diff --git a/src/client/src/tscAsync.c b/src/client/src/tscAsync.c
index 8c194c031d81d899af22b0be90be87072d8a8b51..6ab4eeaa8a3dd54eb61f14d75d97e34e64a2390d 100644
--- a/src/client/src/tscAsync.c
+++ b/src/client/src/tscAsync.c
@@ -54,7 +54,7 @@ void doAsyncQuery(STscObj* pObj, SSqlObj* pSql, void (*fp)(), void* param, const
     return;
   }
 
-  strtolower(pSql->sqlstr, sqlstr);
+  strntolower(pSql->sqlstr, sqlstr, sqlLen);
 
   tscDebugL("%p SQL: %s", pSql, pSql->sqlstr);
   pSql->cmd.curSql = pSql->sqlstr;
@@ -564,8 +564,8 @@ void tscTableMetaCallBack(void *param, TAOS_RES *res, int code) {
     tscDebug("%p stream:%p meta is updated, start new query, command:%d", pSql, pSql->pStream, pSql->cmd.command);
     if (!pSql->cmd.parseFinished) {
       tsParseSql(pSql, false);
-      sem_post(&pSql->rspSem);
     }
+    (*pSql->fp)(pSql->param, pSql, code);
 
     return;
   }
diff --git a/src/client/src/tscSQLParser.c b/src/client/src/tscSQLParser.c
index 9d80c7ed50944f14a5687d3034d5368552861cb1..f76a1341d24beec8295011f01fe4bd5e57e3b0e8 100644
--- a/src/client/src/tscSQLParser.c
+++ b/src/client/src/tscSQLParser.c
@@ -4642,21 +4642,24 @@ typedef struct SDNodeDynConfOption {
 } SDNodeDynConfOption;
 
 
-int32_t validateEp(char* ep) {
+int32_t validateEp(char* ep) {  
   char buf[TSDB_EP_LEN + 1] = {0};
   tstrncpy(buf, ep, TSDB_EP_LEN);
 
-  char *pos = strchr(buf, ':');
-  if (NULL == pos) {   
-    return TSDB_CODE_TSC_INVALID_SQL;
+  char* pos = strchr(buf, ':');
+  if (NULL == pos) {
+    int32_t val = strtol(ep, NULL, 10);
+    if (val <= 0 || val > 65536) {
+      return TSDB_CODE_TSC_INVALID_SQL;
+    }
+  } else {
+    uint16_t port = atoi(pos + 1);
+    if (0 == port) {
+      return TSDB_CODE_TSC_INVALID_SQL;
+    }
   }
-  
-  uint16_t port = atoi(pos+1);
-  if (0 == port) {   
-    return TSDB_CODE_TSC_INVALID_SQL;
-  }  
 
-  return TSDB_CODE_SUCCESS;   
+  return TSDB_CODE_SUCCESS;
 }
 
 int32_t validateDNodeConfig(tDCLSQL* pOptions) {
@@ -4664,13 +4667,13 @@ int32_t validateDNodeConfig(tDCLSQL* pOptions) {
     return TSDB_CODE_TSC_INVALID_SQL;
   }
 
-  const int DNODE_DYNAMIC_CFG_OPTIONS_SIZE = 17;
+  const int DNODE_DYNAMIC_CFG_OPTIONS_SIZE = 19;
   const SDNodeDynConfOption DNODE_DYNAMIC_CFG_OPTIONS[] = {
       {"resetLog", 8},       {"resetQueryCache", 15},  {"debugFlag", 9},     {"mDebugFlag", 10},
       {"dDebugFlag", 10},    {"sdbDebugFlag", 12},     {"vDebugFlag", 10},   {"cDebugFlag", 10},
       {"httpDebugFlag", 13}, {"monitorDebugFlag", 16}, {"rpcDebugFlag", 12}, {"uDebugFlag", 10},
       {"tmrDebugFlag", 12},  {"qDebugflag", 10},       {"sDebugflag", 10},   {"tsdbDebugFlag", 13},
-      {"monitor", 7}};
+      {"mqttDebugFlag", 13}, {"wDebugFlag", 10},       {"monitor", 7}};
 
   SSQLToken* pOptionToken = &pOptions->a[1];
 
@@ -4694,7 +4697,7 @@ int32_t validateDNodeConfig(tDCLSQL* pOptions) {
     SSQLToken* pValToken = &pOptions->a[2];
 
     int32_t val = strtol(pValToken->z, NULL, 10);
-    if (val < 131 || val > 199) {
+    if (val < 0 || val > 256) {
       /* options value is out of valid range */
       return TSDB_CODE_TSC_INVALID_SQL;
     }
diff --git a/src/client/src/tscSql.c b/src/client/src/tscSql.c
index 5d5e5469430721079753ff3d4badd0e40e77d1d2..0677463d8d01df899a377c7390a22743aa9b22ed 100644
--- a/src/client/src/tscSql.c
+++ b/src/client/src/tscSql.c
@@ -263,12 +263,29 @@ TAOS_RES* taos_query(TAOS *taos, const char *sqlstr) {
   return pSql;
 }
 TAOS_RES* taos_query_c(TAOS *taos, const char *sqlstr, uint32_t sqlLen) {
-  char* buf = malloc(sqlLen + 1);
-  buf[sqlLen] = 0;
-  strncpy(buf, sqlstr, sqlLen);
-  TAOS_RES *res = taos_query(taos, buf);
-  free(buf);
-  return res; 
+  STscObj *pObj = (STscObj *)taos;
+  if (pObj == NULL || pObj->signature != pObj) {
+    terrno = TSDB_CODE_TSC_DISCONNECTED;
+    return NULL;
+  }
+  
+  if (sqlLen > tsMaxSQLStringLen) {
+    tscError("sql string exceeds max length:%d", tsMaxSQLStringLen);
+    terrno = TSDB_CODE_TSC_INVALID_SQL;
+    return NULL;
+  }
+  
+  SSqlObj* pSql = calloc(1, sizeof(SSqlObj));
+  if (pSql == NULL) {
+    tscError("failed to malloc sqlObj");
+    terrno = TSDB_CODE_TSC_OUT_OF_MEMORY;
+    return NULL;
+  }
+  
+  doAsyncQuery(pObj, pSql, waitForQueryRsp, taos, sqlstr, sqlLen);
+
+  tsem_wait(&pSql->rspSem);
+  return pSql; 
 }
 int taos_result_precision(TAOS_RES *res) {
   SSqlObj *pSql = (SSqlObj *)res;
diff --git a/src/client/src/tscStream.c b/src/client/src/tscStream.c
index 6cc27a4cfe0991072bee92b7e831fb0736923b38..7c188ec96975f28e1bc5d692ed4e2c98ac505afb 100644
--- a/src/client/src/tscStream.c
+++ b/src/client/src/tscStream.c
@@ -70,6 +70,7 @@ static void tscProcessStreamLaunchQuery(SSchedMsg *pMsg) {
   SSqlObj *   pSql = pStream->pSql;
 
   pSql->fp = tscProcessStreamQueryCallback;
+  pSql->fetchFp = tscProcessStreamQueryCallback;
   pSql->param = pStream;
   pSql->res.completed = false;
   
@@ -471,6 +472,41 @@ static void setErrorInfo(SSqlObj* pSql, int32_t code, char* info) {
   }
 }
 
+static void tscCreateStream(void *param, TAOS_RES *res, int code) {
+  SSqlStream* pStream = (SSqlStream*)param;
+  SSqlObj* pSql = pStream->pSql;
+  SSqlCmd* pCmd = &pSql->cmd;
+
+  if (code != TSDB_CODE_SUCCESS) {
+    setErrorInfo(pSql, code, pCmd->payload);
+    tscError("%p open stream failed, sql:%s, reason:%s, code:0x%08x", pSql, pSql->sqlstr, pCmd->payload, code);
+    pStream->fp(pStream->param, NULL, NULL);
+    return;
+  }
+
+  SQueryInfo* pQueryInfo = tscGetQueryInfoDetail(pCmd, 0);
+  STableMetaInfo* pTableMetaInfo = tscGetMetaInfo(pQueryInfo, 0);
+  STableComInfo tinfo = tscGetTableInfo(pTableMetaInfo->pTableMeta);
+  
+  pStream->isProject = isProjectStream(pQueryInfo);
+  pStream->precision = tinfo.precision;
+
+  pStream->ctime = taosGetTimestamp(pStream->precision);
+  pStream->etime = pQueryInfo->window.ekey;
+
+  tscAddIntoStreamList(pStream);
+
+  tscSetSlidingWindowInfo(pSql, pStream);
+  pStream->stime = tscGetStreamStartTimestamp(pSql, pStream, pStream->stime);
+
+  int64_t starttime = tscGetLaunchTimestamp(pStream);
+  pCmd->command = TSDB_SQL_SELECT;
+  taosTmrReset(tscProcessStreamTimer, starttime, pStream, tscTmr, &pStream->pTimer);
+
+  tscDebug("%p stream:%p is opened, query on:%s, interval:%" PRId64 ", sliding:%" PRId64 ", first launched in:%" PRId64 ", sql:%s", pSql,
+           pStream, pTableMetaInfo->name, pStream->interval, pStream->slidingTime, starttime, pSql->sqlstr);
+}
+
 TAOS_STREAM *taos_open_stream(TAOS *taos, const char *sqlstr, void (*fp)(void *param, TAOS_RES *, TAOS_ROW row),
                               int64_t stime, void *param, void (*callback)(void *)) {
   STscObj *pObj = (STscObj *)taos;
@@ -482,7 +518,6 @@ TAOS_STREAM *taos_open_stream(TAOS *taos, const char *sqlstr, void (*fp)(void *p
   }
 
   pSql->signature = pSql;
-  pSql->param = pSql;
   pSql->pTscObj = pObj;
 
   SSqlCmd *pCmd = &pSql->cmd;
@@ -494,7 +529,14 @@ TAOS_STREAM *taos_open_stream(TAOS *taos, const char *sqlstr, void (*fp)(void *p
     tscFreeSqlObj(pSql);
     return NULL;
   }
+
+  pStream->stime = stime;
+  pStream->fp = fp;
+  pStream->callback = callback;
+  pStream->param = param;
+  pStream->pSql = pSql;
   pSql->pStream = pStream;
+  pSql->param = pStream;
 
   pSql->sqlstr = calloc(1, strlen(sqlstr) + 1);
   if (pSql->sqlstr == NULL) {
@@ -507,45 +549,18 @@ TAOS_STREAM *taos_open_stream(TAOS *taos, const char *sqlstr, void (*fp)(void *p
   tscDebugL("%p SQL: %s", pSql, pSql->sqlstr);
   tsem_init(&pSql->rspSem, 0, 0);
 
