diff --git a/src/client/src/tscServer.c b/src/client/src/tscServer.c
index 3f4e9864aaad..07aff292f831 100644
--- a/src/client/src/tscServer.c
+++ b/src/client/src/tscServer.c
@@ -460,13 +460,14 @@ int tscSendMsgToServer(SSqlObj *pSql) {
   }
 
 
-  if(rpcSendRequest(pObj->pRpcObj->pDnodeConn, &pSql->epSet, &rpcMsg, &pSql->rpcRid)) {
-    if(pSql->cmd.command < TSDB_SQL_HB)
+  if(rpcSendRequest(pObj->pRpcObj->pDnodeConn, &pSql->epSet, &rpcMsg, &pSql->rpcRid) != BOOL_FALSE) {
+    if(pSql->cmd.command == TSDB_SQL_SELECT)
       rpcSaveSendInfo(pSql->rpcRid, &pSql->pPrevContext);
     return TSDB_CODE_SUCCESS;
   }
 
-  return TSDB_CODE_SUCCESS;
+  tscError("0x%"PRIx64" rpc send data failed. msg=%s", pSql->self, taosMsg[pSql->cmd.msgType]);
+  return TSDB_CODE_TSC_SEND_DATA_FAILED;
 }
 
 // handle three situation
diff --git a/src/client/src/tscSubquery.c b/src/client/src/tscSubquery.c
index ab34d99bfc4b..09574e741fe7 100644
--- a/src/client/src/tscSubquery.c
+++ b/src/client/src/tscSubquery.c
@@ -3296,7 +3296,8 @@ void tscRetrieveDataRes(void *param, TAOS_RES *tres, int code) {
   // the param may be null, since it may be done by other query threads. and the asyncOnError may enter in this
   // function while kill query by a user.
   if (param == NULL) {
-    assert(code != TSDB_CODE_SUCCESS);
+    if(code != TSDB_CODE_SUCCESS)
+      tscError("tscRetrieveDataRes param is NULL, error code=%d", code);
     return;
   }
 
diff --git a/src/inc/taos.h b/src/inc/taos.h
index 5cb0420fe2e8..44d83969a809 100644
--- a/src/inc/taos.h
+++ b/src/inc/taos.h
@@ -48,6 +48,12 @@ typedef void **TAOS_ROW;
 #define TSDB_DATA_TYPE_UBIGINT    14    // 8 bytes
 #define TSDB_DATA_TYPE_JSON       15    // json string
 
+typedef enum {
+  BOOL_FALSE = 0,
+  BOOL_TRUE  = 1,
+  BOOL_ASYNC = 2  //request is processed by async for another thread, not now true or false
+} TBOOL;
+
 typedef enum {
   TSDB_OPTION_LOCALE,
   TSDB_OPTION_CHARSET,
diff --git a/src/inc/taoserror.h b/src/inc/taoserror.h
index 9f51952d28ab..fc387d331b07 100644
--- a/src/inc/taoserror.h
+++ b/src/inc/taoserror.h
@@ -118,6 +118,7 @@ int32_t* taosGetErrno();
 #define TSDB_CODE_TSC_RES_TOO_MANY              TAOS_DEF_ERROR_CODE(0, 0x0227)  //"Result set too large to be output")
 #define TSDB_CODE_TSC_INVALID_SCHEMA_VERSION    TAOS_DEF_ERROR_CODE(0, 0x0228)  //"invalid table schema version")
 #define TSDB_CODE_TSC_TOO_MANY_SML_LINES        TAOS_DEF_ERROR_CODE(0, 0x0229)  //"too many lines in batch")
+#define TSDB_CODE_TSC_SEND_DATA_FAILED          TAOS_DEF_ERROR_CODE(0, 0x0230)  //"Client send request data error"
 
 // mnode
 #define TSDB_CODE_MND_MSG_NOT_PROCESSED         TAOS_DEF_ERROR_CODE(0, 0x0300)  //"Message not processed"
diff --git a/src/inc/trpc.h b/src/inc/trpc.h
index db2978569993..fe061eb4f20f 100644
--- a/src/inc/trpc.h
+++ b/src/inc/trpc.h
@@ -85,7 +85,7 @@ void  rpcClose(void *);
 void *rpcMallocCont(int contLen);
 void  rpcFreeCont(void *pCont);
 void *rpcReallocCont(void *ptr, int contLen);
-bool  rpcSendRequest(void *thandle, const SRpcEpSet *pEpSet, SRpcMsg *pMsg, int64_t *rid);
+TBOOL rpcSendRequest(void *thandle, const SRpcEpSet *pEpSet, SRpcMsg *pMsg, int64_t *rid);
 void  rpcSendResponse(const SRpcMsg *pMsg);
 void  rpcSendRedirectRsp(void *pConn, const SRpcEpSet *pEpSet); 
 int   rpcGetConnInfo(void *thandle, SRpcConnInfo *pInfo);
diff --git a/src/rpc/src/rpcMain.c b/src/rpc/src/rpcMain.c
index dc69cb890557..6566bf9e79f3 100644
--- a/src/rpc/src/rpcMain.c
+++ b/src/rpc/src/rpcMain.c
@@ -202,7 +202,7 @@ static SRpcConn *rpcAllocateClientConn(SRpcInfo *pRpc);
 static SRpcConn *rpcAllocateServerConn(SRpcInfo *pRpc, SRecvInfo *pRecv);
 static SRpcConn *rpcGetConnObj(SRpcInfo *pRpc, int sid, SRecvInfo *pRecv);
 
