diff --git a/asterix-common/src/main/java/edu/uci/ics/asterix/common/context/AsterixAppRuntimeContext.java b/asterix-common/src/main/java/edu/uci/ics/asterix/common/context/AsterixAppRuntimeContext.java
index 53e0114..1a69a9b 100644
--- a/asterix-common/src/main/java/edu/uci/ics/asterix/common/context/AsterixAppRuntimeContext.java
+++ b/asterix-common/src/main/java/edu/uci/ics/asterix/common/context/AsterixAppRuntimeContext.java
@@ -14,7 +14,7 @@
 import edu.uci.ics.hyracks.storage.am.lsm.common.api.ILSMMergePolicy;
 import edu.uci.ics.hyracks.storage.am.lsm.common.api.ILSMOperationTrackerFactory;
 import edu.uci.ics.hyracks.storage.am.lsm.common.impls.ConstantMergePolicy;
-import edu.uci.ics.hyracks.storage.am.lsm.common.impls.RefCountingOperationTrackerFactory;
+import edu.uci.ics.hyracks.storage.am.lsm.common.impls.ThreadCountingOperationTrackerFactory;
 import edu.uci.ics.hyracks.storage.am.lsm.common.impls.SynchronousScheduler;
 import edu.uci.ics.hyracks.storage.common.buffercache.BufferCache;
 import edu.uci.ics.hyracks.storage.common.buffercache.ClockPageReplacementStrategy;
@@ -65,7 +65,7 @@
 
         lsmIOScheduler = SynchronousScheduler.INSTANCE;
         mergePolicy = new ConstantMergePolicy(3);
-        opTrackerFactory = RefCountingOperationTrackerFactory.INSTANCE;
+        opTrackerFactory = ThreadCountingOperationTrackerFactory.INSTANCE;
 
         ILocalResourceRepositoryFactory persistentLocalResourceRepositoryFactory = new PersistentLocalResourceRepositoryFactory(
                 ioMgr);
diff --git a/asterix-transactions/src/main/java/edu/uci/ics/asterix/transaction/management/ioopcallbacks/LSMBTreeIOOperationCallback.java b/asterix-transactions/src/main/java/edu/uci/ics/asterix/transaction/management/ioopcallbacks/LSMBTreeIOOperationCallback.java
index 434e6ef..10e3805 100644
--- a/asterix-transactions/src/main/java/edu/uci/ics/asterix/transaction/management/ioopcallbacks/LSMBTreeIOOperationCallback.java
+++ b/asterix-transactions/src/main/java/edu/uci/ics/asterix/transaction/management/ioopcallbacks/LSMBTreeIOOperationCallback.java
@@ -20,7 +20,7 @@
 import edu.uci.ics.asterix.transaction.management.opcallbacks.IndexOperationTracker;
 import edu.uci.ics.hyracks.api.exceptions.HyracksDataException;
 import edu.uci.ics.hyracks.storage.am.btree.impls.BTree;
-import edu.uci.ics.hyracks.storage.am.lsm.btree.impls.LSMBTreeComponent;
+import edu.uci.ics.hyracks.storage.am.lsm.btree.impls.LSMBTreeImmutableComponent;
 import edu.uci.ics.hyracks.storage.am.lsm.common.api.ILSMComponent;
 import edu.uci.ics.hyracks.storage.am.lsm.common.api.ILSMIOOperation;
 
@@ -33,7 +33,7 @@
     @Override
     public void afterOperation(ILSMIOOperation operation, List<ILSMComponent> oldComponents, ILSMComponent newComponent)
             throws HyracksDataException {
-        LSMBTreeComponent btreeComponent = (LSMBTreeComponent) newComponent;
+        LSMBTreeImmutableComponent btreeComponent = (LSMBTreeImmutableComponent) newComponent;
         putLSNIntoMetadata(btreeComponent.getBTree(), oldComponents);
     }
 
@@ -45,8 +45,8 @@
         }
         // Get max LSN from the oldComponents. Implies a merge IO operation.
         long maxLSN = -1;
-        for (Object o : oldComponents) {
-            BTree btree = (BTree) o;
+        for (ILSMComponent c : oldComponents) {
+            BTree btree = ((LSMBTreeImmutableComponent) c).getBTree();
             maxLSN = Math.max(getTreeIndexLSN(btree), maxLSN);
         }
         return maxLSN;
diff --git a/asterix-transactions/src/main/java/edu/uci/ics/asterix/transaction/management/ioopcallbacks/LSMInvertedIndexIOOperationCallback.java b/asterix-transactions/src/main/java/edu/uci/ics/asterix/transaction/management/ioopcallbacks/LSMInvertedIndexIOOperationCallback.java
index b1450c1..53cdfd1 100644
--- a/asterix-transactions/src/main/java/edu/uci/ics/asterix/transaction/management/ioopcallbacks/LSMInvertedIndexIOOperationCallback.java
+++ b/asterix-transactions/src/main/java/edu/uci/ics/asterix/transaction/management/ioopcallbacks/LSMInvertedIndexIOOperationCallback.java
@@ -21,7 +21,7 @@
 import edu.uci.ics.hyracks.api.exceptions.HyracksDataException;
 import edu.uci.ics.hyracks.storage.am.lsm.common.api.ILSMComponent;
 import edu.uci.ics.hyracks.storage.am.lsm.common.api.ILSMIOOperation;
-import edu.uci.ics.hyracks.storage.am.lsm.invertedindex.impls.LSMInvertedIndexComponent;
+import edu.uci.ics.hyracks.storage.am.lsm.invertedindex.impls.LSMInvertedIndexImmutableComponent;
 
 public class LSMInvertedIndexIOOperationCallback extends AbstractLSMIOOperationCallback {
 
