diff --git a/include/libs/wal/wal.h b/include/libs/wal/wal.h
index 907b3be5609b119f7a7b9d48c68d88d1bc53f38c..220c4f73e0867b9ca71ef4adb2a3c9d5ac9ffa21 100644
--- a/include/libs/wal/wal.h
+++ b/include/libs/wal/wal.h
@@ -114,21 +114,30 @@ typedef struct SWal {
   int64_t       refId;
   TdThreadMutex mutex;
   // ref
-  SHashObj *pRefHash;  // ref -> SWalRef
+  SHashObj *pRefHash;  // refId -> SWalRef
   // path
   char path[WAL_PATH_LEN];
   // reusable write head
   SWalCkHead writeHead;
-} SWal;  // WAL HANDLE
+} SWal;
+
+typedef struct {
+  int64_t refId;
+  int64_t refVer;
+  int64_t refFile;
+  SWal   *pWal;
+} SWalRef;
 
 typedef struct {
   int8_t scanUncommited;
+  int8_t scanNotApplied;
   int8_t scanMeta;
   int8_t enableRef;
 } SWalFilterCond;
 
 typedef struct {
   SWal          *pWal;
+  int64_t        readerId;
   TdFilePtr      pLogFile;
   TdFilePtr      pIdxFile;
   int64_t        curFileFirstVer;
@@ -138,7 +147,8 @@ typedef struct {
   int8_t         curStopped;
   TdThreadMutex  mutex;
   SWalFilterCond cond;
-  SWalCkHead    *pHead;
+  // TODO remove it
+  SWalCkHead *pHead;
 } SWalReader;
 
 // module initialization
@@ -157,11 +167,7 @@ int32_t walWrite(SWal *, int64_t index, tmsg_t msgType, const void *body, int32_
 int32_t walWriteWithSyncInfo(SWal *, int64_t index, tmsg_t msgType, SWalSyncInfo syncMeta, const void *body,
                              int32_t bodyLen);
 
-// This interface assign version automatically and return to caller.
-// When using this interface with concurrent writes,
-// wal will write all logs atomically,
-// but not sure which one will be actually write first,
-// and then the unique index of successful writen is returned.
+// Assign version automatically and return to caller,
 // -1 will be returned for failed writes
 int64_t walAppendLog(SWal *, tmsg_t msgType, SWalSyncInfo syncMeta, const void *body, int32_t bodyLen);
 
@@ -191,17 +197,15 @@ void    walSetReaderCapacity(SWalReader *pRead, int32_t capacity);
 int32_t walFetchHead(SWalReader *pRead, int64_t ver, SWalCkHead *pHead);
 int32_t walFetchBody(SWalReader *pRead, SWalCkHead **ppHead);
 int32_t walSkipFetchBody(SWalReader *pRead, const SWalCkHead *pHead);
-typedef struct {
-  int64_t refId;
-  int64_t ver;
-} SWalRef;
+
+SWalRef *walRefCommittedVer(SWal *);
 
 SWalRef *walOpenRef(SWal *);
-void     walCloseRef(SWalRef *);
+void     walCloseRef(SWal *pWal, int64_t refId);
 int32_t  walRefVer(SWalRef *, int64_t ver);
-int32_t  walUnrefVer(SWal *);
+void     walUnrefVer(SWalRef *);
 
-// help function for raft
+// helper function for raft
 bool walLogExist(SWal *, int64_t ver);
 bool walIsEmpty(SWal *);
 
diff --git a/source/dnode/vnode/src/inc/tq.h b/source/dnode/vnode/src/inc/tq.h
index b063e552f683536736546d7a5e2f7df04ec303ec..262300a3e73f9f4f879f5f1e9e9304ce5b180aef 100644
--- a/source/dnode/vnode/src/inc/tq.h
+++ b/source/dnode/vnode/src/inc/tq.h
@@ -104,6 +104,8 @@ typedef struct {
   // TODO remove
   SWalReader* pWalReader;
 