+  pSql->fp = tscCreateStream;
+  pSql->fetchFp = tscCreateStream;
   int32_t code = tsParseSql(pSql, true);
-  if (code == TSDB_CODE_TSC_ACTION_IN_PROGRESS) {
-    sem_wait(&pSql->rspSem);
-  }
-
-  if (pRes->code != TSDB_CODE_SUCCESS) {
-    setErrorInfo(pSql, pRes->code, pCmd->payload);
-
-    tscError("%p open stream failed, sql:%s, reason:%s, code:0x%08x", pSql, sqlstr, pCmd->payload, pRes->code);
+  if (code == TSDB_CODE_SUCCESS) {
+    tscCreateStream(pStream, pSql, code);
+  } else if (code != TSDB_CODE_TSC_ACTION_IN_PROGRESS) {
+    tscError("%p open stream failed, sql:%s, code:%s", pSql, sqlstr, tstrerror(pRes->code));
     tscFreeSqlObj(pSql);
+    free(pStream);
     return NULL;
   }
 
-  SQueryInfo* pQueryInfo = tscGetQueryInfoDetail(pCmd, 0);
-  STableMetaInfo* pTableMetaInfo = tscGetMetaInfo(pQueryInfo, 0);
-  STableComInfo tinfo = tscGetTableInfo(pTableMetaInfo->pTableMeta);
-  
-  pStream->isProject = isProjectStream(pQueryInfo);
-  pStream->fp = fp;
-  pStream->callback = callback;
-  pStream->param = param;
-  pStream->pSql = pSql;
-  pStream->precision = tinfo.precision;
-
-  pStream->ctime = taosGetTimestamp(pStream->precision);
-  pStream->etime = pQueryInfo->window.ekey;
-
-  tscAddIntoStreamList(pStream);
-
-  tscSetSlidingWindowInfo(pSql, pStream);
-  pStream->stime = tscGetStreamStartTimestamp(pSql, pStream, stime);
-
-  int64_t starttime = tscGetLaunchTimestamp(pStream);
-  pCmd->command = TSDB_SQL_SELECT;
-  taosTmrReset(tscProcessStreamTimer, starttime, pStream, tscTmr, &pStream->pTimer);
-
-  tscDebug("%p stream:%p is opened, query on:%s, interval:%" PRId64 ", sliding:%" PRId64 ", first launched in:%" PRId64 ", sql:%s", pSql,
-           pStream, pTableMetaInfo->name, pStream->interval, pStream->slidingTime, starttime, sqlstr);
-
   return pStream;
 }
 
diff --git a/src/common/src/tdataformat.c b/src/common/src/tdataformat.c
index 12ea4ad78d18a5f2b09daabb71093c153d30aca7..719d80aa775bf3b5abe3065ef7eca799d452e315 100644
--- a/src/common/src/tdataformat.c
+++ b/src/common/src/tdataformat.c
@@ -318,7 +318,7 @@ SDataCols *tdNewDataCols(int maxRowSize, int maxCols, int maxRows) {
   pCols->maxPoints = maxRows;
   pCols->bufSize = maxRowSize * maxRows;
 
-  pCols->buf = malloc(pCols->bufSize);
+  pCols->buf = calloc(1, pCols->bufSize);
   if (pCols->buf == NULL) {
     free(pCols);
     return NULL;
diff --git a/src/cq/src/cqMain.c b/src/cq/src/cqMain.c
index 04d3a6fd6dd40382f7e9bc03820e64df59a04950..51cd471a6b66526228b85be1c8dbc6f033d2515f 100644
--- a/src/cq/src/cqMain.c
+++ b/src/cq/src/cqMain.c
@@ -23,6 +23,7 @@
 #include "taos.h"
 #include "taosdef.h"
 #include "taosmsg.h"
+#include "ttimer.h"
 #include "tcq.h"
 #include "tdataformat.h"
 #include "tglobal.h"
@@ -45,10 +46,12 @@ typedef struct {
   struct SCqObj *pHead;
   void    *dbConn;
   int      master;
+  void    *tmrCtrl;
   pthread_mutex_t mutex;
 } SCqContext;
 
 typedef struct SCqObj {
+  tmr_h          tmrId;
   uint64_t       uid;
   int32_t        tid;      // table ID
   int            rowSize;  // bytes of a row
@@ -66,13 +69,14 @@ static void cqProcessStreamRes(void *param, TAOS_RES *tres, TAOS_ROW row);
 static void cqCreateStream(SCqContext *pContext, SCqObj *pObj);
 
 void *cqOpen(void *ahandle, const SCqCfg *pCfg) {
-  
   SCqContext *pContext = calloc(sizeof(SCqContext), 1);
   if (pContext == NULL) {
     terrno = TAOS_SYSTEM_ERROR(errno);
     return NULL;
   }
 
+  pContext->tmrCtrl = taosTmrInit(0, 0, 0, "CQ");
+
   tstrncpy(pContext->user, pCfg->user, sizeof(pContext->user));
   tstrncpy(pContext->pass, pCfg->pass, sizeof(pContext->pass));
   const char* db = pCfg->db;
@@ -99,6 +103,9 @@ void cqClose(void *handle) {
   SCqContext *pContext = handle;
   if (handle == NULL) return;
 
+  taosTmrCleanUp(pContext->tmrCtrl);
+  pContext->tmrCtrl = NULL;
+
   // stop all CQs
   cqStop(pContext);
 
@@ -154,8 +161,10 @@ void cqStop(void *handle) {
       taos_close_stream(pObj->pStream);
       pObj->pStream = NULL;
       cTrace("vgId:%d, id:%d CQ:%s is closed", pContext->vgId, pObj->tid, pObj->sqlStr);
+    } else {
+      taosTmrStop(pObj->tmrId);
+      pObj->tmrId = 0;
     }
-
     pObj = pObj->next;
   }
 
@@ -211,8 +220,13 @@ void cqDrop(void *handle) {
   }
 
   // free the resources associated
-  if (pObj->pStream) taos_close_stream(pObj->pStream);
-  pObj->pStream = NULL;
+  if (pObj->pStream) {
+    taos_close_stream(pObj->pStream);
+    pObj->pStream = NULL;
+  } else {
+    taosTmrStop(pObj->tmrId);
+    pObj->tmrId = 0;
+  }
 
   cTrace("vgId:%d, id:%d CQ:%s is dropped", pContext->vgId, pObj->tid, pObj->sqlStr); 
   tdFreeSchema(pObj->pSchema);
@@ -222,18 +236,30 @@ void cqDrop(void *handle) {
   pthread_mutex_unlock(&pContext->mutex);
 }
 
-static void cqCreateStream(SCqContext *pContext, SCqObj *pObj) {
+static void cqProcessCreateTimer(void *param, void *tmrId) {
+  SCqObj* pObj = (SCqObj*)param;
+  SCqContext* pContext = pObj->pContext;
+
   if (pContext->dbConn == NULL) {
     pContext->dbConn = taos_connect("localhost", pContext->user, pContext->pass, pContext->db, 0);
     if (pContext->dbConn == NULL) {
       cError("vgId:%d, failed to connect to TDengine(%s)", pContext->vgId, tstrerror(terrno));
-      return;
     }
   }
+  
+  cqCreateStream(pContext, pObj);
+}
 
-  int64_t lastKey = 0;
+static void cqCreateStream(SCqContext *pContext, SCqObj *pObj) {
   pObj->pContext = pContext;
-  pObj->pStream = taos_open_stream(pContext->dbConn, pObj->sqlStr, cqProcessStreamRes, lastKey, pObj, NULL);
+
+  if (pContext->dbConn == NULL) {
+    pObj->tmrId = taosTmrStart(cqProcessCreateTimer, 1000, pObj, pContext->tmrCtrl);
+    return;
+  }
+  pObj->tmrId = 0;
+
+  pObj->pStream = taos_open_stream(pContext->dbConn, pObj->sqlStr, cqProcessStreamRes, 0, pObj, NULL);
   if (pObj->pStream) {
     pContext->num++;
     cTrace("vgId:%d, id:%d CQ:%s is openned", pContext->vgId, pObj->tid, pObj->sqlStr);
diff --git a/src/dnode/inc/dnodeModule.h b/src/dnode/inc/dnodeModule.h
index 6a6da0a2a52844e4a2c42bad64658c93b48fffae..8618de324446ca3f2504d15a6422bcca3a4b51b0 100644
--- a/src/dnode/inc/dnodeModule.h
+++ b/src/dnode/inc/dnodeModule.h
@@ -22,7 +22,6 @@ extern "C" {
 
 int32_t dnodeInitModules();
 void    dnodeStartModules();
-void    dnodeStartStream();
 void    dnodeCleanupModules();
 void    dnodeProcessModuleStatus(uint32_t moduleStatus);
 
diff --git a/src/dnode/src/dnodeMain.c b/src/dnode/src/dnodeMain.c
index 987a1899597f495730a391e6bdbde7fb862731c3..6476bb78314f76ae02cbaae0dd04547bc7565313 100644
--- a/src/dnode/src/dnodeMain.c
+++ b/src/dnode/src/dnodeMain.c
@@ -123,7 +123,6 @@ int32_t dnodeInitSystem() {
 
   dnodeStartModules();
   dnodeSetRunStatus(TSDB_DNODE_RUN_STATUS_RUNING);
-  dnodeStartStream();
 
   dInfo("TDengine is initialized successfully");
 
diff --git a/src/dnode/src/dnodeMgmt.c b/src/dnode/src/dnodeMgmt.c
index 338fcd287cefe8813e29ff8da7f40a60cf59fad5..8e1696c80207de54b57c9c497e589d2b7b6137ac 100644
--- a/src/dnode/src/dnodeMgmt.c
+++ b/src/dnode/src/dnodeMgmt.c
@@ -354,23 +354,6 @@ static int32_t dnodeOpenVnodes() {
   return TSDB_CODE_SUCCESS;
 }
 
-void dnodeStartStream() {
-  int32_t vnodeList[TSDB_MAX_VNODES] = {0};
-  int32_t numOfVnodes = 0;
-  int32_t status = vnodeGetVnodeList(vnodeList, &numOfVnodes);
-
-  if (status != TSDB_CODE_SUCCESS) {
-    dInfo("get dnode list failed");
-    return;
-  }
-
-  for (int32_t i = 0; i < numOfVnodes; ++i) {
-    vnodeStartStream(vnodeList[i]);
-  }
-
-  dInfo("streams started");
-}
-
 static void dnodeCloseVnodes() {
   int32_t vnodeList[TSDB_MAX_VNODES]= {0};
   int32_t numOfVnodes = 0;
@@ -416,7 +399,7 @@ static void* dnodeParseVnodeMsg(SRpcMsg *rpcMsg) {
 static int32_t dnodeProcessCreateVnodeMsg(SRpcMsg *rpcMsg) {
   SMDCreateVnodeMsg *pCreate = dnodeParseVnodeMsg(rpcMsg);
 
