diff --git a/hyracks/hyracks-storage-am-lsm-common/src/main/java/edu/uci/ics/hyracks/storage/am/lsm/common/api/ILSMIOOperationCallback.java b/hyracks/hyracks-storage-am-lsm-common/src/main/java/edu/uci/ics/hyracks/storage/am/lsm/common/api/ILSMIOOperationCallback.java
index 7086b59..9af08fa 100644
--- a/hyracks/hyracks-storage-am-lsm-common/src/main/java/edu/uci/ics/hyracks/storage/am/lsm/common/api/ILSMIOOperationCallback.java
+++ b/hyracks/hyracks-storage-am-lsm-common/src/main/java/edu/uci/ics/hyracks/storage/am/lsm/common/api/ILSMIOOperationCallback.java
@@ -17,12 +17,36 @@
 import java.util.List;
 
 import edu.uci.ics.hyracks.api.exceptions.HyracksDataException;
+import edu.uci.ics.hyracks.storage.am.lsm.common.impls.LSMOperationType;
 
 public interface ILSMIOOperationCallback {
-    public void beforeOperation() throws HyracksDataException;
 
-    public void afterOperation(List<ILSMComponent> oldComponents, ILSMComponent newComponent)
+    /**
+     * This method is called on an IO operation sometime before the operation is executed.
+     * (i.e. IO operations could be flush or merge operations.)
+     */
+    public void beforeOperation(LSMOperationType opType) throws HyracksDataException;
+
+    /**
+     * This method is called on an IO operation sometime after the operation was completed.
+     * (i.e. IO operations could be flush or merge operations.)
+     * 
+     * @param oldComponents
+     * @param newComponent
+     * @throws HyracksDataException
+     */
+    public void afterOperation(LSMOperationType opType, List<ILSMComponent> oldComponents, ILSMComponent newComponent)
             throws HyracksDataException;
 
-    public void afterFinalize(ILSMComponent newComponent) throws HyracksDataException;
+    /**
+     * This method is called on an IO operation when the operation needs any cleanup works
+     * regardless that the IO operation was executed or not. Once the IO operation is executed,
+     * this method should be called after ILSMIOOperationCallback.afterOperation() was called.
+     * 
+     * @param newComponent
+     * @throws HyracksDataException
+     */
+    public void afterFinalize(LSMOperationType opType, ILSMComponent newComponent) throws HyracksDataException;
+
+    public void setNumOfMutableComponents(int count);
 }
diff --git a/hyracks/hyracks-storage-am-lsm-common/src/main/java/edu/uci/ics/hyracks/storage/am/lsm/common/impls/AbstractLSMIndex.java b/hyracks/hyracks-storage-am-lsm-common/src/main/java/edu/uci/ics/hyracks/storage/am/lsm/common/impls/AbstractLSMIndex.java
index 8cfd96d..44bcfc2 100644
--- a/hyracks/hyracks-storage-am-lsm-common/src/main/java/edu/uci/ics/hyracks/storage/am/lsm/common/impls/AbstractLSMIndex.java
+++ b/hyracks/hyracks-storage-am-lsm-common/src/main/java/edu/uci/ics/hyracks/storage/am/lsm/common/impls/AbstractLSMIndex.java
@@ -43,7 +43,6 @@
     protected final ILSMHarness lsmHarness;
 
     protected final ILSMIOOperationScheduler ioScheduler;
-    //protected final ILSMIOOperationCallbackProvider ioOpCallbackProvider;
     protected final ILSMIOOperationCallback ioOpCallback;
 