+  SWalRef* pRef;
+
   // push
   STqPushHandle pushHandle;
 
diff --git a/source/dnode/vnode/src/tq/tq.c b/source/dnode/vnode/src/tq/tq.c
index 8ea4b8d98b5c672b3f9ff3bca341153ce6dd0be6..118e3a5d43d159abf7f3ed8a901c2707e7987cdf 100644
--- a/source/dnode/vnode/src/tq/tq.c
+++ b/source/dnode/vnode/src/tq/tq.c
@@ -212,6 +212,15 @@ int32_t tqProcessOffsetCommitReq(STQ* pTq, char* msg, int32_t msgLen) {
     ASSERT(0);
     return -1;
   }
+
+  if (offset.val.type == TMQ_OFFSET__LOG) {
+    STqHandle* pHandle = taosHashGet(pTq->handles, offset.subKey, strlen(offset.subKey));
+    if (walRefVer(pHandle->pRef, offset.val.version) < 0) {
+      ASSERT(0);
+      return -1;
+    }
+  }
+
   /*}*/
   /*}*/
 
@@ -376,8 +385,8 @@ int32_t tqProcessPollReq(STQ* pTq, SRpcMsg* pMsg) {
   }
 
   if (pHandle->execHandle.subType != TOPIC_SUB_TYPE__COLUMN) {
-    int64_t     fetchVer = fetchOffsetNew.version + 1;
-    SWalCkHead* pCkHead = taosMemoryMalloc(sizeof(SWalCkHead) + 2048);
+    int64_t fetchVer = fetchOffsetNew.version + 1;
+    pCkHead = taosMemoryMalloc(sizeof(SWalCkHead) + 2048);
     if (pCkHead == NULL) {
       code = -1;
       goto OVER;
@@ -534,11 +543,14 @@ int32_t tqProcessVgChangeReq(STQ* pTq, char* msg, int32_t msgLen) {
 
     pHandle->execHandle.subType = req.subType;
     pHandle->fetchMeta = req.withMeta;
+    // TODO version should be assigned and refed during preprocess
+    SWalRef* pRef = walRefCommittedVer(pTq->pVnode->pWal);
+    if (pRef == NULL) {
+      ASSERT(0);
+    }
+    int64_t ver = pRef->refVer;
+    pHandle->pRef = pRef;
 
-    pHandle->pWalReader = walOpenReader(pTq->pVnode->pWal, NULL);
-
-    // TODO version should be assigned in preprocess
-    int64_t ver = walGetCommittedVer(pTq->pVnode->pWal);
     if (pHandle->execHandle.subType == TOPIC_SUB_TYPE__COLUMN) {
       pHandle->execHandle.execCol.qmsg = req.qmsg;
       pHandle->snapshotVer = ver;
@@ -560,10 +572,14 @@ int32_t tqProcessVgChangeReq(STQ* pTq, char* msg, int32_t msgLen) {
       pHandle->execHandle.pExecReader = qExtractReaderFromStreamScanner(scanner);
       ASSERT(pHandle->execHandle.pExecReader);
     } else if (pHandle->execHandle.subType == TOPIC_SUB_TYPE__DB) {
+      pHandle->pWalReader = walOpenReader(pTq->pVnode->pWal, NULL);
+
       pHandle->execHandle.pExecReader = tqOpenReader(pTq->pVnode);
       pHandle->execHandle.execDb.pFilterOutTbUid =
           taosHashInit(64, taosGetDefaultHashFunction(TSDB_DATA_TYPE_BIGINT), false, HASH_NO_LOCK);
     } else if (pHandle->execHandle.subType == TOPIC_SUB_TYPE__TABLE) {
+      pHandle->pWalReader = walOpenReader(pTq->pVnode->pWal, NULL);
+
       pHandle->execHandle.execTb.suid = req.suid;
       SArray* tbUidList = taosArrayInit(0, sizeof(int64_t));
       vnodeGetCtbIdList(pTq->pVnode, req.suid, tbUidList);
diff --git a/source/dnode/vnode/src/tq/tqMeta.c b/source/dnode/vnode/src/tq/tqMeta.c
index 620417016f9fd44e395edf878cc511f44e9ce22b..290ffe5c8d6a16865df7ee1296c871ccebf0a847 100644
--- a/source/dnode/vnode/src/tq/tqMeta.c
+++ b/source/dnode/vnode/src/tq/tqMeta.c
@@ -52,7 +52,7 @@ int32_t tqMetaOpen(STQ* pTq) {
     ASSERT(0);
   }
 
