diff --git a/hyracks-storage-am-btree/src/main/java/edu/uci/ics/hyracks/storage/am/btree/frames/BTreeNSMInteriorFrame.java b/hyracks-storage-am-btree/src/main/java/edu/uci/ics/hyracks/storage/am/btree/frames/BTreeNSMInteriorFrame.java
index 728e5d7..09aadb8 100644
--- a/hyracks-storage-am-btree/src/main/java/edu/uci/ics/hyracks/storage/am/btree/frames/BTreeNSMInteriorFrame.java
+++ b/hyracks-storage-am-btree/src/main/java/edu/uci/ics/hyracks/storage/am/btree/frames/BTreeNSMInteriorFrame.java
@@ -52,10 +52,6 @@
         cmpFrameTuple = tupleWriter.createTupleReference();
     }
 
-    private int getLeftChildPageOff(ITupleReference tuple) {
-        return tuple.getFieldStart(tuple.getFieldCount() - 1) + tuple.getFieldLength(tuple.getFieldCount() - 1);
-    }
-
     @Override
     public void initBuffer(byte level) {
         super.initBuffer(level);
@@ -64,15 +60,15 @@
 
     @Override
     public FrameOpSpaceStatus hasSpaceInsert(ITupleReference tuple) {
-        int bytesRequired = tupleWriter.bytesRequired(tuple) + 8; // for the two
-        // childpointers
-        if (bytesRequired + slotManager.getSlotSize() <= buf.capacity() - buf.getInt(freeSpaceOff)
-                - (buf.getInt(tupleCountOff) * slotManager.getSlotSize()))
+    	// Tuple bytes + child pointer + slot.
+    	int bytesRequired = tupleWriter.bytesRequired(tuple) + childPtrSize + slotManager.getSlotSize();
+        if (bytesRequired <= getFreeContiguousSpace()) {
             return FrameOpSpaceStatus.SUFFICIENT_CONTIGUOUS_SPACE;
-        else if (bytesRequired + slotManager.getSlotSize() <= buf.getInt(totalFreeSpaceOff))
+        }
+        if (bytesRequired <= getTotalFreeSpace()) {
             return FrameOpSpaceStatus.SUFFICIENT_SPACE;
-        else
-            return FrameOpSpaceStatus.INSUFFICIENT_SPACE;
+        }
+        return FrameOpSpaceStatus.INSUFFICIENT_SPACE;
     }
 
     @Override
@@ -89,7 +85,6 @@
     
     @Override
     public int findUpdateTupleIndex(ITupleReference tuple, MultiComparator cmp) throws TreeIndexException {
-        // TODO: Maybe craft the interface such that this is not possible?
         throw new UnsupportedOperationException("Cannot update tuples in interior node.");
     }
 
@@ -148,7 +143,7 @@
 
         int tuplesToLeft = (tupleCount / 2) + (tupleCount % 2);
         ITreeIndexFrame targetFrame = null;
-        frameTuple.resetByTupleOffset(buf, getTupleOffset(tuplesToLeft - 1));
+        frameTuple.resetByTupleIndex(this, tuplesToLeft - 1);
         if (cmp.compare(tuple, frameTuple) <= 0) {
             targetFrame = this;
         } else {
@@ -437,6 +432,10 @@
         return rightLeafOff;
     }
     
+    private int getLeftChildPageOff(ITupleReference tuple) {
+        return tuple.getFieldStart(tuple.getFieldCount() - 1) + tuple.getFieldLength(tuple.getFieldCount() - 1);
+    }
+    
     // TODO: can we put these into a common AbstractFrame or something?
     @Override
     public boolean getSmFlag() {
diff --git a/hyracks-storage-am-btree/src/main/java/edu/uci/ics/hyracks/storage/am/btree/impls/BTree.java b/hyracks-storage-am-btree/src/main/java/edu/uci/ics/hyracks/storage/am/btree/impls/BTree.java
index 7eff304..2895686 100644
--- a/hyracks-storage-am-btree/src/main/java/edu/uci/ics/hyracks/storage/am/btree/impls/BTree.java
+++ b/hyracks-storage-am-btree/src/main/java/edu/uci/ics/hyracks/storage/am/btree/impls/BTree.java
@@ -900,8 +900,7 @@
             BTreeSplitKey copyKey = ctx.splitKey.duplicate(ctx.leafFrame.getTupleWriter().createTupleReference());
             tuple = copyKey.getTuple();
 