-static bool  rpcSendReqToServer(SRpcInfo *pRpc, SRpcReqContext *pContext);
+static TBOOL rpcSendReqToServer(SRpcInfo *pRpc, SRpcReqContext *pContext);
 static void  rpcSendQuickRsp(SRpcConn *pConn, int32_t code);
 static void  rpcSendErrorMsgToPeer(SRecvInfo *pRecv, int32_t code);
 static bool  rpcSendMsgToPeer(SRpcConn *pConn, void *data, int dataLen);
@@ -394,7 +394,7 @@ void *rpcReallocCont(void *ptr, int contLen) {
   return start + sizeof(SRpcReqContext) + sizeof(SRpcHead);
 }
 
-bool rpcSendRequest(void *shandle, const SRpcEpSet *pEpSet, SRpcMsg *pMsg, int64_t *pRid) {
+TBOOL rpcSendRequest(void *shandle, const SRpcEpSet *pEpSet, SRpcMsg *pMsg, int64_t *pRid) {
   SRpcInfo       *pRpc = (SRpcInfo *)shandle;
   SRpcReqContext *pContext;
 
@@ -1384,7 +1384,7 @@ static void rpcSendErrorMsgToPeer(SRecvInfo *pRecv, int32_t code) {
   return; 
 }
 
-static bool rpcSendReqToServer(SRpcInfo *pRpc, SRpcReqContext *pContext) {
+static TBOOL rpcSendReqToServer(SRpcInfo *pRpc, SRpcReqContext *pContext) {
   SRpcHead  *pHead = rpcHeadFromCont(pContext->pCont);
   char      *msg = (char *)pHead;
   int        msgLen = rpcMsgLenFromCont(pContext->contLen);
@@ -1394,8 +1394,9 @@ static bool rpcSendReqToServer(SRpcInfo *pRpc, SRpcReqContext *pContext) {
   SRpcConn *pConn = rpcSetupConnToServer(pContext);
   if (pConn == NULL) {
     pContext->code = terrno;
+    // in rpcProcessConnError if numOfTry over limit, could call rpcNotifyClient to stop query
     taosTmrStart(rpcProcessConnError, 1, pContext, pRpc->tmrCtrl);
-    return false;
+    return BOOL_ASYNC;
   }
 
   pContext->pConn = pConn;
@@ -1436,7 +1437,16 @@ static bool rpcSendReqToServer(SRpcInfo *pRpc, SRpcReqContext *pContext) {
     taosTmrReset(rpcProcessRetryTimer, tsRpcTimer, pConn, pRpc->tmrCtrl, &pConn->pTimer);
 
   rpcUnlockConn(pConn);
-  return ret;
+
+  if(ret == BOOL_FALSE) {
+    // try next ip again
+    pContext->code = terrno;
+    // in rpcProcessConnError if numOfTry over limit, could call rpcNotifyClient to stop query
+    taosTmrStart(rpcProcessConnError, 1, pContext, pRpc->tmrCtrl);
+    return BOOL_ASYNC;
+  }
+
+  return BOOL_TRUE;
 }
 
 static bool rpcSendMsgToPeer(SRpcConn *pConn, void *msg, int msgLen) {
@@ -1478,8 +1488,6 @@ static void rpcProcessConnError(void *param, void *id) {
     return;
   }
   
-  tDebug("%s %p, connection error happens", pRpc->label, pContext->ahandle);
-
   if (pContext->numOfTry >= pContext->epSet.numOfEps || pContext->msgType == TSDB_MSG_TYPE_FETCH) {
     rpcMsg.msgType = pContext->msgType+1;
     rpcMsg.ahandle = pContext->ahandle;
@@ -1487,9 +1495,11 @@ static void rpcProcessConnError(void *param, void *id) {
     rpcMsg.pCont = NULL;
     rpcMsg.contLen = 0;
 
+    tWarn("%s %p, connection error. notify client query over. numOfTry=%d msgType=%d", pRpc->label, pContext->ahandle, pContext->numOfTry, pContext->msgType);
     rpcNotifyClient(pContext, &rpcMsg);
   } else {
     // move to next IP 
+    tWarn("%s %p, connection error. retry to send request again. numOfTry=%d msgType=%d", pRpc->label, pContext->ahandle, pContext->numOfTry, pContext->msgType);
     pContext->epSet.inUse++;
     pContext->epSet.inUse = pContext->epSet.inUse % pContext->epSet.numOfEps;
     rpcSendReqToServer(pRpc, pContext);
diff --git a/src/util/src/terror.c b/src/util/src/terror.c
index 640e842de340..f66152988ee3 100644
--- a/src/util/src/terror.c
+++ b/src/util/src/terror.c
@@ -125,6 +125,7 @@ TAOS_DEFINE_ERROR(TSDB_CODE_TSC_INVALID_PROTOCOL_TYPE,    "Invalid line protocol
 TAOS_DEFINE_ERROR(TSDB_CODE_TSC_INVALID_PRECISION_TYPE,   "Invalid timestamp precision type")
 TAOS_DEFINE_ERROR(TSDB_CODE_TSC_RES_TOO_MANY,             "Result set too large to be output")
 TAOS_DEFINE_ERROR(TSDB_CODE_TSC_TOO_MANY_SML_LINES,       "Too many lines in batch")
+TAOS_DEFINE_ERROR(TSDB_CODE_TSC_SEND_DATA_FAILED,         "Client send request data failed")
 
 // mnode
 TAOS_DEFINE_ERROR(TSDB_CODE_MND_MSG_NOT_PROCESSED,        "Message not processed")