-  TXN txn;
+  TXN txn = {0};
 
   if (tdbTxnOpen(&txn, 0, tdbDefaultMalloc, tdbDefaultFree, NULL, 0) < 0) {
     ASSERT(0);
@@ -75,7 +75,13 @@ int32_t tqMetaOpen(STQ* pTq) {
     STqHandle handle;
     tDecoderInit(&decoder, (uint8_t*)pVal, vLen);
     tDecodeSTqHandle(&decoder, &handle);
-    handle.pWalReader = walOpenReader(pTq->pVnode->pWal, NULL);
+
+    handle.pRef = walOpenRef(pTq->pVnode->pWal);
+    if (handle.pRef == NULL) {
+      ASSERT(0);
+    }
+    walRefVer(handle.pRef, handle.snapshotVer);
+
     if (handle.execHandle.subType == TOPIC_SUB_TYPE__COLUMN) {
       SReadHandle reader = {
           .meta = pTq->pVnode->pMeta,
@@ -94,6 +100,7 @@ int32_t tqMetaOpen(STQ* pTq) {
       handle.execHandle.pExecReader = qExtractReaderFromStreamScanner(scanner);
       ASSERT(handle.execHandle.pExecReader);
     } else {
+      handle.pWalReader = walOpenReader(pTq->pVnode->pWal, NULL);
       handle.execHandle.execDb.pFilterOutTbUid =
           taosHashInit(64, taosGetDefaultHashFunction(TSDB_DATA_TYPE_BIGINT), false, HASH_NO_LOCK);
     }
diff --git a/source/libs/wal/src/walMgmt.c b/source/libs/wal/src/walMgmt.c
index 491b982968d4fdfb75d3c5fe2cc6e4b27d8c2ebf..85238e87b9f5c5549f2a1cf82435dca8fd85b5a4 100644
--- a/source/libs/wal/src/walMgmt.c
+++ b/source/libs/wal/src/walMgmt.c
@@ -93,7 +93,7 @@ SWal *walOpen(const char *path, SWalCfg *pCfg) {
   }
 
   // init ref
-  pWal->pRefHash = taosHashInit(64, taosGetDefaultHashFunction(TSDB_DATA_TYPE_UBIGINT), true, HASH_ENTRY_LOCK);
+  pWal->pRefHash = taosHashInit(64, taosGetDefaultHashFunction(TSDB_DATA_TYPE_BIGINT), true, HASH_ENTRY_LOCK);
   if (pWal->pRefHash == NULL) {
     taosMemoryFree(pWal);
     return NULL;
diff --git a/source/libs/wal/src/walRead.c b/source/libs/wal/src/walRead.c
index 6d0e844e8e2f17681f0aa7559153bbd4e9eeb24c..ac62b7d98dfeec5e7df073ef165a79d1ad95b7f6 100644
--- a/source/libs/wal/src/walRead.c
+++ b/source/libs/wal/src/walRead.c
@@ -21,107 +21,112 @@ static int32_t walFetchBodyNew(SWalReader *pRead);
 static int32_t walSkipFetchBodyNew(SWalReader *pRead);
 
 SWalReader *walOpenReader(SWal *pWal, SWalFilterCond *cond) {
-  SWalReader *pRead = taosMemoryCalloc(1, sizeof(SWalReader));
-  if (pRead == NULL) {
+  SWalReader *pReader = taosMemoryCalloc(1, sizeof(SWalReader));
+  if (pReader == NULL) {
     terrno = TSDB_CODE_OUT_OF_MEMORY;
     return NULL;
   }
 
