diff --git a/source/libs/index/inc/index_fst_util.h b/source/libs/index/inc/index_fst_util.h
index 4af885816f..24b2508678 100644
--- a/source/libs/index/inc/index_fst_util.h
+++ b/source/libs/index/inc/index_fst_util.h
@@ -93,6 +93,28 @@ uint8_t *fstSliceData(FstSlice *s, int32_t *sz);
 
 #define FST_SLICE_LEN(s) (s->end - s->start + 1)
 
+//// stack 
+//
+//typedef (*StackFreeElemFn)(void *elem);
+//
+//typedef struct FstStack {
+//  void   *first;    
+//  void   *end;  
+//  size_t elemSize; 
+//  size_t nElem;
+//  StackFreeElemFn fn;
+//} FstStack;
+//
+//
+//FstStack* fstStackCreate(size_t elemSize, stackFreeElem); 
+//void  *fstStackPush(FstStack *s, void *elem);
+//void  *fstStackTop(FstStack *s);
+//size_t fstStackLen(FstStack *s); 
+//void  fstStackDestory(FstStack *); 
+//
+
+
+  
 #ifdef __cplusplus
 }
 #endif
diff --git a/source/libs/index/src/index_fst.c b/source/libs/index/src/index_fst.c
index 418d1f2bda..4f6a5a236e 100644
--- a/source/libs/index/src/index_fst.c
+++ b/source/libs/index/src/index_fst.c
@@ -40,6 +40,7 @@ void unFinishedNodeDestroyElem(void* elem) {
   FstBuilderNodeUnfinished *b = (FstBuilderNodeUnfinished*)elem;
   fstBuilderNodeDestroy(b->node); 
   free(b->last); 
+  b->last = NULL;
 }  
 void fstUnFinishedNodesDestroy(FstUnFinishedNodes *nodes) {
   if (nodes == NULL) { return; } 
@@ -62,15 +63,15 @@ FstBuilderNode *fstUnFinishedNodesPopRoot(FstUnFinishedNodes *nodes) {
   assert(taosArrayGetSize(nodes->stack) == 1);
 
   FstBuilderNodeUnfinished *un = taosArrayPop(nodes->stack);
-  //assert(un->last == NULL); 
+  assert(un->last == NULL); 
   return un->node;  
 }
 
 FstBuilderNode *fstUnFinishedNodesPopFreeze(FstUnFinishedNodes *nodes, CompiledAddr addr) {
   FstBuilderNodeUnfinished *un = taosArrayPop(nodes->stack);
   fstBuilderNodeUnfinishedLastCompiled(un, addr);
-  free(un->last); // TODO add func FstLastTransitionFree()
-  un->last = NULL;
+  //free(un->last); // TODO add func FstLastTransitionFree()
+  //un->last = NULL;
   return un->node; 
 }
 
@@ -937,9 +938,10 @@ void fstLastTransitionDestroy(FstLastTransition *trn) {
 void fstBuilderNodeUnfinishedLastCompiled(FstBuilderNodeUnfinished *unNode, CompiledAddr addr) {
   FstLastTransition *trn = unNode->last;       
   if (trn == NULL) { return; }  
-
   FstTransition t = {.inp = trn->inp, .out = trn->out, .addr = addr};      
   taosArrayPush(unNode->node->trans, &t); 
+  fstLastTransitionDestroy(trn); 
+  unNode->last = NULL;
   return;
 }
 
diff --git a/source/libs/index/src/index_fst_util.c b/source/libs/index/src/index_fst_util.c
index 532b0b8ac3..ab74a76eb9 100644
--- a/source/libs/index/src/index_fst_util.c
+++ b/source/libs/index/src/index_fst_util.c
@@ -174,5 +174,18 @@ int fstSliceCompare(FstSlice *a, FstSlice *b) {
   else { return 0; } 
 } 
 
+//FstStack* fstStackCreate(size_t elemSize, StackFreeElem freeFn) {
+//  FstStack *s = calloc(1, sizeof(FstStack));
+//  if (s == NULL) { return NULL; }
+//  s-> 
+//  s->freeFn 
+//  
+//}
+//void  *fstStackPush(FstStack *s, void *elem);
+//void  *fstStackTop(FstStack *s);
+//size_t fstStackLen(FstStack *s); 
+//void  *fstStackGetAt(FstStack *s, size_t i);
+//void   fstStackDestory(FstStack *); 
+
 
 
diff --git a/source/libs/index/test/indexTests.cpp b/source/libs/index/test/indexTests.cpp
index 14ff2caf12..a575fb3878 100644
--- a/source/libs/index/test/indexTests.cpp
+++ b/source/libs/index/test/indexTests.cpp
@@ -63,19 +63,26 @@
 //}
 
 int main(int argc, char** argv) {
-  std::string str("abc");
-  FstSlice key = fstSliceCreate((uint8_t *)str.c_str(), str.size());
-  Output   val = 1;
+  FstBuilder *b = fstBuilderCreate(NULL, 1);
+  {
+    std::string str("abc");
+    FstSlice key = fstSliceCreate((uint8_t *)str.c_str(), str.size());
+    Output   val = 1;
+    fstBuilderInsert(b, key, val); 
+  }
 
   //std::string str1("bcd");
   //FstSlice key1 = fstSliceCreate((uint8_t *)str1.c_str(), str1.size());
   //Output   val2 = 10;
-  FstBuilder *b = fstBuilderCreate(NULL, 1);
-  fstBuilderInsert(b, key, val); 
+  {
+    std::string str("bcd");
+    FstSlice key = fstSliceCreate((uint8_t *)str.c_str(), str.size());
+    Output   val = 1;
+    fstBuilderInsert(b, key, val); 
+  } 
   //fstBuilderInsert(b, key1, val2); 
   fstBuilderFinish(b);
   fstBuilderDestroy(b);
-  fstSliceDestroy(&key);
   return 1;
 }