diff --git a/src/client/src/tscLocalMerge.c b/src/client/src/tscLocalMerge.c
index f64287bdc4f2bfbe326d3a926673761e265c087d..bc3c33423f85fcc9c81e122b9a4e3904f598410a 100644
--- a/src/client/src/tscLocalMerge.c
+++ b/src/client/src/tscLocalMerge.c
@@ -413,13 +413,13 @@ static int32_t tscFlushTmpBufferImpl(tExtMemBuffer *pMemoryBuf, tOrderDescriptor
 }
 
 int32_t tscFlushTmpBuffer(tExtMemBuffer *pMemoryBuf, tOrderDescriptor *pDesc, tFilePage *pPage, int32_t orderType) {
-  int32_t ret = tscFlushTmpBufferImpl(pMemoryBuf, pDesc, pPage, orderType);
-  if (ret != 0) {
-    return -1;
+  int32_t ret = 0;
+  if ((ret = tscFlushTmpBufferImpl(pMemoryBuf, pDesc, pPage, orderType)) != 0) {
+    return ret;
   }
 
-  if (!tExtMemBufferFlush(pMemoryBuf)) {
-    return -1;
+  if ((ret = tExtMemBufferFlush(pMemoryBuf)) != 0) {
+    return ret;
   }
 
   return 0;
@@ -440,9 +440,9 @@ int32_t saveToBuffer(tExtMemBuffer *pMemoryBuf, tOrderDescriptor *pDesc, tFilePa
 
   // current buffer is full, need to flushed to disk
   assert(pPage->num == pModel->capacity);
-  int32_t ret = tscFlushTmpBuffer(pMemoryBuf, pDesc, pPage, orderType);
-  if (ret != 0) {
-    return -1;
+  int32_t code = tscFlushTmpBuffer(pMemoryBuf, pDesc, pPage, orderType);
+  if (code != 0) {
+    return code;
   }
 
   int32_t remain = numOfRows - numOfRemainEntries;
@@ -458,8 +458,8 @@ int32_t saveToBuffer(tExtMemBuffer *pMemoryBuf, tOrderDescriptor *pDesc, tFilePa
     tColModelAppend(pModel, pPage, data, numOfRows - remain, numOfWriteElems, numOfRows);
 
     if (pPage->num == pModel->capacity) {
-      if (tscFlushTmpBuffer(pMemoryBuf, pDesc, pPage, orderType) != TSDB_CODE_SUCCESS) {
-        return -1;
+      if ((code = tscFlushTmpBuffer(pMemoryBuf, pDesc, pPage, orderType)) != TSDB_CODE_SUCCESS) {
+        return code;
       }
     } else {
       pPage->num = numOfWriteElems;
diff --git a/src/client/src/tscSQLParser.c b/src/client/src/tscSQLParser.c
index 788d53e00a0763ed09de4b6b7815adf3d8f735c3..6164c005b94aa4a5a6a20f5dd08f25f382d053a2 100644
--- a/src/client/src/tscSQLParser.c
+++ b/src/client/src/tscSQLParser.c
@@ -2622,7 +2622,7 @@ static int32_t doExtractColumnFilterInfo(SQueryInfo* pQueryInfo, SColumnFilterIn
     tVariantDump(&pRight->val, (char*)&pColumnFilter->upperBndd, colType, false);
   } else {  // TK_GT,TK_GE,TK_EQ,TK_NE are based on the pColumn->lowerBndd
     if (colType == TSDB_DATA_TYPE_BINARY) {
-      pColumnFilter->pz = (int64_t)calloc(1, pRight->val.nLen + 1);
+      pColumnFilter->pz = (int64_t)calloc(1, pRight->val.nLen + TSDB_NCHAR_SIZE);
       pColumnFilter->len = pRight->val.nLen;
 
       tVariantDump(&pRight->val, (char*)pColumnFilter->pz, colType, false);
diff --git a/src/client/src/tscServer.c b/src/client/src/tscServer.c
index e15a5e618ad0dbd3aac1751fa543c50692443f6c..1384dcecff04b197dae5bd8209cd767c2fd0d7cf 100644
--- a/src/client/src/tscServer.c
+++ b/src/client/src/tscServer.c
@@ -198,6 +198,8 @@ int tscSendMsgToServer(SSqlObj *pSql) {
   };
 
   pSql->SRpcReqContext = rpcSendRequest(pObj->pDnodeConn, &pSql->ipList, &rpcMsg);
+  assert(pSql->SRpcReqContext != NULL);
+
   return TSDB_CODE_SUCCESS;
 }
 
@@ -412,7 +414,6 @@ void tscKillSTableQuery(SSqlObj *pSql) {
 
   for (int i = 0; i < pSql->numOfSubs; ++i) {
     SSqlObj *pSub = pSql->pSubs[i];
-
     if (pSub == NULL) {
       continue;
     }
diff --git a/src/client/src/tscSql.c b/src/client/src/tscSql.c
index 0be7db435d679eb3ce8452975c59f754fd2e5cbf..6d4337e03276bdb51b5c93031fc2e2c52246b9b5 100644
--- a/src/client/src/tscSql.c
+++ b/src/client/src/tscSql.c
@@ -607,7 +607,9 @@ int* taos_fetch_lengths(TAOS_RES *res) {
 char *taos_get_client_info() { return version; }
 
 void taos_stop_query(TAOS_RES *res) {
-  if (res == NULL) return;
+  if (res == NULL) {
+    return;
+  }
 