-  void *pVnode = vnodeAcquireVnode(pCreate->cfg.vgId);
+  void *pVnode = vnodeAcquire(pCreate->cfg.vgId);
   if (pVnode != NULL) {
     dDebug("vgId:%d, already exist, return success", pCreate->cfg.vgId);
     vnodeRelease(pVnode);
@@ -430,7 +413,7 @@ static int32_t dnodeProcessCreateVnodeMsg(SRpcMsg *rpcMsg) {
 static int32_t dnodeProcessAlterVnodeMsg(SRpcMsg *rpcMsg) {
   SMDAlterVnodeMsg *pAlter = dnodeParseVnodeMsg(rpcMsg);
 
-  void *pVnode = vnodeAcquireVnode(pAlter->cfg.vgId);
+  void *pVnode = vnodeAcquire(pAlter->cfg.vgId);
   if (pVnode != NULL) {
     dDebug("vgId:%d, alter vnode msg is received", pAlter->cfg.vgId);
     int32_t code = vnodeAlter(pVnode, pAlter);
@@ -723,6 +706,7 @@ static void dnodeSendStatusMsg(void *handle, void *tmrId) {
 
   // fill cluster cfg parameters
   pStatus->clusterCfg.numOfMnodes        = htonl(tsNumOfMnodes);
+  pStatus->clusterCfg.enableBalance      = htonl(tsEnableBalance);
   pStatus->clusterCfg.mnodeEqualVnodeNum = htonl(tsMnodeEqualVnodeNum);
   pStatus->clusterCfg.offlineThreshold   = htonl(tsOfflineThreshold);
   pStatus->clusterCfg.statusInterval     = htonl(tsStatusInterval);
diff --git a/src/dnode/src/dnodeVRead.c b/src/dnode/src/dnodeVRead.c
index 66135a93e9e6c824ce5219a4f5ef65b230bbce95..bbea1a5e0bb52a56cfbf5a23dd29a17e094586a9 100644
--- a/src/dnode/src/dnodeVRead.c
+++ b/src/dnode/src/dnodeVRead.c
@@ -91,23 +91,21 @@ void dnodeDispatchToVnodeReadQueue(SRpcMsg *pMsg) {
   int32_t     queuedMsgNum = 0;
   int32_t     leftLen      = pMsg->contLen;
   char        *pCont       = (char *) pMsg->pCont;
-  void        *pVnode;
 
   while (leftLen > 0) {
     SMsgHead *pHead = (SMsgHead *) pCont;
     pHead->vgId    = htonl(pHead->vgId);
     pHead->contLen = htonl(pHead->contLen);
 
-    pVnode = vnodeAcquireVnode(pHead->vgId);
+    taos_queue queue = vnodeAcquireRqueue(pHead->vgId);
 
-    if (pVnode == NULL) {
+    if (queue == NULL) {
       leftLen -= pHead->contLen;
       pCont -= pHead->contLen;
       continue;
     }
 
     // put message into queue
-    taos_queue queue = vnodeGetRqueue(pVnode);
     SReadMsg *pRead = (SReadMsg *)taosAllocateQitem(sizeof(SReadMsg));
     pRead->rpcMsg      = *pMsg;
     pRead->pCont       = pCont;
@@ -175,18 +173,6 @@ void dnodeFreeVnodeRqueue(void *rqueue) {
   // dynamically adjust the number of threads
 }
 
-void dnodePutItemIntoReadQueue(void *pVnode, void *qhandle) {
-  SReadMsg *pRead = (SReadMsg *)taosAllocateQitem(sizeof(SReadMsg));
-  pRead->rpcMsg.msgType = TSDB_MSG_TYPE_QUERY;
-  pRead->pCont = qhandle;
-  pRead->contLen = 0;
-
-  assert(pVnode != NULL);
-  taos_queue queue = vnodeAcquireRqueue(pVnode);
-
-  taosWriteQitem(queue, TAOS_QTYPE_QUERY, pRead);
-}
-
 void dnodeSendRpcReadRsp(void *pVnode, SReadMsg *pRead, int32_t code) {
   SRpcMsg rpcRsp = {
     .handle  = pRead->rpcMsg.handle,
diff --git a/src/dnode/src/dnodeVWrite.c b/src/dnode/src/dnodeVWrite.c
index ba36e537a6c2b7a6327ef17ed0be83b880009310..dc09a03e1497cb52718279b542e3318fb2789d08 100644
--- a/src/dnode/src/dnodeVWrite.c
+++ b/src/dnode/src/dnodeVWrite.c
@@ -104,7 +104,7 @@ void dnodeDispatchToVnodeWriteQueue(SRpcMsg *pMsg) {
   pHead->vgId     = htonl(pHead->vgId);
   pHead->contLen  = htonl(pHead->contLen);
 
-  taos_queue queue = vnodeGetWqueue(pHead->vgId);
+  taos_queue queue = vnodeAcquireWqueue(pHead->vgId);
   if (queue) {
     // put message into queue
     SWriteMsg *pWrite = (SWriteMsg *)taosAllocateQitem(sizeof(SWriteMsg));
diff --git a/src/inc/dnode.h b/src/inc/dnode.h
index 096aae58f2ad9cb157ba5b700581bdf52a23f6eb..b561c407a3415d7db27333d96e21a72d4f159d8b 100644
--- a/src/inc/dnode.h
+++ b/src/inc/dnode.h
@@ -53,7 +53,6 @@ void *dnodeAllocateVnodeWqueue(void *pVnode);
 void  dnodeFreeVnodeWqueue(void *queue);
 void *dnodeAllocateVnodeRqueue(void *pVnode);
 void  dnodeFreeVnodeRqueue(void *rqueue);
-void  dnodePutItemIntoReadQueue(void *pVnode, void *qhandle);
 void  dnodeSendRpcVnodeWriteRsp(void *pVnode, void *param, int32_t code);
 
 int32_t dnodeAllocateMnodePqueue();
diff --git a/src/inc/taosmsg.h b/src/inc/taosmsg.h
index e30efcfd372866c3133e99847143c6a590e72bb7..b7afaf1e065074018d9725796434776dae1a9158 100644
--- a/src/inc/taosmsg.h
+++ b/src/inc/taosmsg.h
@@ -54,12 +54,11 @@ TAOS_DEFINE_MESSAGE_TYPE( TSDB_MSG_TYPE_MD_CREATE_TABLE, "create-table" )
 TAOS_DEFINE_MESSAGE_TYPE( TSDB_MSG_TYPE_MD_DROP_TABLE, "drop-table" )	
 TAOS_DEFINE_MESSAGE_TYPE( TSDB_MSG_TYPE_MD_ALTER_TABLE, "alter-table" )	
 TAOS_DEFINE_MESSAGE_TYPE( TSDB_MSG_TYPE_MD_CREATE_VNODE, "create-vnode" )
-TAOS_DEFINE_MESSAGE_TYPE( TSDB_MSG_TYPE_MD_ALTER_VNODE, "alter-vnode" )
 TAOS_DEFINE_MESSAGE_TYPE( TSDB_MSG_TYPE_MD_DROP_VNODE, "drop-vnode" )	
 TAOS_DEFINE_MESSAGE_TYPE( TSDB_MSG_TYPE_MD_DROP_STABLE, "drop-stable" )
 TAOS_DEFINE_MESSAGE_TYPE( TSDB_MSG_TYPE_MD_ALTER_STREAM, "alter-stream" )
 TAOS_DEFINE_MESSAGE_TYPE( TSDB_MSG_TYPE_MD_CONFIG_DNODE, "config-dnode" )
-TAOS_DEFINE_MESSAGE_TYPE( TSDB_MSG_TYPE_DUMMY4, "dummy4" )
+TAOS_DEFINE_MESSAGE_TYPE( TSDB_MSG_TYPE_MD_ALTER_VNODE, "alter-vnode" )
 TAOS_DEFINE_MESSAGE_TYPE( TSDB_MSG_TYPE_DUMMY5, "dummy5" )
 TAOS_DEFINE_MESSAGE_TYPE( TSDB_MSG_TYPE_DUMMY6, "dummy6" )
 TAOS_DEFINE_MESSAGE_TYPE( TSDB_MSG_TYPE_DUMMY7, "dummy7" )
@@ -564,15 +563,16 @@ typedef struct {
 
 typedef struct {
   int32_t  numOfMnodes;               // tsNumOfMnodes
+  int32_t  enableBalance;             // tsEnableBalance
   int32_t  mnodeEqualVnodeNum;        // tsMnodeEqualVnodeNum
   int32_t  offlineThreshold;          // tsOfflineThreshold
   int32_t  statusInterval;            // tsStatusInterval
+  int32_t  maxtablesPerVnode;
+  int32_t  maxVgroupsPerDb;
   char     arbitrator[TSDB_EP_LEN];   // tsArbitrator
   char     timezone[64];              // tsTimezone
   char     locale[TSDB_LOCALE_LEN];   // tsLocale
   char     charset[TSDB_LOCALE_LEN];  // tsCharset
-  int32_t  maxtablesPerVnode;
-  int32_t  maxVgroupsPerDb;
 } SClusterCfg;
 
 typedef struct {
diff --git a/src/inc/tsdb.h b/src/inc/tsdb.h
index 3059fd2435e8db125305cc0db1f0d74fd5d4302c..e46ea39a59495991238cde777f7c31ea72aa87ac 100644
--- a/src/inc/tsdb.h
+++ b/src/inc/tsdb.h
@@ -116,7 +116,6 @@ int   tsdbCreateTable(TSDB_REPO_T *repo, STableCfg *pCfg);
 int   tsdbDropTable(TSDB_REPO_T *pRepo, STableId tableId);
 int   tsdbUpdateTableTagValue(TSDB_REPO_T *repo, SUpdateTableTagValMsg *pMsg);
 TSKEY tsdbGetTableLastKey(TSDB_REPO_T *repo, uint64_t uid);
-void  tsdbStartStream(TSDB_REPO_T *repo);
 
 uint32_t tsdbGetFileInfo(TSDB_REPO_T *repo, char *name, uint32_t *index, uint32_t eindex, int32_t *size);
 
diff --git a/src/inc/tsync.h b/src/inc/tsync.h
index 972db294f62a35ba7910576534f4291c021b6272..65b91d87e479abd4c0b497cf4b95bc561db8fae5 100644
--- a/src/inc/tsync.h
+++ b/src/inc/tsync.h
@@ -79,7 +79,7 @@ typedef void     (*FConfirmForward)(void *ahandle, void *mhandle, int32_t code);
 typedef void     (*FNotifyRole)(void *ahandle, int8_t role);
 
