergeCtx);
         mergingComponents.stream().forEach(mergeCtx.getComponentsToBeMerged()::add);
-        ILSMDiskComponent firstComponent = mergingComponents.get(0);
-        ILSMDiskComponent lastComponent = mergingComponents.get(mergingComponents.size() - 1);
+        ILSMDiskComponent lastComponent = mergingComponents.get(0);
+        ILSMDiskComponent firstComponent = mergingComponents.get(mergingComponents.size() - 1);
         LSMComponentFileReferences mergeFileRefs = getMergeFileReferences(firstComponent, lastComponent);
         ILSMIOOperation mergeOp =
                 TracedIOOperation.wrap(createMergeOperation(mergeCtx, mergeFileRefs, ioOpCallback), tracer);
diff --git a/hyracks-fullstack/hyracks/hyracks-storage-am-lsm-common/src/main/java/org/apache/hyracks/storage/am/lsm/common/impls/AbstractLSMIndexFileManager.java b/hyracks-fullstack/hyracks/hyracks-storage-am-lsm-common/src/main/java/org/apache/hyracks/storage/am/lsm/common/impls/AbstractLSMIndexFileManager.java
index 42d3f56..57fd01d 100644
--- a/hyracks-fullstack/hyracks/hyracks-storage-am-lsm-common/src/main/java/org/apache/hyracks/storage/am/lsm/common/impls/AbstractLSMIndexFileManager.java
+++ b/hyracks-fullstack/hyracks/hyracks-storage-am-lsm-common/src/main/java/org/apache/hyracks/storage/am/lsm/common/impls/AbstractLSMIndexFileManager.java
@@ -208,9 +208,14 @@
             throws HyracksDataException {
         String[] firstTimestampRange = firstFileName.split(DELIMITER);
         String[] lastTimestampRange = lastFileName.split(DELIMITER);
+        String start = firstTimestampRange[0];
+        String end = lastTimestampRange[1];
+        if (end.compareTo(start) <= 0) {
+            throw new IllegalArgumentException(
+                    "A Merge file must have end greater than start. Found end: " + end + " and start: " + start);
+        }
         // Get the range of timestamps by taking the earliest and the latest timestamps
-        return new LSMComponentFileReferences(
-                baseDir.getChild(firstTimestampRange[0] + DELIMITER + lastTimestampRange[1]), null, null);
+        return new LSMComponentFileReferences(baseDir.getChild(start + DELIMITER + end), null, null);
     }
 
     @Override
@@ -327,6 +332,12 @@
             }
             return b.interval[1].compareTo(interval[1]);
         }
+
+        @Override
+        public String toString() {
+            return "{\"type\" : \"" + (interval[0].equals(interval[1]) ? "flush" : "merge") + "\", \"start\" : \""
+                    + interval[0] + "\", \"end\" : \"" + interval[1] + "\"}";
+        }
     }
 
     private class RecencyComparator implements Comparator<ComparableFileName> {
diff --git a/hyracks-fullstack/hyracks/hyracks-storage-am-lsm-common/src/main/java/org/apache/hyracks/storage/am/lsm/common/impls/LSMComponentFileReferences.java b/hyracks-fullstack/hyracks/hyracks-storage-am-lsm-common/src/main/java/org/apache/hyracks/storage/am/lsm/common/impls/LSMComponentFileReferences.java
index 4dd57eb..9346b56 100644
--- a/hyracks-fullstack/hyracks/hyracks-storage-am-lsm-common/src/main/java/org/apache/hyracks/storage/am/lsm/common/impls/LSMComponentFileReferences.java
+++ b/hyracks-fullstack/hyracks/hyracks-storage-am-lsm-common/src/main/java/org/apache/hyracks/storage/am/lsm/common/impls/LSMComponentFileReferences.java
@@ -53,4 +53,10 @@
     public FileReference[] getFileReferences() {
         return new FileReference[] { insertIndexFileReference, deleteIndexFileReference, bloomFilterFileReference };
     }
+
+    @Override
+    public String toString() {
+        return "{ \"insert\" : \"" + insertIndexFileReference + "\", \"delete\" : \"" + deleteIndexFileReference
+                + "\", \"bloom\" : \"" + bloomFilterFileReference + "\"}";
+    }
 }
diff --git a/hyracks-fullstack/hyracks/hyracks-storage-am-lsm-rtree/src/main/java/org/apache/hyracks/storage/am/lsm/rtree/impls/ExternalRTree.java b/hyracks-fullstack/hyracks/hyracks-storage-am-lsm-rtree/src/main/java/org/apache/hyracks/storage/am/lsm/rtree/impls/ExternalRTree.java
index 5e8bd0b..015f34c 100644
--- a/hyracks-fullstack/hyracks/hyracks-storage-am-lsm-rtree/src/main/java/org/apache/hyracks/storage/am/lsm/rtree/impls/ExternalRTree.java
+++ b/hyracks-fullstack/hyracks/hyracks-storage-am-lsm-rtree/src/main/java/org/apache/hyracks/storage/am/lsm/rtree/impls/ExternalRTree.java
@@ -559,8 +559,8 @@
         List<ILSMComponent> mergingComponents = ctx.getComponentHolder();
         LSMRTreeSortedCursor cursor = new LSMRTreeSortedCursor(rctx, linearizer, buddyBTreeFields);
         LSMComponentFileReferences relMergeFileRefs =
-                getMergeFileReferences((ILSMDiskComponent) mergingComponents.get(0),
-                        (ILSMDiskComponent) mergingComponents.get(mergingComponents.size() - 1));
+                getMergeFileReferences((ILSMDiskComponent) mergingComponents.get(mergingComponents.size() - 1),
+                        (ILSMDiskComponent) mergingComponents.get(0));
         ILSMIndexAccessor accessor = new LSMRTreeAccessor(getHarness(), rctx, buddyBTreeFields);
         // create the merge operation.
         LSMRTreeMergeOperation mergeOp =