   SSqlObj *pSql = (SSqlObj *)res;
   SSqlCmd *pCmd = &pSql->cmd;
diff --git a/src/client/src/tscSubquery.c b/src/client/src/tscSubquery.c
index 42a5d1d09bc16fba0cda1865cee5cbfbdbf4138c..a3e655a9711fe0df8a8bac95846a0869d2b1a6ca 100644
--- a/src/client/src/tscSubquery.c
+++ b/src/client/src/tscSubquery.c
@@ -1492,7 +1492,7 @@ static void tscAbortFurtherRetryRetrieval(SRetrieveSupport *trsupport, TAOS_RES
   tscError("sub:%p failed to flush data to disk:reason:%s", tres, lpMsgBuf);
   LocalFree(lpMsgBuf);
 #else
-  tscError("sub:%p failed to flush data to disk:reason:%s", tres, strerror(errno));
+  tscError("sub:%p failed to flush data to disk, reason:%s", tres, tstrerror(code));
 #endif
 
   SSqlObj* pParentSql = trsupport->pParentSqlObj;
@@ -1501,7 +1501,6 @@ static void tscAbortFurtherRetryRetrieval(SRetrieveSupport *trsupport, TAOS_RES
   trsupport->numOfRetry = MAX_NUM_OF_SUBQUERY_RETRY;
   
   pthread_mutex_unlock(&trsupport->queryMutex);
-  
   tscHandleSubqueryError(trsupport, tres, pParentSql->res.code);
 }
 
@@ -1630,10 +1629,9 @@ static void tscAllDataRetrievedFromDnode(SRetrieveSupport *trsupport, SSqlObj* p
   
   // each result for a vnode is ordered as an independant list,
   // then used as an input of loser tree for disk-based merge routine
-  int32_t ret = tscFlushTmpBuffer(trsupport->pExtMemBuffer[idx], pDesc, trsupport->localBuffer,
-                                  pQueryInfo->groupbyExpr.orderType);
-  if (ret != 0) { // set no disk space error info, and abort retry
-    return tscAbortFurtherRetryRetrieval(trsupport, pSql, TSDB_CODE_TSC_NO_DISKSPACE);
+  int32_t code = tscFlushTmpBuffer(trsupport->pExtMemBuffer[idx], pDesc, trsupport->localBuffer, pQueryInfo->groupbyExpr.orderType);
+  if (code != 0) { // set no disk space error info, and abort retry
+    return tscAbortFurtherRetryRetrieval(trsupport, pSql, code);
   }
   
   int32_t remain = -1;
@@ -1704,7 +1702,7 @@ static void tscRetrieveFromDnodeCallBack(void *param, TAOS_RES *tres, int numOfR
     
     tscTrace("%p sub:%p retrieve numOfRows:%" PRId64 " totalNumOfRows:%" PRIu64 " from ip:%s, orderOfSub:%d", pPObj, pSql,
              pRes->numOfRows, pState->numOfRetrievedRows, pSql->ipList.fqdn[pSql->ipList.inUse], idx);
-    
+
     if (num > tsMaxNumOfOrderedResults && tscIsProjectionQueryOnSTable(pQueryInfo, 0)) {
       tscError("%p sub:%p num of OrderedRes is too many, max allowed:%" PRId32 " , current:%" PRId64,
                pPObj, pSql, tsMaxNumOfOrderedResults, num);
@@ -1729,7 +1727,7 @@ static void tscRetrieveFromDnodeCallBack(void *param, TAOS_RES *tres, int numOfR
     
     int32_t ret = saveToBuffer(trsupport->pExtMemBuffer[idx], pDesc, trsupport->localBuffer, pRes->data,
                                pRes->numOfRows, pQueryInfo->groupbyExpr.orderType);
-    if (ret < 0) { // set no disk space error info, and abort retry
+    if (ret != 0) { // set no disk space error info, and abort retry
       tscAbortFurtherRetryRetrieval(trsupport, tres, TSDB_CODE_TSC_NO_DISKSPACE);
       pthread_mutex_unlock(&trsupport->queryMutex);
       
@@ -1988,6 +1986,7 @@ void tscBuildResFromSubqueries(SSqlObj *pSql) {
         SColumnIndex* pIndex = &pRes->pColumnIndex[i];
         SSqlRes *pRes1 = &pSql->pSubs[pIndex->tableIndex]->res;
         pRes->tsrow[i] = pRes1->tsrow[pIndex->columnIndex];
+        pRes->length[i] = pRes1->length[pIndex->columnIndex];
       }
       
       pRes->numOfClauseTotal++;
diff --git a/src/kit/shell/src/shellEngine.c b/src/kit/shell/src/shellEngine.c
index f2ba5201ba0c3b4d454dc9de047ccd0ceb4a6884..e28c691a8986fce0bcb7a04b8bb1e5f7f5c6605c 100644
--- a/src/kit/shell/src/shellEngine.c
+++ b/src/kit/shell/src/shellEngine.c
@@ -276,6 +276,8 @@ void shellRunCommandOnServer(TAOS *con, char command[]) {
   st = taosGetTimestampUs();
 