 // when data file is synced successfully, notity app
-typedef void     (*FNotifyFileSynced)(void *ahandle, uint64_t fversion);
+typedef int      (*FNotifyFileSynced)(void *ahandle, uint64_t fversion);
 
 typedef struct {
   int32_t    vgId;      // vgroup ID
diff --git a/src/inc/vnode.h b/src/inc/vnode.h
index 1e6cfa97006e110f5ce1e36073f165540adeda26..15ddb6afee7c3ac2914df8133df24f6ef80a0a8a 100644
--- a/src/inc/vnode.h
+++ b/src/inc/vnode.h
@@ -22,10 +22,10 @@ extern "C" {
 
 typedef enum _VN_STATUS {
   TAOS_VN_STATUS_INIT,
-  TAOS_VN_STATUS_UPDATING,
   TAOS_VN_STATUS_READY,
   TAOS_VN_STATUS_CLOSING,
-  TAOS_VN_STATUS_DELETING,
+  TAOS_VN_STATUS_UPDATING,
+  TAOS_VN_STATUS_RESET,
 } EVnStatus;
 
 typedef struct {
@@ -44,17 +44,13 @@ typedef struct {
 int32_t vnodeCreate(SMDCreateVnodeMsg *pVnodeCfg);
 int32_t vnodeDrop(int32_t vgId);
 int32_t vnodeOpen(int32_t vgId, char *rootDir);
-int32_t vnodeStartStream(int32_t vgId);
 int32_t vnodeAlter(void *pVnode, SMDCreateVnodeMsg *pVnodeCfg);
 int32_t vnodeClose(int32_t vgId);
 
-void    vnodeRelease(void *pVnode);
-void*   vnodeAcquireVnode(int32_t vgId); // add refcount
-void*   vnodeGetVnode(int32_t vgId);      // keep refcount unchanged
-
-void*   vnodeAcquireRqueue(void *);
-void*   vnodeGetRqueue(void *);
-void*   vnodeGetWqueue(int32_t vgId);
+void*   vnodeAcquire(int32_t vgId);        // add refcount
+void*   vnodeAcquireRqueue(int32_t vgId);  // add refCount, get read queue 
+void*   vnodeAcquireWqueue(int32_t vgId);  // add recCount, get write queue
+void    vnodeRelease(void *pVnode);        // dec refCount
 void*   vnodeGetWal(void *pVnode);
 
 int32_t vnodeProcessWrite(void *pVnode, int qtype, void *pHead, void *item);
diff --git a/src/mnode/src/mnodeDnode.c b/src/mnode/src/mnodeDnode.c
index a65f54cd8bd186adaf67bc5c45ebe3ea933a4c75..06d79bd7e11eca1f8381777667e5d4844be8b440 100644
--- a/src/mnode/src/mnodeDnode.c
+++ b/src/mnode/src/mnodeDnode.c
@@ -269,18 +269,37 @@ void mnodeUpdateDnode(SDnodeObj *pDnode) {
 }
 
 static int32_t mnodeProcessCfgDnodeMsg(SMnodeMsg *pMsg) {
+  if (strcmp(pMsg->pUser->user, TSDB_DEFAULT_USER) != 0) {
+    mError("failed to cfg dnode, no rights");
+    return TSDB_CODE_MND_NO_RIGHTS;
+  }
+  
   SCMCfgDnodeMsg *pCmCfgDnode = pMsg->rpcMsg.pCont;
   if (pCmCfgDnode->ep[0] == 0) {
-    strcpy(pCmCfgDnode->ep, tsLocalEp);
-  } else {
-    // TODO temporary disabled for compiling: strcpy(pCmCfgDnode->ep, pCmCfgDnode->ep); 
+    tstrncpy(pCmCfgDnode->ep, tsLocalEp, TSDB_EP_LEN);
+  } 
+
+  int32_t dnodeId = 0;
+  char* pos = strchr(pCmCfgDnode->ep, ':');
+  if (NULL == pos) {
+    dnodeId = strtol(pCmCfgDnode->ep, NULL, 10);
+    if (dnodeId <= 0 || dnodeId > 65536) {
+      mError("failed to cfg dnode, invalid dnodeId:%s", pCmCfgDnode->ep);
+      return TSDB_CODE_MND_DNODE_NOT_EXIST;
+    }
   }
 
-  if (strcmp(pMsg->pUser->user, TSDB_DEFAULT_USER) != 0) {
-    return TSDB_CODE_MND_NO_RIGHTS;
+  SRpcIpSet ipSet = mnodeGetIpSetFromIp(pCmCfgDnode->ep);
+  if (dnodeId != 0) {
+    SDnodeObj *pDnode = mnodeGetDnode(dnodeId);
+    if (pDnode == NULL) {
+      mError("failed to cfg dnode, invalid dnodeId:%d", dnodeId);
+      return TSDB_CODE_MND_DNODE_NOT_EXIST;
+    }
+    ipSet = mnodeGetIpSetFromIp(pDnode->dnodeEp);
+    mnodeDecDnodeRef(pDnode);
   }
 
-  SRpcIpSet ipSet = mnodeGetIpSetFromIp(pCmCfgDnode->ep);
   SMDCfgDnodeMsg *pMdCfgDnode = rpcMallocCont(sizeof(SMDCfgDnodeMsg));
   strcpy(pMdCfgDnode->ep, pCmCfgDnode->ep);
   strcpy(pMdCfgDnode->config, pCmCfgDnode->config);
@@ -292,9 +311,9 @@ static int32_t mnodeProcessCfgDnodeMsg(SMnodeMsg *pMsg) {
     .pCont = pMdCfgDnode,
     .contLen = sizeof(SMDCfgDnodeMsg)
   };
-  dnodeSendMsgToDnode(&ipSet, &rpcMdCfgDnodeMsg);
 
   mInfo("dnode:%s, is configured by %s", pCmCfgDnode->ep, pMsg->pUser->user);
+  dnodeSendMsgToDnode(&ipSet, &rpcMdCfgDnodeMsg);
 
   return TSDB_CODE_SUCCESS;
 }
@@ -305,6 +324,7 @@ static void mnodeProcessCfgDnodeMsgRsp(SRpcMsg *rpcMsg) {
 
 static bool mnodeCheckClusterCfgPara(const SClusterCfg *clusterCfg) {
   if (clusterCfg->numOfMnodes        != htonl(tsNumOfMnodes))        return false;
+  if (clusterCfg->enableBalance      != htonl(tsEnableBalance))        return false;
   if (clusterCfg->mnodeEqualVnodeNum != htonl(tsMnodeEqualVnodeNum)) return false;
   if (clusterCfg->offlineThreshold   != htonl(tsOfflineThreshold))   return false;
   if (clusterCfg->statusInterval     != htonl(tsStatusInterval))     return false;
diff --git a/src/mnode/src/mnodeVgroup.c b/src/mnode/src/mnodeVgroup.c
index 8b4d62a8b0711b7ddf44bc370f279df113a9e884..8c8aa5fb31977851b8928593639bd095f9cb9f55 100644
--- a/src/mnode/src/mnodeVgroup.c
+++ b/src/mnode/src/mnodeVgroup.c
@@ -593,7 +593,7 @@ static int32_t mnodeGetVgroupMeta(STableMetaMsg *pMeta, SShowObj *pShow, void *p
 
   pShow->bytes[cols] = 4;
   pSchema[cols].type = TSDB_DATA_TYPE_INT;
-  strcpy(pSchema[cols].name, "maxTables");
+  strcpy(pSchema[cols].name, "onlineVnodes");
   pSchema[cols].bytes = htons(pShow->bytes[cols]);
   cols++;
 
@@ -692,8 +692,15 @@ static int32_t mnodeRetrieveVgroups(SShowObj *pShow, char *data, int32_t rows, v
     *(int32_t *)pWrite = taosIdPoolMaxSize(pVgroup->idPool);
     cols++;
 
+    int32_t onlineVnodes = 0;
+    for (int32_t i = 0; i < pShow->maxReplica; ++i) {
+      if (pVgroup->vnodeGid[i].role == TAOS_SYNC_ROLE_SLAVE || pVgroup->vnodeGid[i].role == TAOS_SYNC_ROLE_MASTER) {
+        onlineVnodes++;
+      }
+    }
+
     pWrite = data + pShow->offset[cols] * rows + pShow->bytes[cols] * numOfRows;
-    *(int32_t *)pWrite = tsMaxTablePerVnode;
+    *(int32_t *)pWrite = onlineVnodes;
     cols++;
 
     for (int32_t i = 0; i < pShow->maxReplica; ++i) {
diff --git a/src/tsdb/src/tsdbMain.c b/src/tsdb/src/tsdbMain.c
index 6b3160070514b13d8b3b961854346d98d2b400a3..ffaab375a3bfc305cbedecae6df8881e28772aa2 100644
--- a/src/tsdb/src/tsdbMain.c
+++ b/src/tsdb/src/tsdbMain.c
@@ -69,6 +69,8 @@ static int         tsdbEncodeCfg(void **buf, STsdbCfg *pCfg);
 static void *      tsdbDecodeCfg(void *buf, STsdbCfg *pCfg);
 static int         tsdbCheckTableSchema(STsdbRepo *pRepo, SSubmitBlk *pBlock, STable *pTable);
 static int         tsdbScanAndConvertSubmitMsg(STsdbRepo *pRepo, SSubmitMsg *pMsg);
+static void        tsdbStartStream(STsdbRepo *pRepo);
+static void        tsdbStopStream(STsdbRepo *pRepo);
 
 // Function declaration
 int32_t tsdbCreateRepo(char *rootDir, STsdbCfg *pCfg) {
@@ -127,6 +129,7 @@ TSDB_REPO_T *tsdbOpenRepo(char *rootDir, STsdbAppH *pAppH) {
     goto _err;
   }
 
+  tsdbStartStream(pRepo);
   // pRepo->state = TSDB_REPO_STATE_ACTIVE;
 
   tsdbDebug("vgId:%d open tsdb repository succeed!", REPO_ID(pRepo));
@@ -145,6 +148,8 @@ void tsdbCloseRepo(TSDB_REPO_T *repo, int toCommit) {
   STsdbRepo *pRepo = (STsdbRepo *)repo;
   int        vgId = REPO_ID(pRepo);
 
+  tsdbStopStream(repo);
+
   if (toCommit) {
     tsdbAsyncCommit(pRepo);
     if (pRepo->commit) pthread_join(pRepo->commitThread, NULL);
@@ -265,19 +270,6 @@ uint32_t tsdbGetFileInfo(TSDB_REPO_T *repo, char *name, uint32_t *index, uint32_
   return magic;
 }
 