-  pRead->pWal = pWal;
-  pRead->pIdxFile = NULL;
-  pRead->pLogFile = NULL;
-  pRead->curVersion = -1;
-  pRead->curFileFirstVer = -1;
-  pRead->curInvalid = 1;
-  pRead->capacity = 0;
+  pReader->pWal = pWal;
+  pReader->readerId = tGenIdPI64();
+  pReader->pIdxFile = NULL;
+  pReader->pLogFile = NULL;
+  pReader->curVersion = -1;
+  pReader->curFileFirstVer = -1;
+  pReader->curInvalid = 1;
+  pReader->capacity = 0;
   if (cond) {
-    pRead->cond = *cond;
+    pReader->cond = *cond;
   } else {
-    pRead->cond.scanMeta = 0;
-    pRead->cond.scanUncommited = 0;
-    pRead->cond.enableRef = 0;
+    pReader->cond.scanUncommited = 0;
+    pReader->cond.scanNotApplied = 0;
+    pReader->cond.scanMeta = 0;
+    pReader->cond.enableRef = 0;
   }
 
-  taosThreadMutexInit(&pRead->mutex, NULL);
+  taosThreadMutexInit(&pReader->mutex, NULL);
 
-  /*if (pRead->cond.enableRef) {*/
-  /*walOpenRef(pWal);*/
-  /*}*/
-
-  pRead->pHead = taosMemoryMalloc(sizeof(SWalCkHead));
-  if (pRead->pHead == NULL) {
+  pReader->pHead = taosMemoryMalloc(sizeof(SWalCkHead));
+  if (pReader->pHead == NULL) {
     terrno = TSDB_CODE_WAL_OUT_OF_MEMORY;
-    taosMemoryFree(pRead);
+    taosMemoryFree(pReader);
     return NULL;
   }
 
-  return pRead;
+  /*if (pReader->cond.enableRef) {*/
+  /* taosHashPut(pWal->pRefHash, &pReader->readerId, sizeof(int64_t), &pReader, sizeof(void *));*/
+  /*}*/
+
+  return pReader;
 }
 
-void walCloseReader(SWalReader *pRead) {
-  taosCloseFile(&pRead->pIdxFile);
-  taosCloseFile(&pRead->pLogFile);
-  taosMemoryFreeClear(pRead->pHead);
-  taosMemoryFree(pRead);
+void walCloseReader(SWalReader *pReader) {
+  taosCloseFile(&pReader->pIdxFile);
+  taosCloseFile(&pReader->pLogFile);
+  /*if (pReader->cond.enableRef) {*/
+  /*taosHashRemove(pReader->pWal->pRefHash, &pReader->readerId, sizeof(int64_t));*/
+  /*}*/
+  taosMemoryFreeClear(pReader->pHead);
+  taosMemoryFree(pReader);
 }
 
-int32_t walNextValidMsg(SWalReader *pRead) {
-  int64_t fetchVer = pRead->curVersion;
-  int64_t lastVer = walGetLastVer(pRead->pWal);
-  int64_t committedVer = walGetCommittedVer(pRead->pWal);
-  int64_t appliedVer = walGetAppliedVer(pRead->pWal);
-  int64_t endVer = pRead->cond.scanUncommited ? lastVer : committedVer;
+int32_t walNextValidMsg(SWalReader *pReader) {
+  int64_t fetchVer = pReader->curVersion;
+  int64_t lastVer = walGetLastVer(pReader->pWal);
+  int64_t committedVer = walGetCommittedVer(pReader->pWal);
+  int64_t appliedVer = walGetAppliedVer(pReader->pWal);
+  int64_t endVer = pReader->cond.scanUncommited ? lastVer : committedVer;
   endVer = TMIN(appliedVer, endVer);
 
