diff --git a/include/libs/sync/sync.h b/include/libs/sync/sync.h
index 5ffcbb7a0919f6277414405e03e690f5115f3909..4ac4922e80a0558a77949186f9e3944fe73b2b18 100644
--- a/include/libs/sync/sync.h
+++ b/include/libs/sync/sync.h
@@ -98,8 +98,17 @@ typedef struct SSyncFSM {
 
   void (*FpRestoreFinishCb)(struct SSyncFSM* pFsm);
   int32_t (*FpGetSnapshot)(struct SSyncFSM* pFsm, SSnapshot* pSnapshot);
-  void* (*FpSnapshotRead)(struct SSyncFSM* pFsm, const SSnapshot* snapshot, void* iter, char** ppBuf, int32_t* len);
-  int32_t (*FpSnapshotApply)(struct SSyncFSM* pFsm, const SSnapshot* snapshot, char* pBuf, int32_t len);
+
+  // if (*ppIter == NULL) 
+  //   *ppIter = new iter;
+  // else 
+  //   *ppIter.next();
+  //
+  // if success, return 0. else return error code
+  int32_t (*FpSnapshotRead)(struct SSyncFSM* pFsm, const SSnapshot* pSnapshot, void** ppIter, char** ppBuf, int32_t* len);
+  
+  // apply data into fsm
+  int32_t (*FpSnapshotApply)(struct SSyncFSM* pFsm, const SSnapshot* pSnapshot, char* pBuf, int32_t len);
 
   void (*FpReConfigCb)(struct SSyncFSM* pFsm, SSyncCfg newCfg, SReConfigCbMeta cbMeta);
 
diff --git a/source/dnode/mnode/impl/src/mndSync.c b/source/dnode/mnode/impl/src/mndSync.c
index 2b4b472c35007f91dc82fb01dd1c8a3a76bdc53d..0ddb542b382bae5cb2242773b4d177a554bab814 100644
--- a/source/dnode/mnode/impl/src/mndSync.c
+++ b/source/dnode/mnode/impl/src/mndSync.c
@@ -55,7 +55,7 @@ void mndRestoreFinish(struct SSyncFSM *pFsm) {
   pMnode->syncMgmt.restored = true;
 }
 
-void* mndSnapshotRead(struct SSyncFSM* pFsm, const SSnapshot* snapshot, void* iter, char** ppBuf, int32_t* len) {
+int32_t mndSnapshotRead(struct SSyncFSM* pFsm, const SSnapshot* pSnapshot, void** ppIter, char** ppBuf, int32_t* len) {
   /*
   SMnode *pMnode = pFsm->data;
   SSdbIter *pIter;
@@ -68,10 +68,10 @@ void* mndSnapshotRead(struct SSyncFSM* pFsm, const SSnapshot* snapshot, void* it
   return pIter;
   */
 
-  return NULL;
+  return 0;
 }
 
-int32_t mndSnapshotApply(struct SSyncFSM* pFsm, const SSnapshot* snapshot, char* pBuf, int32_t len) {
+int32_t mndSnapshotApply(struct SSyncFSM* pFsm, const SSnapshot* pSnapshot, char* pBuf, int32_t len) {
   SMnode *pMnode = pFsm->data;
   sdbWrite(pMnode->pSdb, (SSdbRaw*)pBuf);
   return 0;