-void tsdbStartStream(TSDB_REPO_T *repo) {
-  STsdbRepo *pRepo = (STsdbRepo *)repo;
-  STsdbMeta *pMeta = pRepo->tsdbMeta;
-
-  for (int i = 0; i < pRepo->config.maxTables; i++) {
-    STable *pTable = pMeta->tables[i];
-    if (pTable && pTable->type == TSDB_STREAM_TABLE) {
-      pTable->cqhandle = (*pRepo->appH.cqCreateFunc)(pRepo->appH.cqH, TABLE_UID(pTable), TABLE_TID(pTable), pTable->sql,
-                                                     tsdbGetTableSchemaImpl(pTable, false, false, -1));
-    }
-  }
-}
-
 STsdbCfg *tsdbGetCfg(const TSDB_REPO_T *repo) {
   ASSERT(repo != NULL);
   return &((STsdbRepo *)repo)->config;
@@ -1120,4 +1112,27 @@ TSKEY tsdbGetTableLastKey(TSDB_REPO_T *repo, uint64_t uid) {
   return TSDB_GET_TABLE_LAST_KEY(pTable);
 }
 
-#endif
\ No newline at end of file
+#endif
+
+static void tsdbStartStream(STsdbRepo *pRepo) {
+  STsdbMeta *pMeta = pRepo->tsdbMeta;
+
+  for (int i = 0; i < pRepo->config.maxTables; i++) {
+    STable *pTable = pMeta->tables[i];
+    if (pTable && pTable->type == TSDB_STREAM_TABLE) {
+      pTable->cqhandle = (*pRepo->appH.cqCreateFunc)(pRepo->appH.cqH, TABLE_UID(pTable), TABLE_TID(pTable), pTable->sql,
+                                                     tsdbGetTableSchemaImpl(pTable, false, false, -1));
+    }
+  }
+}
+
+static void tsdbStopStream(STsdbRepo *pRepo) {
+  STsdbMeta *pMeta = pRepo->tsdbMeta;
+
+  for (int i = 0; i < pRepo->config.maxTables; i++) {
+    STable *pTable = pMeta->tables[i];
+    if (pTable && pTable->type == TSDB_STREAM_TABLE) {
+      (*pRepo->appH.cqDropFunc)(pTable->cqhandle);
+    }
+  }
+}
diff --git a/src/util/inc/tutil.h b/src/util/inc/tutil.h
index 1ba57bbaaa670cbd9aca7b19252a3bd745187130..f7c69e3973ad6fdefd4ef33f4a813221eedebe6d 100644
--- a/src/util/inc/tutil.h
+++ b/src/util/inc/tutil.h
@@ -133,6 +133,8 @@ char **strsplit(char *src, const char *delim, int32_t *num);
 
 char* strtolower(char *dst, const char *src);
 
+char* strntolower(char *dst, const char *src, int32_t n);
+
 int64_t strnatoi(char *num, int32_t len);
 
 //char* strreplace(const char* str, const char* pattern, const char* rep);
diff --git a/src/util/src/tsocket.c b/src/util/src/tsocket.c
index b225dfa36a4572ff3f56649e22ffdc81879d4d3c..5de61a3d57a0cc480781ec581bdc76d54419bf87 100644
--- a/src/util/src/tsocket.c
+++ b/src/util/src/tsocket.c
@@ -270,6 +270,14 @@ int taosOpenTcpClientSocket(uint32_t destIp, uint16_t destPort, uint32_t clientI
     return -1;
   }
 
+  /* set REUSEADDR option, so the portnumber can be re-used */
+  int reuse = 1;
+  if (taosSetSockOpt(sockFd, SOL_SOCKET, SO_REUSEADDR, (void *)&reuse, sizeof(reuse)) < 0) {
+    uError("setsockopt SO_REUSEADDR failed: %d (%s)", errno, strerror(errno));
+    close(sockFd);
+    return -1;
+  };
+
   if ( clientIp != 0) {
     memset((char *)&clientAddr, 0, sizeof(clientAddr));
     clientAddr.sin_family = AF_INET;
diff --git a/src/util/src/tutil.c b/src/util/src/tutil.c
index 1a74359f47af23d0073f41901f86282e3654e212..c8df34e1cd4e71954bf9255cc1507b5bb82d519b 100644
--- a/src/util/src/tutil.c
+++ b/src/util/src/tutil.c
@@ -234,6 +234,32 @@ char* strtolower(char *dst, const char *src) {
   *p = 0;
   return dst;
 }
+char* strntolower(char *dst, const char *src, int32_t n) {
+  int esc = 0;
+  char quote = 0, *p = dst, c;
+
+  assert(dst != NULL);
+
+  for (c = *src++; n-- > 0; c = *src++) {
+    if (esc) {
+      esc = 0;
+    } else if (quote) {
+      if (c == '\\') {
+        esc = 1;
+      } else if (c == quote) {
+        quote = 0;
+      }
+    } else if (c >= 'A' && c <= 'Z') {
+      c -= 'A' - 'a';
+    } else if (c == '\'' || c == '"') {
+      quote = c;
+    }
+    *p++ = c;
+  }
+
+  *p = 0;
+  return dst;
+}
 
 char *paGetToken(char *string, char **token, int32_t *tokenLen) {
   char quote = 0;
diff --git a/src/vnode/inc/vnodeInt.h b/src/vnode/inc/vnodeInt.h
index 77db4fd04c0f18569aec21bd459b4342a6ab568c..74cfbf1e731fd67c47f7375198a8353740429060 100644
--- a/src/vnode/inc/vnodeInt.h
+++ b/src/vnode/inc/vnodeInt.h
@@ -37,7 +37,7 @@ extern int32_t vDebugFlag;
 typedef struct {
   int32_t      vgId;      // global vnode group ID
   int32_t      refCount;  // reference count
-  int          status; 
+  int8_t       status; 
   int8_t       role;   
   int8_t       accessState;
   int64_t      version;   // current version 
@@ -55,6 +55,8 @@ typedef struct {
   SWalCfg      walCfg;
   void        *qMgmt;
   char        *rootDir;
+  tsem_t       sem;
+  int8_t       dropped;
   char         db[TSDB_DB_NAME_LEN];
 } SVnodeObj;
 
diff --git a/src/vnode/src/vnodeMain.c b/src/vnode/src/vnodeMain.c
index f316efcfdb2fda0426c47abb89801e35c713b82e..98882e4c3ccb4c1d964f41137b438f74c193853f 100644
--- a/src/vnode/src/vnodeMain.c
+++ b/src/vnode/src/vnodeMain.c
@@ -44,7 +44,7 @@ static int      vnodeProcessTsdbStatus(void *arg, int status);
 static uint32_t vnodeGetFileInfo(void *ahandle, char *name, uint32_t *index, uint32_t eindex, int32_t *size, uint64_t *fversion);
 static int      vnodeGetWalInfo(void *ahandle, char *name, uint32_t *index);
 static void     vnodeNotifyRole(void *ahandle, int8_t role);
-static void     vnodeNotifyFileSynced(void *ahandle, uint64_t fversion);
+static int      vnodeNotifyFileSynced(void *ahandle, uint64_t fversion);
 
 #ifndef _SYNC
 tsync_h syncStart(const SSyncInfo *info) { return NULL; }
@@ -153,7 +153,7 @@ int32_t vnodeDrop(int32_t vgId) {
 
   SVnodeObj *pVnode = *ppVnode;
   vTrace("vgId:%d, vnode will be dropped, refCount:%d", pVnode->vgId, pVnode->refCount);
-  pVnode->status = TAOS_VN_STATUS_DELETING;
+  pVnode->dropped = 1;
   vnodeCleanUp(pVnode);
 
   return TSDB_CODE_SUCCESS;
@@ -164,18 +164,11 @@ int32_t vnodeAlter(void *param, SMDCreateVnodeMsg *pVnodeCfg) {
 
   // vnode in non-ready state and still needs to return success instead of TSDB_CODE_VND_INVALID_STATUS
   // cfgVersion can be corrected by status msg
-  if (pVnode->status != TAOS_VN_STATUS_READY) {
+  if (atomic_val_compare_exchange_8(&pVnode->status, TAOS_VN_STATUS_READY, TAOS_VN_STATUS_UPDATING) != TAOS_VN_STATUS_READY) {
     vDebug("vgId:%d, vnode is not ready, do alter operation later", pVnode->vgId);
     return TSDB_CODE_SUCCESS;
   }
 
-  // the vnode may always fail to synchronize because of it in low cfgVersion
-  // so cannot use the following codes
-  // if (pVnode->syncCfg.replica > 1 && pVnode->role == TAOS_SYNC_ROLE_UNSYNCED) 
-  //   return TSDB_CODE_VND_NOT_SYNCED;
-
-  pVnode->status = TAOS_VN_STATUS_UPDATING;
-
   int32_t code = vnodeSaveCfg(pVnodeCfg);
   if (code != TSDB_CODE_SUCCESS) {
     pVnode->status = TAOS_VN_STATUS_READY;
@@ -194,10 +187,12 @@ int32_t vnodeAlter(void *param, SMDCreateVnodeMsg *pVnodeCfg) {
     return code; 
   } 
 
-  code = tsdbConfigRepo(pVnode->tsdb, &pVnode->tsdbCfg);
-  if (code != TSDB_CODE_SUCCESS) {
-    pVnode->status = TAOS_VN_STATUS_READY;
-    return code; 
+  if (pVnode->tsdb) {
+    code = tsdbConfigRepo(pVnode->tsdb, &pVnode->tsdbCfg);
+    if (code != TSDB_CODE_SUCCESS) {
+      pVnode->status = TAOS_VN_STATUS_READY;
+      return code; 
+    }
   }
 
   pVnode->status = TAOS_VN_STATUS_READY;
@@ -223,6 +218,7 @@ int32_t vnodeOpen(int32_t vnode, char *rootDir) {
   pVnode->tsdbCfg.tsdbId = pVnode->vgId;
   pVnode->rootDir = strdup(rootDir);
   pVnode->accessState = TSDB_VN_ALL_ACCCESS;
+  tsem_init(&pVnode->sem, 0, 0);
 
   int32_t code = vnodeReadCfg(pVnode);
   if (code != TSDB_CODE_SUCCESS) {
@@ -302,10 +298,6 @@ int32_t vnodeOpen(int32_t vnode, char *rootDir) {
   }
 #endif
 
-  // start continuous query
-  if (pVnode->role == TAOS_SYNC_ROLE_MASTER)
-    cqStart(pVnode->cq);
-
   pVnode->qMgmt = qOpenQueryMgmt(pVnode->vgId);
   pVnode->events = NULL;
   pVnode->status = TAOS_VN_STATUS_READY;
@@ -316,22 +308,12 @@ int32_t vnodeOpen(int32_t vnode, char *rootDir) {
   return TSDB_CODE_SUCCESS;
 }
 
-int32_t vnodeStartStream(int32_t vnode) {
-  SVnodeObj* pVnode = vnodeAcquireVnode(vnode);
-  if (pVnode != NULL) {
-    tsdbStartStream(pVnode->tsdb);
-    vnodeRelease(pVnode);
-  }
-  return TSDB_CODE_SUCCESS;
-}
-
 int32_t vnodeClose(int32_t vgId) {
   SVnodeObj **ppVnode = (SVnodeObj **)taosHashGet(tsDnodeVnodesHash, (const char *)&vgId, sizeof(int32_t));
   if (ppVnode == NULL || *ppVnode == NULL) return 0;
 