   wDebug("vgId:%d wal start to fetch, ver %ld, last ver %ld commit ver %ld, applied ver %ld, end ver %ld",
-         pRead->pWal->cfg.vgId, fetchVer, lastVer, committedVer, appliedVer, endVer);
-  pRead->curStopped = 0;
+         pReader->pWal->cfg.vgId, fetchVer, lastVer, committedVer, appliedVer, endVer);
+  pReader->curStopped = 0;
   while (fetchVer <= endVer) {
-    if (walFetchHeadNew(pRead, fetchVer) < 0) {
+    if (walFetchHeadNew(pReader, fetchVer) < 0) {
       return -1;
     }
-    if (pRead->pHead->head.msgType == TDMT_VND_SUBMIT ||
-        (IS_META_MSG(pRead->pHead->head.msgType) && pRead->cond.scanMeta)) {
-      if (walFetchBodyNew(pRead) < 0) {
+    if (pReader->pHead->head.msgType == TDMT_VND_SUBMIT ||
+        (IS_META_MSG(pReader->pHead->head.msgType) && pReader->cond.scanMeta)) {
+      if (walFetchBodyNew(pReader) < 0) {
         return -1;
       }
       return 0;
     } else {
-      if (walSkipFetchBodyNew(pRead) < 0) {
+      if (walSkipFetchBodyNew(pReader) < 0) {
         return -1;
       }
       fetchVer++;
-      ASSERT(fetchVer == pRead->curVersion);
+      ASSERT(fetchVer == pReader->curVersion);
     }
   }
-  pRead->curStopped = 1;
+  pReader->curStopped = 1;
   return -1;
 }
 
-static int64_t walReadSeekFilePos(SWalReader *pRead, int64_t fileFirstVer, int64_t ver) {
+static int64_t walReadSeekFilePos(SWalReader *pReader, int64_t fileFirstVer, int64_t ver) {
   int64_t ret = 0;
 
-  TdFilePtr pIdxTFile = pRead->pIdxFile;
-  TdFilePtr pLogTFile = pRead->pLogFile;
+  TdFilePtr pIdxTFile = pReader->pIdxFile;
+  TdFilePtr pLogTFile = pReader->pLogFile;
 
   // seek position
   int64_t offset = (ver - fileFirstVer) * sizeof(SWalIdxEntry);
   ret = taosLSeekFile(pIdxTFile, offset, SEEK_SET);
   if (ret < 0) {
     terrno = TAOS_SYSTEM_ERROR(errno);
-    wError("vgId:%d, failed to seek idx file, index:%" PRId64 ", pos:%" PRId64 ", since %s", pRead->pWal->cfg.vgId, ver,
-           offset, terrstr());
+    wError("vgId:%d, failed to seek idx file, index:%" PRId64 ", pos:%" PRId64 ", since %s", pReader->pWal->cfg.vgId,
+           ver, offset, terrstr());
     return -1;
   }
   SWalIdxEntry entry = {0};
   if ((ret = taosReadFile(pIdxTFile, &entry, sizeof(SWalIdxEntry))) != sizeof(SWalIdxEntry)) {
     if (ret < 0) {
       terrno = TAOS_SYSTEM_ERROR(errno);
-      wError("vgId:%d, failed to read idx file, since %s", pRead->pWal->cfg.vgId, terrstr());
+      wError("vgId:%d, failed to read idx file, since %s", pReader->pWal->cfg.vgId, terrstr());
     } else {
       terrno = TSDB_CODE_WAL_FILE_CORRUPTED;
       wError("vgId:%d, read idx file incompletely, read bytes %" PRId64 ", bytes should be %" PRIu64,
-             pRead->pWal->cfg.vgId, ret, sizeof(SWalIdxEntry));
+             pReader->pWal->cfg.vgId, ret, sizeof(SWalIdxEntry));
     }
     return -1;
   }
@@ -130,79 +135,79 @@ static int64_t walReadSeekFilePos(SWalReader *pRead, int64_t fileFirstVer, int64
   ret = taosLSeekFile(pLogTFile, entry.offset, SEEK_SET);
   if (ret < 0) {
     terrno = TAOS_SYSTEM_ERROR(errno);
-    wError("vgId:%d, failed to seek log file, index:%" PRId64 ", pos:%" PRId64 ", since %s", pRead->pWal->cfg.vgId, ver,
-           entry.offset, terrstr());
+    wError("vgId:%d, failed to seek log file, index:%" PRId64 ", pos:%" PRId64 ", since %s", pReader->pWal->cfg.vgId,
+           ver, entry.offset, terrstr());
     return -1;
   }
   return ret;
 }
 