     // In-memory components.   
@@ -73,6 +72,7 @@
         this.bloomFilterFalsePositiveRate = bloomFilterFalsePositiveRate;
         this.ioScheduler = ioScheduler;
         this.ioOpCallback = ioOpCallback;
+        this.ioOpCallback.setNumOfMutableComponents(virtualBufferCaches.size());
         lsmHarness = new LSMHarness(this, mergePolicy, opTracker);
         isActivated = false;
         diskComponents = new LinkedList<ILSMComponent>();
diff --git a/hyracks/hyracks-storage-am-lsm-common/src/main/java/edu/uci/ics/hyracks/storage/am/lsm/common/impls/BlockingIOOperationCallbackWrapper.java b/hyracks/hyracks-storage-am-lsm-common/src/main/java/edu/uci/ics/hyracks/storage/am/lsm/common/impls/BlockingIOOperationCallbackWrapper.java
index a7ca95f..fefe812 100644
--- a/hyracks/hyracks-storage-am-lsm-common/src/main/java/edu/uci/ics/hyracks/storage/am/lsm/common/impls/BlockingIOOperationCallbackWrapper.java
+++ b/hyracks/hyracks-storage-am-lsm-common/src/main/java/edu/uci/ics/hyracks/storage/am/lsm/common/impls/BlockingIOOperationCallbackWrapper.java
@@ -38,20 +38,25 @@
     }
 
     @Override
-    public void beforeOperation() throws HyracksDataException {
-        wrappedCallback.beforeOperation();
+    public void beforeOperation(LSMOperationType opType) throws HyracksDataException {
+        wrappedCallback.beforeOperation(opType);
     }
 
     @Override
-    public void afterOperation(List<ILSMComponent> oldComponents, ILSMComponent newComponent)
+    public void afterOperation(LSMOperationType opType, List<ILSMComponent> oldComponents, ILSMComponent newComponent)
             throws HyracksDataException {
-        wrappedCallback.afterOperation(oldComponents, newComponent);
+        wrappedCallback.afterOperation(opType, oldComponents, newComponent);
     }
 
     @Override
-    public synchronized void afterFinalize(ILSMComponent newComponent) throws HyracksDataException {
-        wrappedCallback.afterFinalize(newComponent);
+    public synchronized void afterFinalize(LSMOperationType opType, ILSMComponent newComponent) throws HyracksDataException {
+        wrappedCallback.afterFinalize(opType, newComponent);
         notifyAll();
         notified = true;
     }
+
+    @Override
+    public void setNumOfMutableComponents(int count) {
+        wrappedCallback.setNumOfMutableComponents(count);
+    }
 }
diff --git a/hyracks/hyracks-storage-am-lsm-common/src/main/java/edu/uci/ics/hyracks/storage/am/lsm/common/impls/LSMHarness.java b/hyracks/hyracks-storage-am-lsm-common/src/main/java/edu/uci/ics/hyracks/storage/am/lsm/common/impls/LSMHarness.java
index 145bfe9..ca775b7 100644
--- a/hyracks/hyracks-storage-am-lsm-common/src/main/java/edu/uci/ics/hyracks/storage/am/lsm/common/impls/LSMHarness.java
+++ b/hyracks/hyracks-storage-am-lsm-common/src/main/java/edu/uci/ics/hyracks/storage/am/lsm/common/impls/LSMHarness.java
@@ -118,6 +118,7 @@
         // Check if there is any action that is needed to be taken based on the operation type
         switch (opType) {
             case FLUSH:
+                lsmIndex.getIOOperationCallback().beforeOperation(LSMOperationType.FLUSH);
                 // Changing the flush status should *always* precede changing the mutable component.
                 lsmIndex.changeFlushStatusForCurrentMutableCompoent(false);
                 lsmIndex.changeMutableComponent();
@@ -125,6 +126,8 @@
                 // again if they can grab and enter the mutable component.
                 opTracker.notifyAll();
                 break;
+            case MERGE:
+                lsmIndex.getIOOperationCallback().beforeOperation(LSMOperationType.MERGE);
             default:
                 break;
         }
@@ -254,9 +257,7 @@
     public void scheduleFlush(ILSMIndexOperationContext ctx, ILSMIOOperationCallback callback)
             throws HyracksDataException {
         if (!getAndEnterComponents(ctx, LSMOperationType.FLUSH, true)) {
-            callback.beforeOperation();
-            callback.afterOperation(null, null);
-            callback.afterFinalize(null);
+            callback.afterFinalize(LSMOperationType.FLUSH, null);
             return;
         }
         lsmIndex.scheduleFlush(ctx, callback);
@@ -271,13 +272,12 @@
 