   SVnodeObj *pVnode = *ppVnode;
   vDebug("vgId:%d, vnode will be closed", pVnode->vgId);
-  pVnode->status = TAOS_VN_STATUS_CLOSING;
   vnodeCleanUp(pVnode);
 
   return 0;
@@ -346,6 +328,8 @@ void vnodeRelease(void *pVnodeRaw) {
 
   if (refCount > 0) {
     vDebug("vgId:%d, release vnode, refCount:%d", vgId, refCount);
+    if (pVnode->status == TAOS_VN_STATUS_RESET && refCount == 2) 
+      tsem_post(&pVnode->sem);
     return;
   }
 
@@ -356,11 +340,6 @@ void vnodeRelease(void *pVnodeRaw) {
     tsdbCloseRepo(pVnode->tsdb, 1);
   pVnode->tsdb = NULL;
 
-  // stop continuous query
-  if (pVnode->cq) 
-    cqClose(pVnode->cq);
-  pVnode->cq = NULL;
-
   if (pVnode->wal) 
     walClose(pVnode->wal);
   pVnode->wal = NULL;
@@ -375,20 +354,21 @@ void vnodeRelease(void *pVnodeRaw) {
  
   tfree(pVnode->rootDir);
 
-  if (pVnode->status == TAOS_VN_STATUS_DELETING) {
+  if (pVnode->dropped) {
     char rootDir[TSDB_FILENAME_LEN] = {0};
     sprintf(rootDir, "%s/vnode%d", tsVnodeDir, vgId);
     taosMvDir(tsVnodeBakDir, rootDir);
     taosRemoveDir(rootDir);
   }
 
+  tsem_destroy(&pVnode->sem);
   free(pVnode);
 
   int32_t count = taosHashGetSize(tsDnodeVnodesHash);
   vDebug("vgId:%d, vnode is released, vnodes:%d", vgId, count);
 }
 
-void *vnodeGetVnode(int32_t vgId) {
+void *vnodeAcquire(int32_t vgId) {
   SVnodeObj **ppVnode = (SVnodeObj **)taosHashGet(tsDnodeVnodesHash, (const char *)&vgId, sizeof(int32_t));
   if (ppVnode == NULL || *ppVnode == NULL) {
     terrno = TSDB_CODE_VND_INVALID_VGROUP_ID;
@@ -396,35 +376,38 @@ void *vnodeGetVnode(int32_t vgId) {
     return NULL;
   }
 
-  return *ppVnode;
-}
-
-void *vnodeAcquireVnode(int32_t vgId) {
-  SVnodeObj *pVnode = vnodeGetVnode(vgId);
-  if (pVnode == NULL) return pVnode;
-
+  SVnodeObj *pVnode = *ppVnode;
   atomic_add_fetch_32(&pVnode->refCount, 1);
   vDebug("vgId:%d, get vnode, refCount:%d", pVnode->vgId, pVnode->refCount);
 
   return pVnode;
 }
 
-void *vnodeAcquireRqueue(void *param) {
-  SVnodeObj *pVnode = param;
+void *vnodeAcquireRqueue(int32_t vgId) {
+  SVnodeObj *pVnode = vnodeAcquire(vgId);
   if (pVnode == NULL) return NULL;
 
-  atomic_add_fetch_32(&pVnode->refCount, 1);
-  vDebug("vgId:%d, get vnode rqueue, refCount:%d", pVnode->vgId, pVnode->refCount);
-  return ((SVnodeObj *)pVnode)->rqueue;
-}
+  if (pVnode->status == TAOS_VN_STATUS_RESET) {           
+    terrno = TSDB_CODE_VND_INVALID_STATUS;
+    vInfo("vgId:%d, status is in reset", vgId);
+    vnodeRelease(pVnode);
+    return NULL;
+  }
 
-void *vnodeGetRqueue(void *pVnode) {
-  return ((SVnodeObj *)pVnode)->rqueue;
+  return pVnode->rqueue;
 }
 
-void *vnodeGetWqueue(int32_t vgId) {
-  SVnodeObj *pVnode = vnodeAcquireVnode(vgId);
+void *vnodeAcquireWqueue(int32_t vgId) {
+  SVnodeObj *pVnode = vnodeAcquire(vgId);
   if (pVnode == NULL) return NULL;
+
+  if (pVnode->status == TAOS_VN_STATUS_RESET) {           
+    terrno = TSDB_CODE_VND_INVALID_STATUS;
+    vInfo("vgId:%d, status is in reset", vgId);
+    vnodeRelease(pVnode);
+    return NULL;
+  }
+  
   return pVnode->wqueue;
 }
 
@@ -496,7 +479,7 @@ void vnodeBuildStatusMsg(void *param) {
 void vnodeSetAccess(SDMVgroupAccess *pAccess, int32_t numOfVnodes) {
   for (int32_t i = 0; i < numOfVnodes; ++i) {
     pAccess[i].vgId = htonl(pAccess[i].vgId);
-    SVnodeObj *pVnode = vnodeAcquireVnode(pAccess[i].vgId);
+    SVnodeObj *pVnode = vnodeAcquire(pAccess[i].vgId);
     if (pVnode != NULL) {
       pVnode->accessState = pAccess[i].accessState;
       if (pVnode->accessState != TSDB_VN_ALL_ACCCESS) {
@@ -510,11 +493,29 @@ void vnodeSetAccess(SDMVgroupAccess *pAccess, int32_t numOfVnodes) {
 static void vnodeCleanUp(SVnodeObj *pVnode) {
   // remove from hash, so new messages wont be consumed
   taosHashRemove(tsDnodeVnodesHash, (const char *)&pVnode->vgId, sizeof(int32_t));
+  int i = 0;
+
+  if (pVnode->status != TAOS_VN_STATUS_INIT) {
+    // it may be in updateing or reset state, then it shall wait
+    while (atomic_val_compare_exchange_8(&pVnode->status, TAOS_VN_STATUS_READY, TAOS_VN_STATUS_CLOSING) != TAOS_VN_STATUS_READY) {
+      if (++i % 1000 == 0) {
+        sched_yield();
+      }
+    }
+  }
 
   // stop replication module
   if (pVnode->sync) {
-    syncStop(pVnode->sync);
+    void *sync = pVnode->sync;
     pVnode->sync = NULL;
+    syncStop(sync);
+  }
+
+  // stop continuous query
+  if (pVnode->cq) {
+    void *cq = pVnode->cq;
+    pVnode->cq = NULL;
+    cqClose(cq);
   }
 
   vTrace("vgId:%d, vnode will cleanup, refCount:%d", pVnode->vgId, pVnode->refCount);
@@ -561,18 +562,25 @@ static void vnodeNotifyRole(void *ahandle, int8_t role) {
     cqStop(pVnode->cq);
 }
 
-static void vnodeNotifyFileSynced(void *ahandle, uint64_t fversion) {
-  SVnodeObj *pVnode = ahandle;
-  vDebug("vgId:%d, data file is synced, fversion:%" PRId64, pVnode->vgId, fversion);
-
-  pVnode->fversion = fversion;
-  pVnode->version = fversion;
-  vnodeSaveVersion(pVnode);
-
+static int vnodeResetTsdb(SVnodeObj *pVnode)
+{
   char rootDir[128] = "\0";
   sprintf(rootDir, "%s/tsdb", pVnode->rootDir);
-  // clsoe tsdb, then open tsdb
-  tsdbCloseRepo(pVnode->tsdb, 0);
+
+  if (atomic_val_compare_exchange_8(&pVnode->status, TAOS_VN_STATUS_READY, TAOS_VN_STATUS_RESET) != TAOS_VN_STATUS_READY)
+    return -1;
+
+  void *tsdb = pVnode->tsdb;
+  pVnode->tsdb = NULL;
+
+  // acquire vnode
+  int32_t refCount = atomic_add_fetch_32(&pVnode->refCount, 1); 
+
+  if (refCount > 2) 
+    tsem_wait(&pVnode->sem);
+
+  // close tsdb, then open tsdb
+  tsdbCloseRepo(tsdb, 0);
   STsdbAppH appH = {0};
   appH.appH = (void *)pVnode;
   appH.notifyStatus = vnodeProcessTsdbStatus;
@@ -580,6 +588,22 @@ static void vnodeNotifyFileSynced(void *ahandle, uint64_t fversion) {
   appH.cqCreateFunc = cqCreate;
   appH.cqDropFunc = cqDrop;
   pVnode->tsdb = tsdbOpenRepo(rootDir, &appH);
+
+  pVnode->status = TAOS_VN_STATUS_READY;
+  vnodeRelease(pVnode);  
+
+  return 0;
+}
+
+static int vnodeNotifyFileSynced(void *ahandle, uint64_t fversion) {
+  SVnodeObj *pVnode = ahandle;
+  vDebug("vgId:%d, data file is synced, fversion:%" PRId64, pVnode->vgId, fversion);
+
+  pVnode->fversion = fversion;
+  pVnode->version = fversion;
+  vnodeSaveVersion(pVnode);
+
+  return vnodeResetTsdb(pVnode);
 }
 
 static int32_t vnodeSaveCfg(SMDCreateVnodeMsg *pVnodeCfg) {
diff --git a/src/vnode/src/vnodeRead.c b/src/vnode/src/vnodeRead.c
index f529b713cf659d923e64ba8bf49798a0dde0f195..973df7c5a10f2ba84a77718602c8ffddd4b14134 100644
--- a/src/vnode/src/vnodeRead.c
+++ b/src/vnode/src/vnodeRead.c
@@ -26,6 +26,7 @@
 #include "tsdb.h"
 #include "vnode.h"
 #include "vnodeInt.h"
+#include "tqueue.h"
 
 static int32_t (*vnodeProcessReadMsgFp[TSDB_MSG_TYPE_MAX])(SVnodeObj *pVnode, SReadMsg *pReadMsg);
 static int32_t  vnodeProcessQueryMsg(SVnodeObj *pVnode, SReadMsg *pReadMsg);
@@ -51,6 +52,11 @@ int32_t vnodeProcessRead(void *param, SReadMsg *pReadMsg) {
     return TSDB_CODE_VND_INVALID_STATUS; 
   }
 
+  // tsdb may be in reset state  
+  if (pVnode->tsdb == NULL) return TSDB_CODE_RPC_NOT_READY;
+  if (pVnode->status == TAOS_VN_STATUS_CLOSING)
+    return TSDB_CODE_RPC_NOT_READY;
+
   // TODO: Later, let slave to support query
   if (pVnode->syncCfg.replica > 1 && pVnode->role != TAOS_SYNC_ROLE_MASTER) {
     vDebug("vgId:%d, msgType:%s not processed, replica:%d role:%d", pVnode->vgId, taosMsg[msgType], pVnode->syncCfg.replica, pVnode->role);
@@ -60,6 +66,16 @@ int32_t vnodeProcessRead(void *param, SReadMsg *pReadMsg) {
   return (*vnodeProcessReadMsgFp[msgType])(pVnode, pReadMsg);
 }
 