-static int32_t walReadChangeFile(SWalReader *pRead, int64_t fileFirstVer) {
+static int32_t walReadChangeFile(SWalReader *pReader, int64_t fileFirstVer) {
   char fnameStr[WAL_FILE_LEN];
 
-  taosCloseFile(&pRead->pIdxFile);
-  taosCloseFile(&pRead->pLogFile);
+  taosCloseFile(&pReader->pIdxFile);
+  taosCloseFile(&pReader->pLogFile);
 
-  walBuildLogName(pRead->pWal, fileFirstVer, fnameStr);
-  TdFilePtr pLogTFile = taosOpenFile(fnameStr, TD_FILE_READ);
-  if (pLogTFile == NULL) {
+  walBuildLogName(pReader->pWal, fileFirstVer, fnameStr);
+  TdFilePtr pLogFile = taosOpenFile(fnameStr, TD_FILE_READ);
+  if (pLogFile == NULL) {
     terrno = TAOS_SYSTEM_ERROR(errno);
-    wError("vgId:%d, cannot open file %s, since %s", pRead->pWal->cfg.vgId, fnameStr, terrstr());
+    wError("vgId:%d, cannot open file %s, since %s", pReader->pWal->cfg.vgId, fnameStr, terrstr());
     return -1;
   }
 
-  pRead->pLogFile = pLogTFile;
+  pReader->pLogFile = pLogFile;
 
-  walBuildIdxName(pRead->pWal, fileFirstVer, fnameStr);
-  TdFilePtr pIdxTFile = taosOpenFile(fnameStr, TD_FILE_READ);
-  if (pIdxTFile == NULL) {
+  walBuildIdxName(pReader->pWal, fileFirstVer, fnameStr);
+  TdFilePtr pIdxFile = taosOpenFile(fnameStr, TD_FILE_READ);
+  if (pIdxFile == NULL) {
     terrno = TAOS_SYSTEM_ERROR(errno);
-    wError("vgId:%d, cannot open file %s, since %s", pRead->pWal->cfg.vgId, fnameStr, terrstr());
+    wError("vgId:%d, cannot open file %s, since %s", pReader->pWal->cfg.vgId, fnameStr, terrstr());
     return -1;
   }
 
-  pRead->pIdxFile = pIdxTFile;
+  pReader->pIdxFile = pIdxFile;
   return 0;
 }
 
-int32_t walReadSeekVerImpl(SWalReader *pRead, int64_t ver) {
-  SWal *pWal = pRead->pWal;
+int32_t walReadSeekVerImpl(SWalReader *pReader, int64_t ver) {
+  SWal *pWal = pReader->pWal;
 
+  // bsearch in fileSet
   SWalFileInfo tmpInfo;
   tmpInfo.firstVer = ver;
-  // bsearch in fileSet
   SWalFileInfo *pRet = taosArraySearch(pWal->fileInfoSet, &tmpInfo, compareWalFileInfo, TD_LE);
   ASSERT(pRet != NULL);
-  if (pRead->curFileFirstVer != pRet->firstVer) {
+  if (pReader->curFileFirstVer != pRet->firstVer) {
     // error code was set inner
-    if (walReadChangeFile(pRead, pRet->firstVer) < 0) {
+    if (walReadChangeFile(pReader, pRet->firstVer) < 0) {
       return -1;
     }
   }
 
   // error code was set inner
-  if (walReadSeekFilePos(pRead, pRet->firstVer, ver) < 0) {
+  if (walReadSeekFilePos(pReader, pRet->firstVer, ver) < 0) {
     return -1;
   }
 
-  wDebug("wal version reset from %ld(invalid: %d) to %ld", pRead->curVersion, pRead->curInvalid, ver);
+  wDebug("wal version reset from %ld(invalid: %d) to %ld", pReader->curVersion, pReader->curInvalid, ver);
 
-  pRead->curVersion = ver;
+  pReader->curVersion = ver;
   return 0;
 }
 
-int32_t walReadSeekVer(SWalReader *pRead, int64_t ver) {
-  SWal *pWal = pRead->pWal;
-  if (!pRead->curInvalid && ver == pRead->curVersion) {
+int32_t walReadSeekVer(SWalReader *pReader, int64_t ver) {
+  SWal *pWal = pReader->pWal;
+  if (!pReader->curInvalid && ver == pReader->curVersion) {
     wDebug("wal version %ld match, no need to reset", ver);
     return 0;
   }
 