@@ -32,7 +32,7 @@
     @Override
     public void afterOperation(ILSMIOOperation operation, List<ILSMComponent> oldComponents, ILSMComponent newComponent)
             throws HyracksDataException {
-        LSMInvertedIndexComponent invIndexComponent = (LSMInvertedIndexComponent) newComponent;
+        LSMInvertedIndexImmutableComponent invIndexComponent = (LSMInvertedIndexImmutableComponent) newComponent;
         putLSNIntoMetadata(invIndexComponent.getDeletedKeysBTree(), oldComponents);
     }
 
@@ -45,7 +45,7 @@
         // Get max LSN from the oldComponents. Implies a merge IO operation.
         long maxLSN = -1;
         for (Object o : oldComponents) {
-            LSMInvertedIndexComponent invIndexComponent = (LSMInvertedIndexComponent) o;
+            LSMInvertedIndexImmutableComponent invIndexComponent = (LSMInvertedIndexImmutableComponent) o;
             maxLSN = Math.max(getTreeIndexLSN(invIndexComponent.getDeletedKeysBTree()), maxLSN);
         }
         return maxLSN;
diff --git a/asterix-transactions/src/main/java/edu/uci/ics/asterix/transaction/management/ioopcallbacks/LSMRTreeIOOperationCallback.java b/asterix-transactions/src/main/java/edu/uci/ics/asterix/transaction/management/ioopcallbacks/LSMRTreeIOOperationCallback.java
index ab3c9a6..62da7e7 100644
--- a/asterix-transactions/src/main/java/edu/uci/ics/asterix/transaction/management/ioopcallbacks/LSMRTreeIOOperationCallback.java
+++ b/asterix-transactions/src/main/java/edu/uci/ics/asterix/transaction/management/ioopcallbacks/LSMRTreeIOOperationCallback.java
@@ -21,7 +21,7 @@
 import edu.uci.ics.hyracks.api.exceptions.HyracksDataException;
 import edu.uci.ics.hyracks.storage.am.lsm.common.api.ILSMComponent;
 import edu.uci.ics.hyracks.storage.am.lsm.common.api.ILSMIOOperation;
-import edu.uci.ics.hyracks.storage.am.lsm.rtree.impls.LSMRTreeComponent;
+import edu.uci.ics.hyracks.storage.am.lsm.rtree.impls.LSMRTreeImmutableComponent;
 
 public class LSMRTreeIOOperationCallback extends AbstractLSMIOOperationCallback {
 
@@ -30,8 +30,9 @@
     }
 
     @Override
-    public void afterOperation(ILSMIOOperation operation, List<ILSMComponent> oldComponents, ILSMComponent newComponent) throws HyracksDataException {
-        LSMRTreeComponent rtreeComponent = (LSMRTreeComponent) newComponent;
+    public void afterOperation(ILSMIOOperation operation, List<ILSMComponent> oldComponents, ILSMComponent newComponent)
+            throws HyracksDataException {
+        LSMRTreeImmutableComponent rtreeComponent = (LSMRTreeImmutableComponent) newComponent;
         putLSNIntoMetadata(rtreeComponent.getRTree(), oldComponents);
         putLSNIntoMetadata(rtreeComponent.getBTree(), oldComponents);
     }
@@ -45,7 +46,7 @@
         // Get max LSN from the oldComponents. Implies a merge IO operation.
         long maxLSN = -1;
         for (Object o : oldComponents) {
-            LSMRTreeComponent rtreeComponent = (LSMRTreeComponent) o;
+            LSMRTreeImmutableComponent rtreeComponent = (LSMRTreeImmutableComponent) o;
             maxLSN = Math.max(getTreeIndexLSN(rtreeComponent.getRTree()), maxLSN);
         }
         return maxLSN;
diff --git a/asterix-transactions/src/main/java/edu/uci/ics/asterix/transaction/management/opcallbacks/IndexOperationTracker.java b/asterix-transactions/src/main/java/edu/uci/ics/asterix/transaction/management/opcallbacks/IndexOperationTracker.java
index 04b28be..447c3d2 100644
--- a/asterix-transactions/src/main/java/edu/uci/ics/asterix/transaction/management/opcallbacks/IndexOperationTracker.java
+++ b/asterix-transactions/src/main/java/edu/uci/ics/asterix/transaction/management/opcallbacks/IndexOperationTracker.java
@@ -24,6 +24,7 @@
 import edu.uci.ics.hyracks.storage.am.lsm.common.api.ILSMIndex;
 import edu.uci.ics.hyracks.storage.am.lsm.common.api.ILSMIndexAccessor;
 import edu.uci.ics.hyracks.storage.am.lsm.common.api.ILSMOperationTracker;
+import edu.uci.ics.hyracks.storage.am.lsm.common.impls.LSMOperationType;
 