+static void vnodePutItemIntoReadQueue(SVnodeObj *pVnode, void *qhandle) {
+  SReadMsg *pRead = (SReadMsg *)taosAllocateQitem(sizeof(SReadMsg));
+  pRead->rpcMsg.msgType = TSDB_MSG_TYPE_QUERY;
+  pRead->pCont = qhandle;
+  pRead->contLen = 0;
+
+  atomic_add_fetch_32(&pVnode->refCount, 1);
+  taosWriteQitem(pVnode->rqueue, TAOS_QTYPE_QUERY, pRead);
+}
+
 static int32_t vnodeProcessQueryMsg(SVnodeObj *pVnode, SReadMsg *pReadMsg) {
   void    *pCont = pReadMsg->pCont;
   int32_t  contLen = pReadMsg->contLen;
@@ -131,7 +147,7 @@ static int32_t vnodeProcessQueryMsg(SVnodeObj *pVnode, SReadMsg *pReadMsg) {
     if (handle != NULL) {
       vDebug("vgId:%d, QInfo:%p, dnode query msg disposed, register qhandle and return to app", vgId, *handle);
 
-      dnodePutItemIntoReadQueue(pVnode, *handle);
+      vnodePutItemIntoReadQueue(pVnode, *handle);
       qReleaseQInfo(pVnode->qMgmt, (void**) &handle, false);
     }
 
@@ -208,7 +224,7 @@ static int32_t vnodeProcessFetchMsg(SVnodeObj *pVnode, SReadMsg *pReadMsg) {
   } else { // if failed to dump result, free qhandle immediately
     if ((code = qDumpRetrieveResult(*handle, (SRetrieveTableRsp **)&pRet->rsp, &pRet->len)) == TSDB_CODE_SUCCESS) {
       if (qHasMoreResultsToRetrieve(*handle)) {
-        dnodePutItemIntoReadQueue(pVnode, *handle);
+        vnodePutItemIntoReadQueue(pVnode, *handle);
         pRet->qhandle = *handle;
         freeHandle = false;
       } else {
diff --git a/src/vnode/src/vnodeWrite.c b/src/vnode/src/vnodeWrite.c
index 09e4b43ed38091247da0a51a56a41c52f2bb010e..6b9b8ca4fd5a5c42028936e48b53f45ffa811903 100644
--- a/src/vnode/src/vnodeWrite.c
+++ b/src/vnode/src/vnodeWrite.c
@@ -59,13 +59,18 @@ int32_t vnodeProcessWrite(void *param1, int qtype, void *param2, void *item) {
     return TSDB_CODE_VND_NO_WRITE_AUTH;
   }
 
+  // tsdb may be in reset state 
+  if (pVnode->tsdb == NULL) return TSDB_CODE_RPC_NOT_READY;
+  if (pVnode->status == TAOS_VN_STATUS_CLOSING) 
+    return TSDB_CODE_RPC_NOT_READY;
+  
   if (pHead->version == 0) { // from client or CQ 
     if (pVnode->status != TAOS_VN_STATUS_READY) {
       vDebug("vgId:%d, msgType:%s not processed, vnode status is %d", pVnode->vgId, taosMsg[pHead->msgType], pVnode->status);
       return TSDB_CODE_VND_INVALID_STATUS;  // it may be in deleting or closing state
     }
 
-    if (pVnode->syncCfg.replica > 1 && pVnode->role != TAOS_SYNC_ROLE_MASTER) {
+    if (pVnode->role != TAOS_SYNC_ROLE_MASTER) {
       vDebug("vgId:%d, msgType:%s not processed, replica:%d role:%d", pVnode->vgId, taosMsg[pHead->msgType], pVnode->syncCfg.replica, pVnode->role);
       return TSDB_CODE_RPC_NOT_READY;
     }
diff --git a/tests/pytest/fulltest.sh b/tests/pytest/fulltest.sh
index 5ee33c421ea1a2da6949d057f6670353a09abd3d..9d1aef0dc5cc2cf266931ff6e8ba88794649686c 100755
--- a/tests/pytest/fulltest.sh
+++ b/tests/pytest/fulltest.sh
@@ -143,6 +143,7 @@ python3 ./test.py -f query/filterOtherTypes.py
 python3 ./test.py -f query/querySort.py
 python3 ./test.py -f query/queryJoin.py
 python3 ./test.py -f query/select_last_crash.py
+python3 ./test.py -f query/queryNullValueTest.py
 
 #stream
 python3 ./test.py -f stream/metric_1.py
diff --git a/tests/pytest/query/queryInsertValue.py b/tests/pytest/query/queryInsertValue.py
new file mode 100644
index 0000000000000000000000000000000000000000..856801b4ee162a35e1e4e4b864860180960a1432
--- /dev/null
+++ b/tests/pytest/query/queryInsertValue.py
@@ -0,0 +1,65 @@
+###################################################################
+#           Copyright (c) 2016 by TAOS Technologies, Inc.
+#                     All rights reserved.
+#
+#  This file is proprietary and confidential to TAOS Technologies.
+#  No part of this file may be reproduced, stored, transmitted,
+#  disclosed or used in any form or by any means other than as
+#  expressly provided by the written permission from Jianhui Tao
+#
+###################################################################
+
+# -*- coding: utf-8 -*-
+
+import sys
+import taos
+from util.log import *
+from util.cases import *
+from util.sql import *
+import numpy as np
+from util.dnodes import *
+
+
+class TDTestCase:
+    def init(self, conn, logSql):
+        tdLog.debug("start to execute %s" % __file__)
+        tdSql.init(conn.cursor(), logSql)
+        
+        self.numOfRecords = 10
+        self.ts = 1537146000000    
+    
+    def restartTaosd(self):
+        tdDnodes.stop(1)
+        tdDnodes.start(1)
+        tdSql.execute("use db")
+
+    def run(self):
+        tdSql.prepare()
+
+        print("==============step1")
+
+        tdSql.execute(
+            "create table st (ts timestamp, speed int) tags(areaid int, loc nchar(20))")
+        tdSql.execute("create table t1 using st tags(1, 'beijing')")
+        tdSql.execute("insert into t1 values(now, 1)")
+        tdSql.query("select * from st")
+        tdSql.checkRows(1)
+
+        tdSql.execute("alter table st add column length int")
+        tdSql.execute("insert into t1 values(now, 1, 2)")
+        tdSql.query("select last(*) from st")
+        tdSql.checkData(0, 2, 2);
+
+        self.restartTaosd();
+
+        tdSql.query("select last(*) from st")
+        tdSql.checkData(0, 2, 2);
+
+
+    def stop(self):
+        tdSql.close()
+        tdLog.success("%s successfully executed" % __file__)
+
+
+tdCases.addWindows(__file__, TDTestCase())
+tdCases.addLinux(__file__, TDTestCase())
diff --git a/tests/pytest/query/queryNullValueTest.py b/tests/pytest/query/queryNullValueTest.py
new file mode 100644
index 0000000000000000000000000000000000000000..2ad1979e0bfb33246d087e85132341fdc6e0bdcd
--- /dev/null
+++ b/tests/pytest/query/queryNullValueTest.py
@@ -0,0 +1,181 @@
+###################################################################
+#           Copyright (c) 2016 by TAOS Technologies, Inc.
+#                     All rights reserved.
+#
+#  This file is proprietary and confidential to TAOS Technologies.
+#  No part of this file may be reproduced, stored, transmitted,
+#  disclosed or used in any form or by any means other than as
+#  expressly provided by the written permission from Jianhui Tao
+#
+###################################################################
+
+# -*- coding: utf-8 -*-
+
+import sys
+import taos
+from util.log import *
+from util.cases import *
+from util.sql import *
+import numpy as np
+from util.dnodes import *
+
+
+class TDTestCase:
+    def init(self, conn, logSql):
+        tdLog.debug("start to execute %s" % __file__)
+        tdSql.init(conn.cursor(), logSql)
+        
+        self.numOfRecords = 10
+        self.ts = 1537146000000
+
+    def checkNullValue(self, result):
+        mx = np.array(result)
+        [rows, cols] = mx.shape
+        for i in range(rows):
+            for j in range(cols):
+                if j + 1 < cols and mx[i, j + 1] is not None:
+                    print(mx[i, j + 1])
+                    return False
+        return True
+    
+    def restartTaosd(self):
+        tdDnodes.stop(1)
+        tdDnodes.start(1)
+        tdSql.execute("use db")
+
+    def run(self):
+        tdSql.prepare()
+
+        print("==============step1")
+
+        tdSql.execute(
+            "create table meters (ts timestamp, col1 int) tags(tgcol1 int)")
+        tdSql.execute("create table t0 using meters tags(NULL)")
+
+        for i in range (self.numOfRecords):
+            tdSql.execute("insert into t0 values (%d, %d)" % (self.ts + i, i));
+
+        tdSql.query("select * from meters")
+        tdSql.checkRows(10)
+
+        tdSql.execute("alter table meters add column col2 tinyint")
+        tdSql.execute("alter table meters drop column col1")        
+        tdSql.query("select * from meters")        
+        tdSql.checkRows(10)
+        tdSql.query("select col2 from meters")        
+        tdSql.checkRows(10)        
+
+        tdSql.execute("alter table meters add column col1 int")
+        tdSql.query("select * from meters")
+        tdSql.checkRows(10)
+        tdSql.query("select col1 from meters")        
+        tdSql.checkRows(10)
+
+        tdSql.execute("alter table meters add column col3 smallint")
+        tdSql.query("select * from meters")
+        tdSql.checkRows(10)
+        tdSql.query("select col3 from meters")        
+        tdSql.checkRows(10)
+
+        tdSql.execute("alter table meters add column col4 bigint")
+        tdSql.query("select * from meters")
+        tdSql.checkRows(10)
+        tdSql.query("select col4 from meters")        
+        tdSql.checkRows(10)
+
+        tdSql.execute("alter table meters add column col5 float")
+        tdSql.query("select * from meters")
+        tdSql.checkRows(10)
+        tdSql.query("select col5 from meters")        
+        tdSql.checkRows(10)
+
+        tdSql.execute("alter table meters add column col6 double")
+        tdSql.query("select * from meters")
+        tdSql.checkRows(10)
+        tdSql.query("select col6 from meters")        
+        tdSql.checkRows(10)
+
+        tdSql.execute("alter table meters add column col7 bool")
+        tdSql.query("select * from meters")
+        tdSql.checkRows(10)
+        tdSql.query("select col7 from meters")        
+        tdSql.checkRows(10)
+
+        tdSql.execute("alter table meters add column col8 binary(20)")
+        tdSql.query("select * from meters")
+        tdSql.checkRows(10)
+        tdSql.query("select col8 from meters")        
+        tdSql.checkRows(10)
+
+        tdSql.execute("alter table meters add column col9 nchar(20)")
+        tdSql.query("select * from meters")
+        tdSql.checkRows(10)
+        tdSql.query("select col9 from meters")        
+        tdSql.checkRows(10)
+        
+        tdSql.execute("alter table meters add tag tgcol2 tinyint")
+        tdSql.query("select * from meters")
+        tdSql.checkRows(10)
+        tdSql.query("select tgcol2 from meters")
+        tdSql.checkRows(1)
+                
+
+        tdSql.execute("alter table meters add tag tgcol3 smallint")
+        tdSql.query("select * from meters")
+        tdSql.checkRows(10)
+        tdSql.query("select tgcol3 from meters")
+        tdSql.checkRows(1)
+        
+
+        tdSql.execute("alter table meters add tag tgcol4 bigint")
+        tdSql.query("select * from meters")
+        tdSql.checkRows(10)
+        tdSql.query("select tgcol4 from meters")
+        tdSql.checkRows(1)
+
+        tdSql.execute("alter table meters add tag tgcol5 float")
+        tdSql.query("select * from meters")
+        tdSql.checkRows(10)
+        tdSql.query("select tgcol5 from meters")
+        tdSql.checkRows(1)
+
+        tdSql.execute("alter table meters add tag tgcol6 double")
+        tdSql.query("select * from meters")
+        tdSql.checkRows(10)
+        tdSql.query("select tgcol6 from meters")
+        tdSql.checkRows(1)
+
+        tdSql.execute("alter table meters add tag tgcol7 bool")
+        tdSql.query("select * from meters")
+        tdSql.checkRows(10)
+        tdSql.query("select tgcol7 from meters")
+        tdSql.checkRows(1)
+
+        tdSql.execute("alter table meters add tag tgcol8 binary(20)")
+        tdSql.query("select * from meters")
+        tdSql.checkRows(10)
+        tdSql.query("select tgcol8 from meters")
+        tdSql.checkRows(1)
+
+        tdSql.execute("alter table meters add tag tgcol9 nchar(20)")
+        tdSql.query("select * from meters")
+        tdSql.checkRows(10)
+        tdSql.query("select tgcol9 from meters")
+        tdSql.checkRows(1)
+
+        self.restartTaosd()
+        tdSql.query("select * from meters")        
+        tdSql.checkRows(10)
+        if self.checkNullValue(tdSql.queryResult) is False:
+            tdLog.exit("non None value is detected")
+
+
+        
+
+    def stop(self):
+        tdSql.close()
+        tdLog.success("%s successfully executed" % __file__)
+
+
+tdCases.addWindows(__file__, TDTestCase())
+tdCases.addLinux(__file__, TDTestCase())
diff --git a/tests/pytest/regressiontest.sh b/tests/pytest/regressiontest.sh
index ccc6635ced9dd532bb62149a00608ba5a849d04f..24cd93f0fc58772e2d1741d9ee0119d9d5247357 100755
--- a/tests/pytest/regressiontest.sh
+++ b/tests/pytest/regressiontest.sh
@@ -140,6 +140,7 @@ python3 ./test.py -f query/queryJoin.py
 python3 ./test.py -f query/filterCombo.py
 python3 ./test.py -f query/queryNormal.py
 python3 ./test.py -f query/select_last_crash.py
+python3 ./test.py -f query/queryNullValueTest.py
 