         ILSMComponent newComponent = null;
         try {
-            operation.getCallback().beforeOperation();
             newComponent = lsmIndex.flush(operation);
-            operation.getCallback().afterOperation(null, newComponent);
+            operation.getCallback().afterOperation(LSMOperationType.FLUSH, null, newComponent);
             lsmIndex.markAsValid(newComponent);
         } finally {
             exitComponents(ctx, LSMOperationType.FLUSH, newComponent, false);
-            operation.getCallback().afterFinalize(newComponent);
+            operation.getCallback().afterFinalize(LSMOperationType.FLUSH, newComponent);
         }
         if (LOGGER.isLoggable(Level.INFO)) {
             LOGGER.info("Finished the flush operation for index: " + lsmIndex);
@@ -289,9 +289,7 @@
             throws HyracksDataException, IndexException {
         // Merge should always be a try operation, because it should never fail to enter the components unless the merge policy is erroneous.
         if (!getAndEnterComponents(ctx, LSMOperationType.MERGE, true)) {
-            callback.beforeOperation();
-            callback.afterOperation(null, null);
-            callback.afterFinalize(null);
+            callback.afterFinalize(LSMOperationType.MERGE, null);
             return;
         }
         lsmIndex.scheduleMerge(ctx, callback);
@@ -306,13 +304,12 @@
 
         ILSMComponent newComponent = null;
         try {
-            operation.getCallback().beforeOperation();
             newComponent = lsmIndex.merge(operation);
-            operation.getCallback().afterOperation(ctx.getComponentHolder(), newComponent);
+            operation.getCallback().afterOperation(LSMOperationType.MERGE, ctx.getComponentHolder(), newComponent);
             lsmIndex.markAsValid(newComponent);
         } finally {
             exitComponents(ctx, LSMOperationType.MERGE, newComponent, false);
-            operation.getCallback().afterFinalize(newComponent);
+            operation.getCallback().afterFinalize(LSMOperationType.MERGE, newComponent);
         }
         if (LOGGER.isLoggable(Level.INFO)) {
             LOGGER.info("Finished the merge operation for index: " + lsmIndex);
diff --git a/hyracks/hyracks-storage-am-lsm-common/src/main/java/edu/uci/ics/hyracks/storage/am/lsm/common/impls/NoOpIOOperationCallback.java b/hyracks/hyracks-storage-am-lsm-common/src/main/java/edu/uci/ics/hyracks/storage/am/lsm/common/impls/NoOpIOOperationCallback.java
index e962265..2c8369e 100644
--- a/hyracks/hyracks-storage-am-lsm-common/src/main/java/edu/uci/ics/hyracks/storage/am/lsm/common/impls/NoOpIOOperationCallback.java
+++ b/hyracks/hyracks-storage-am-lsm-common/src/main/java/edu/uci/ics/hyracks/storage/am/lsm/common/impls/NoOpIOOperationCallback.java
@@ -27,18 +27,18 @@
     INSTANCE;
 
     @Override
-    public void beforeOperation() throws HyracksDataException {
+    public void beforeOperation(LSMOperationType opType) throws HyracksDataException {
         // Do nothing.
     }
 
     @Override
-    public void afterOperation(List<ILSMComponent> oldComponents, ILSMComponent newComponent)
+    public void afterOperation(LSMOperationType opType, List<ILSMComponent> oldComponents, ILSMComponent newComponent)
             throws HyracksDataException {
         // Do nothing.
     }
 
     @Override
-    public void afterFinalize(ILSMComponent newComponent) throws HyracksDataException {
+    public void afterFinalize(LSMOperationType opType, ILSMComponent newComponent) throws HyracksDataException {
         // Do nothing.
     }
 
@@ -51,4 +51,9 @@
     public ILSMIOOperationCallback createIOOperationCallback() {
         return INSTANCE;
     }
+
+    @Override
+    public void setNumOfMutableComponents(int count) {
+        // Do nothing.
+    }
 }