 public class IndexOperationTracker implements ILSMOperationTracker {
 
@@ -47,21 +48,8 @@
     }
 
     @Override
-    public synchronized boolean beforeOperation(ISearchOperationCallback searchCallback,
-            IModificationOperationCallback modificationCallback, boolean tryOperation) throws HyracksDataException {
-        // Wait for pending flushes to complete.
-        // If flushFlag is set, then the flush is queued to occur by the last completing operation.
-        // This operation should wait for that flush to occur before proceeding.
-        if (index.getFlushStatus(index)) {
-            if (tryOperation) {
-                return false;
-            }
-            try {
-                this.wait();
-            } catch (InterruptedException e) {
-                throw new HyracksDataException(e);
-            }
-        }
+    public void beforeOperation(LSMOperationType opType, ISearchOperationCallback searchCallback,
+            IModificationOperationCallback modificationCallback) throws HyracksDataException {
         numActiveOperations++;
 
         // Increment transactor-local active operations count.
@@ -69,20 +57,19 @@
         if (opCallback != null) {
             opCallback.incrementLocalNumActiveOperations();
         }
-        return true;
     }
 
     @Override
-    public void afterOperation(ISearchOperationCallback searchCallback,
+    public void afterOperation(LSMOperationType opType, ISearchOperationCallback searchCallback,
             IModificationOperationCallback modificationCallback) throws HyracksDataException {
         // Searches are immediately considered complete, because they should not prevent the execution of flushes.
         if (searchCallback != null) {
-            completeOperation(searchCallback, modificationCallback);
+            completeOperation(opType, searchCallback, modificationCallback);
         }
     }
 
     @Override
-    public synchronized void completeOperation(ISearchOperationCallback searchCallback,
+    public void completeOperation(LSMOperationType opType, ISearchOperationCallback searchCallback,
             IModificationOperationCallback modificationCallback) throws HyracksDataException {
         numActiveOperations--;
 
@@ -93,7 +80,7 @@
         }
         // If we need a flush, and this is the last completing operation, then schedule the flush.
         // Once the flush has completed notify all waiting operations.
-        if (index.getFlushStatus(index) && numActiveOperations == 0) {
+        if (index.getFlushStatus(index) && numActiveOperations == 0 && opType != LSMOperationType.FLUSH) {
             if (accessor == null) {
                 accessor = (ILSMIndexAccessor) index.createAccessor(NoOpOperationCallback.INSTANCE,
                         NoOpOperationCallback.INSTANCE);
diff --git a/asterix-transactions/src/main/java/edu/uci/ics/asterix/transaction/management/service/transaction/TransactionContext.java b/asterix-transactions/src/main/java/edu/uci/ics/asterix/transaction/management/service/transaction/TransactionContext.java
index a88ed5f..67e280a 100644
--- a/asterix-transactions/src/main/java/edu/uci/ics/asterix/transaction/management/service/transaction/TransactionContext.java
+++ b/asterix-transactions/src/main/java/edu/uci/ics/asterix/transaction/management/service/transaction/TransactionContext.java
@@ -30,6 +30,7 @@
 import edu.uci.ics.hyracks.api.exceptions.HyracksDataException;
 import edu.uci.ics.hyracks.storage.am.common.api.IModificationOperationCallback;
 import edu.uci.ics.hyracks.storage.am.lsm.common.api.ILSMIndex;
+import edu.uci.ics.hyracks.storage.am.lsm.common.impls.LSMOperationType;
 
 /**
  * Represents a holder object that contains all information related to a
@@ -54,7 +55,7 @@
     private TransactionSubsystem transactionSubsystem;
     private LogicalLogLocator firstLogLocator;//firstLSN of the Job
     private LogicalLogLocator lastLogLocator;//lastLSN of the Job
-    private TransactionState txnState; 
+    private TransactionState txnState;
     private long startWaitTime;
     private int status;
     private Set<ICloseable> resources = new HashSet<ICloseable>();
@@ -102,7 +103,8 @@
             for (int i = 0; i < indexes.size(); i++) {
                 ILSMIndex index = indexes.get(i);
                 IModificationOperationCallback modificationCallback = (IModificationOperationCallback) callbacks.get(i);
-                ((IndexOperationTracker) index.getOperationTracker()).completeOperation(null, modificationCallback);
+                ((IndexOperationTracker) index.getOperationTracker()).completeOperation(LSMOperationType.MODIFICATION,
+                        null, modificationCallback);
             }
         }
     }
@@ -122,7 +124,7 @@
     public LogicalLogLocator getFirstLogLocator() {
         return firstLogLocator;
     }
-    
+
     public LogicalLogLocator getLastLogLocator() {
         return lastLogLocator;
     }