-  pRead->curInvalid = 1;
-  pRead->curVersion = ver;
+  pReader->curInvalid = 1;
+  pReader->curVersion = ver;
 
   if (ver > pWal->vers.lastVer || ver < pWal->vers.firstVer) {
-    wDebug("vgId:%d, invalid index:%" PRId64 ", first index:%" PRId64 ", last index:%" PRId64, pRead->pWal->cfg.vgId,
+    wDebug("vgId:%d, invalid index:%" PRId64 ", first index:%" PRId64 ", last index:%" PRId64, pReader->pWal->cfg.vgId,
            ver, pWal->vers.firstVer, pWal->vers.lastVer);
     terrno = TSDB_CODE_WAL_LOG_NOT_EXIST;
     return -1;
@@ -210,7 +215,7 @@ int32_t walReadSeekVer(SWalReader *pRead, int64_t ver) {
   if (ver < pWal->vers.snapshotVer) {
   }
 
-  if (walReadSeekVerImpl(pRead, ver) < 0) {
+  if (walReadSeekVerImpl(pReader, ver) < 0) {
     return -1;
   }
 
diff --git a/source/libs/wal/src/walRef.c b/source/libs/wal/src/walRef.c
new file mode 100644
index 0000000000000000000000000000000000000000..bd0f6fb1a8106d47b7c874f7e7ac3a99f9384911
--- /dev/null
+++ b/source/libs/wal/src/walRef.c
@@ -0,0 +1,89 @@
+/*
+ * Copyright (c) 2019 TAOS Data, Inc. <jhtao@taosdata.com>
+ *
+ * This program is free software: you can use, redistribute, and/or modify
+ * it under the terms of the GNU Affero General Public License, version 3
+ * or later ("AGPL"), as published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.
+ *
+ * You should have received a copy of the GNU Affero General Public License
+ * along with this program. If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#include "cJSON.h"
+#include "os.h"
+#include "taoserror.h"
+#include "tutil.h"
+#include "walInt.h"
+
+SWalRef *walOpenRef(SWal *pWal) {
+  SWalRef *pRef = taosMemoryCalloc(1, sizeof(SWalRef));
+  if (pRef == NULL) {
+    return NULL;
+  }
+  pRef->refId = tGenIdPI64();
+  pRef->refVer = -1;
+  pRef->refFile = -1;
+  pRef->pWal = pWal;
+  taosHashPut(pWal->pRefHash, &pRef->refId, sizeof(int64_t), &pRef, sizeof(void *));
+  return pRef;
+}
+
+void walCloseRef(SWal *pWal, int64_t refId) {
+  SWalRef *pRef = *(SWalRef **)taosHashGet(pWal->pRefHash, &refId, sizeof(int64_t));
+  taosHashRemove(pWal->pRefHash, &refId, sizeof(int64_t));
+  taosMemoryFree(pRef);
+}
+
+int32_t walRefVer(SWalRef *pRef, int64_t ver) {
+  SWal *pWal = pRef->pWal;
+  if (pRef->refVer != ver) {
+    taosThreadMutexLock(&pWal->mutex);
+    if (ver < pWal->vers.firstVer || ver > pWal->vers.lastVer) {
+      taosThreadMutexUnlock(&pWal->mutex);
+      terrno = TSDB_CODE_WAL_INVALID_VER;
+      return -1;
+    }
+
+    pRef->refVer = ver;
+    // bsearch in fileSet
+    SWalFileInfo tmpInfo;
+    tmpInfo.firstVer = ver;
+    SWalFileInfo *pRet = taosArraySearch(pWal->fileInfoSet, &tmpInfo, compareWalFileInfo, TD_LE);
+    ASSERT(pRet != NULL);
+    pRef->refFile = pRet->firstVer;
+
+    taosThreadMutexUnlock(&pWal->mutex);
+  }
+
+  return 0;
+}
+
+void walUnrefVer(SWalRef *pRef) {
+  pRef->refId = -1;
+  pRef->refFile = -1;
+}
+
+SWalRef *walRefCommittedVer(SWal *pWal) {
+  SWalRef *pRef = walOpenRef(pWal);
+  if (pRef == NULL) {
+    return NULL;
+  }
+  taosThreadMutexLock(&pWal->mutex);
+
+  int64_t ver = walGetCommittedVer(pWal);
+
+  pRef->refVer = ver;
+  // bsearch in fileSet
+  SWalFileInfo tmpInfo;
+  tmpInfo.firstVer = ver;
+  SWalFileInfo *pRet = taosArraySearch(pWal->fileInfoSet, &tmpInfo, compareWalFileInfo, TD_LE);
+  ASSERT(pRet != NULL);
+  pRef->refFile = pRet->firstVer;
+
+  taosThreadMutexUnlock(&pWal->mutex);
+  return pRef;
+}
diff --git a/source/libs/wal/src/walWrite.c b/source/libs/wal/src/walWrite.c
index d6348cc5dd78776b8a4d17dbb6492e0a63f6ba37..81500d80882f930e253771b835ac0f9e63f0f57b 100644
--- a/source/libs/wal/src/walWrite.c
+++ b/source/libs/wal/src/walWrite.c
@@ -26,7 +26,7 @@ int32_t walRestoreFromSnapshot(SWal *pWal, int64_t ver) {
     pIter = taosHashIterate(pWal->pRefHash, pIter);
     if (pIter == NULL) break;
     SWalRef *pRef = (SWalRef *)pIter;
-    if (pRef->ver != -1) {
+    if (pRef->refVer != -1) {
       taosHashCancelIterate(pWal->pRefHash, pIter);
       return -1;
     }
@@ -215,22 +215,23 @@ int32_t walRollback(SWal *pWal, int64_t ver) {
 