-            frontier.lastTuple.resetByTupleOffset(frontier.page.getBuffer(),
-                    ctx.interiorFrame.getTupleOffset(ctx.interiorFrame.getTupleCount() - 1));
+            frontier.lastTuple.resetByTupleIndex(ctx.interiorFrame, ctx.interiorFrame.getTupleCount() - 1);
             int splitKeySize = ctx.tupleWriter.bytesRequired(frontier.lastTuple, 0, cmp.getKeyFieldCount());
             ctx.splitKey.initData(splitKeySize);
             ctx.tupleWriter
diff --git a/hyracks-storage-am-common/src/main/java/edu/uci/ics/hyracks/storage/am/common/api/ITreeIndex.java b/hyracks-storage-am-common/src/main/java/edu/uci/ics/hyracks/storage/am/common/api/ITreeIndex.java
index d4e1703..6fe5219 100644
--- a/hyracks-storage-am-common/src/main/java/edu/uci/ics/hyracks/storage/am/common/api/ITreeIndex.java
+++ b/hyracks-storage-am-common/src/main/java/edu/uci/ics/hyracks/storage/am/common/api/ITreeIndex.java
@@ -19,6 +19,11 @@
 import edu.uci.ics.hyracks.dataflow.common.data.accessors.ITupleReference;
 import edu.uci.ics.hyracks.storage.am.common.ophelpers.IndexOp;
 
+/**
+ * Interface implemented by tree-based index structures, describing their
+ * supported operations. Indexes implementing this interface can easily reuse
+ * the tree index operators for dataflow.
+ */
 public interface ITreeIndex {
 	// init:
 
@@ -66,12 +71,12 @@
 
 	public IFreePageManager getFreePageManager();
 
-	public int getRootPageId();
-
 	public ITreeIndexFrameFactory getLeafFrameFactory();
 
 	public ITreeIndexFrameFactory getInteriorFrameFactory();
 
+	public int getRootPageId();
+	
 	public int getFieldCount();
 
 	public IndexType getIndexType();
diff --git a/hyracks-storage-am-common/src/main/java/edu/uci/ics/hyracks/storage/am/common/api/ITreeIndexFrame.java b/hyracks-storage-am-common/src/main/java/edu/uci/ics/hyracks/storage/am/common/api/ITreeIndexFrame.java
index fb32fab..01ea75f 100644
--- a/hyracks-storage-am-common/src/main/java/edu/uci/ics/hyracks/storage/am/common/api/ITreeIndexFrame.java
+++ b/hyracks-storage-am-common/src/main/java/edu/uci/ics/hyracks/storage/am/common/api/ITreeIndexFrame.java
@@ -26,6 +26,8 @@
 
 public interface ITreeIndexFrame {
 
+	public void initBuffer(byte level);
+	
     public FrameOpSpaceStatus hasSpaceInsert(ITupleReference tuple);
 	
 	public void insert(ITupleReference tuple, int tupleIndex);    
@@ -39,10 +41,9 @@
     // returns true if slots were modified, false otherwise
     public boolean compact();
 
+    // returns true if compressed.
     public boolean compress() throws HyracksDataException;
 
-    public void initBuffer(byte level);
-
     public int getTupleCount();
 
     public int getTupleOffset(int slotNum);
diff --git a/hyracks-storage-am-common/src/main/java/edu/uci/ics/hyracks/storage/am/common/frames/TreeIndexNSMFrame.java b/hyracks-storage-am-common/src/main/java/edu/uci/ics/hyracks/storage/am/common/frames/TreeIndexNSMFrame.java
index 574456e..5e5360a 100644
--- a/hyracks-storage-am-common/src/main/java/edu/uci/ics/hyracks/storage/am/common/frames/TreeIndexNSMFrame.java
+++ b/hyracks-storage-am-common/src/main/java/edu/uci/ics/hyracks/storage/am/common/frames/TreeIndexNSMFrame.java
@@ -309,4 +309,9 @@
     public ITreeIndexTupleReference createTupleReference() {
     	return tupleWriter.createTupleReference();
     }
+    
+	public int getFreeContiguousSpace() {
+		return buf.capacity() - getFreeSpaceOff()
+				- (getTupleCount() * slotManager.getSlotSize());
+	}
 }