 #stream
 python3 ./test.py -f stream/stream1.py
diff --git a/tests/script/sh/deploy.sh b/tests/script/sh/deploy.sh
index 445baa9e45326e895d75489262217f9d3f938606..b9a9e4f02460717e04d4ba4f6347f9bab666207b 100755
--- a/tests/script/sh/deploy.sh
+++ b/tests/script/sh/deploy.sh
@@ -136,6 +136,8 @@ echo "defaultPass         taosdata"       >> $TAOS_CFG
 echo "numOfLogLines       20000000"       >> $TAOS_CFG
 echo "mnodeEqualVnodeNum  0"              >> $TAOS_CFG
 echo "clog                2"              >> $TAOS_CFG
+#echo "cache              1"              >> $TAOS_CFG
+#echo "block              2"              >> $TAOS_CFG
 echo "statusInterval      1"              >> $TAOS_CFG
 echo "numOfTotalVnodes    4"              >> $TAOS_CFG
 echo "maxVgroupsPerDb     4"              >> $TAOS_CFG
diff --git a/tests/script/sh/exec.sh b/tests/script/sh/exec.sh
index 6928039be11642b82e9a50d2f32a38d442abfbce..2f294075a1695298cb52b53bc52e11d9dce9fe07 100755
--- a/tests/script/sh/exec.sh
+++ b/tests/script/sh/exec.sh
@@ -88,7 +88,9 @@ if [ "$EXEC_OPTON" = "start" ]; then
   echo "ExcuteCmd:" $EXE_DIR/taosd -c $CFG_DIR
   
   if [ "$SHELL_OPTION" = "true" ]; then 
-    nohup valgrind --log-file=${LOG_DIR}/valgrind.log --tool=memcheck --leak-check=full --show-reachable=no  --track-origins=yes --show-leak-kinds=all  -v  --workaround-gcc296-bugs=yes   $EXE_DIR/taosd -c $CFG_DIR > /dev/null 2>&1 &   
+    TT=`date +%s`
+    mkdir ${LOG_DIR}/${TT}
+    nohup valgrind --log-file=${LOG_DIR}/${TT}/valgrind.log --tool=memcheck --leak-check=full --show-reachable=no  --track-origins=yes --show-leak-kinds=all  -v  --workaround-gcc296-bugs=yes   $EXE_DIR/taosd -c $CFG_DIR > /dev/null 2>&1 &   
   else
     nohup $EXE_DIR/taosd -c $CFG_DIR > /dev/null 2>&1 & 
   fi
diff --git a/tests/script/unique/vnode/replica2_a_large.sim b/tests/script/unique/vnode/replica2_a_large.sim
new file mode 100644
index 0000000000000000000000000000000000000000..801570dd9c18daa5611d621660e88905fa73c2b3
--- /dev/null
+++ b/tests/script/unique/vnode/replica2_a_large.sim
@@ -0,0 +1,103 @@
+system sh/stop_dnodes.sh
+
+system sh/deploy.sh -n dnode1 -i 1
+system sh/deploy.sh -n dnode2 -i 2
+system sh/deploy.sh -n dnode3 -i 3
+system sh/deploy.sh -n dnode4 -i 4
+system sh/cfg.sh -n dnode1 -c wallevel -v 2
+system sh/cfg.sh -n dnode2 -c wallevel -v 2
+system sh/cfg.sh -n dnode3 -c wallevel -v 2
+system sh/cfg.sh -n dnode4 -c wallevel -v 2
+system sh/cfg.sh -n dnode1 -c numOfMnodes -v 1
+system sh/cfg.sh -n dnode2 -c numOfMnodes -v 1
+system sh/cfg.sh -n dnode3 -c numOfMnodes -v 1
+system sh/cfg.sh -n dnode4 -c numOfMnodes -v 1
+system sh/cfg.sh -n dnode1 -c mnodeEqualVnodeNum -v 4
+system sh/cfg.sh -n dnode2 -c mnodeEqualVnodeNum -v 4
+system sh/cfg.sh -n dnode3 -c mnodeEqualVnodeNum -v 4
+system sh/cfg.sh -n dnode4 -c mnodeEqualVnodeNum -v 4
+system sh/cfg.sh -n dnode1 -c debugFlag -v 131
+system sh/cfg.sh -n dnode2 -c debugFlag -v 131
+system sh/cfg.sh -n dnode3 -c debugFlag -v 131
+system sh/cfg.sh -n dnode4 -c debugFlag -v 131
+system sh/cfg.sh -n dnode1 -c arbitrator -v $arbitrator
+system sh/cfg.sh -n dnode2 -c arbitrator -v $arbitrator
+system sh/cfg.sh -n dnode3 -c arbitrator -v $arbitrator
+system sh/cfg.sh -n dnode4 -c arbitrator -v $arbitrator
+
+print ============== step0: start tarbitrator
+system sh/exec_tarbitrator.sh -s start
+
+system sh/exec.sh -n dnode1 -s start
+sleep 3000
+sql connect
+
+sql create dnode $hostname2
+sql create dnode $hostname3
+system sh/exec.sh -n dnode2 -s start -t
+system sh/exec.sh -n dnode3 -s start -t
+sleep 3000
+
+print ========= step1
+sql create database db replica 2 
+#sql create table db.tb1 (ts timestamp, i int)
+#sql create table db.tb2 (ts timestamp, i int)
+#sql create table db.tb3 (ts timestamp, i int)
+#sql create table db.tb4 (ts timestamp, i int)
+#sql insert into db.tb1 values(now, 1)
+#sql select count(*) from db.tb1
+
+sql create database db replica 2 
+sql create table db.tb (ts timestamp, i int)
+sql insert into db.tb values(now, 1)
+sql select count(*) from db.tb
+$lastRows = $rows
+
+print ======== step2
+#run_back unique/vnode/back_insert_many.sim
+run_back unique/vnode/back_insert.sim
+sleep 3000
+
+print ======== step3
+
+$x = 0
+loop:
+
+print ======== step4
+system sh/exec.sh -n dnode2 -s stop -x SIGINT
+sleep 10000
+system sh/exec.sh -n dnode2 -s start -t
+sleep 10000
+
+print ======== step5
+system sh/exec.sh -n dnode3 -s stop -x SIGINT
+sleep 10000
+system sh/exec.sh -n dnode3 -s start -t
+sleep 10000
+
+print ======== step6
+#sql select count(*) from db.tb1
+#print select count(*) from db.tb1 ==> $data00 $lastRows 
+sql select count(*) from db.tb
+print select count(*) from db.tb ==> $data00 $lastRows 
+if $data00 <= $lastRows then
+  return -1
+endi
+
+print ======== step7
+$lastRows = $data00
+print ======== loop Times $x
+
+if $x < 10 then
+  $x = $x + 1
+  goto loop
+endi
+
+system sh/exec.sh -n dnode1 -s stop  -x SIGINT
+system sh/exec.sh -n dnode2 -s stop  -x SIGINT
+system sh/exec.sh -n dnode3 -s stop  -x SIGINT
+system sh/exec.sh -n dnode4 -s stop  -x SIGINT
+system sh/exec.sh -n dnode5 -s stop  -x SIGINT
+system sh/exec.sh -n dnode6 -s stop  -x SIGINT
+system sh/exec.sh -n dnode7 -s stop  -x SIGINT
+system sh/exec.sh -n dnode8 -s stop  -x SIGINT
\ No newline at end of file