 static FORCE_INLINE int32_t walCheckAndRoll(SWal *pWal) {
   if (taosArrayGetSize(pWal->fileInfoSet) == 0) {
-    /*pWal->vers.firstVer = index;*/
     if (walRollImpl(pWal) < 0) {
       return -1;
     }
-  } else {
-    int64_t passed = walGetSeq() - pWal->lastRollSeq;
-    if (pWal->cfg.rollPeriod != -1 && pWal->cfg.rollPeriod != 0 && passed > pWal->cfg.rollPeriod) {
-      if (walRollImpl(pWal) < 0) {
-        return -1;
-      }
-    } else if (pWal->cfg.segSize != -1 && pWal->cfg.segSize != 0 && walGetLastFileSize(pWal) > pWal->cfg.segSize) {
-      if (walRollImpl(pWal) < 0) {
-        return -1;
-      }
+    return 0;
+  }
+
+  int64_t passed = walGetSeq() - pWal->lastRollSeq;
+  if (pWal->cfg.rollPeriod != -1 && pWal->cfg.rollPeriod != 0 && passed > pWal->cfg.rollPeriod) {
+    if (walRollImpl(pWal) < 0) {
+      return -1;
+    }
+  } else if (pWal->cfg.segSize != -1 && pWal->cfg.segSize != 0 && walGetLastFileSize(pWal) > pWal->cfg.segSize) {
+    if (walRollImpl(pWal) < 0) {
+      return -1;
     }
   }
+
   return 0;
 }
 
@@ -260,6 +261,16 @@ int32_t walEndSnapshot(SWal *pWal) {
   pWal->vers.snapshotVer = ver;
   int ts = taosGetTimestampSec();
 
+  int64_t minVerToDelete = ver;
+  void   *pIter = NULL;
+  while (1) {
+    pIter = taosHashIterate(pWal->pRefHash, pIter);
+    if (pIter == NULL) break;
+    SWalRef *pRef = *(SWalRef **)pIter;
+    if (pRef->refVer == -1) continue;
+    minVerToDelete = TMIN(minVerToDelete, pRef->refVer);
+  }
+
   int          deleteCnt = 0;
   int64_t      newTotSize = pWal->totSize;
   SWalFileInfo tmp;