   TAOS_RES* pSql = taos_query(con, command);
+  result = pSql;  // set it into the global variable
+
   if (taos_errno(pSql)) {
     taos_error(pSql);
     return;
@@ -284,7 +286,8 @@ void shellRunCommandOnServer(TAOS *con, char command[]) {
   if (regex_match(command, "^\\s*use\\s+[a-zA-Z0-9_]+\\s*;\\s*$", REG_EXTENDED | REG_ICASE)) {
     fprintf(stdout, "Database changed.\n\n");
     fflush(stdout);
-    
+
+    result = NULL;
     taos_free_result(pSql);
     return;
   }
@@ -294,6 +297,7 @@ void shellRunCommandOnServer(TAOS *con, char command[]) {
     int error_no = 0;
     int numOfRows = shellDumpResult(pSql, fname, &error_no, printMode);
     if (numOfRows < 0) {
+      result = NULL;
       taos_free_result(pSql);
       return;
     }
@@ -315,7 +319,8 @@ void shellRunCommandOnServer(TAOS *con, char command[]) {
   if (fname != NULL) {
     wordfree(&full_path);
   }
-  
+
+  result = NULL;
   taos_free_result(pSql);
 }
 
@@ -419,8 +424,8 @@ static void dumpFieldToFile(FILE* fp, const char* val, TAOS_FIELD* field, int32_
   }
 }
 
-static int dumpResultToFile(const char* fname, TAOS_RES* result) {
-  TAOS_ROW row = taos_fetch_row(result);
+static int dumpResultToFile(const char* fname, TAOS_RES* tres) {
+  TAOS_ROW row = taos_fetch_row(tres);
   if (row == NULL) {
     return 0;
   }
@@ -441,9 +446,9 @@ static int dumpResultToFile(const char* fname, TAOS_RES* result) {
 
   wordfree(&full_path);
 
-  int num_fields = taos_num_fields(result);
-  TAOS_FIELD *fields = taos_fetch_fields(result);
-  int precision = taos_result_precision(result);
+  int num_fields = taos_num_fields(tres);
+  TAOS_FIELD *fields = taos_fetch_fields(tres);
+  int precision = taos_result_precision(tres);
 
   for (int col = 0; col < num_fields; col++) {
     if (col > 0) {
@@ -455,7 +460,7 @@ static int dumpResultToFile(const char* fname, TAOS_RES* result) {
   
   int numOfRows = 0;
   do {
-    int32_t* length = taos_fetch_lengths(result);
+    int32_t* length = taos_fetch_lengths(tres);
     for (int i = 0; i < num_fields; i++) {
       if (i > 0) {
         fputc(',', fp);
@@ -465,10 +470,13 @@ static int dumpResultToFile(const char* fname, TAOS_RES* result) {
     fputc('\n', fp);
 
     numOfRows++;
-    row = taos_fetch_row(result);
+    row = taos_fetch_row(tres);
   } while( row != NULL);
 
+  result = NULL;
+  taos_free_result(tres);
   fclose(fp);
+
   return numOfRows;
 }
 
@@ -769,8 +777,7 @@ void write_history() {
 
 void taos_error(TAOS_RES *tres) {
   fprintf(stderr, "\nDB error: %s\n", taos_errstr(tres));
-
-  /* free local resouce: allocated memory/metric-meta refcnt */
+  result = NULL;
   taos_free_result(tres);
 }
 
@@ -845,9 +852,9 @@ void shellGetGrantInfo(void *con) {
 
   char sql[] = "show grants";
 
-  result = taos_query(con, sql);
+  TAOS_RES* tres = taos_query(con, sql);
 
-  int code = taos_errno(result);
+  int code = taos_errno(tres);
   if (code != TSDB_CODE_SUCCESS) {
     if (code == TSDB_CODE_COM_OPS_NOT_SUPPORT) {
       fprintf(stdout, "Server is Community Edition, version is %s\n\n", taos_get_server_info(con));
@@ -857,18 +864,18 @@ void shellGetGrantInfo(void *con) {
     return;
   }
 
-  int num_fields = taos_field_count(result);
+  int num_fields = taos_field_count(tres);
   if (num_fields == 0) {
     fprintf(stderr, "\nInvalid grant information.\n");
     exit(0);
   } else {
-    if (result == NULL) {
+    if (tres == NULL) {
       fprintf(stderr, "\nGrant information is null.\n");
       exit(0);
     }
 
-    TAOS_FIELD *fields = taos_fetch_fields(result);
-    TAOS_ROW row = taos_fetch_row(result);
+    TAOS_FIELD *fields = taos_fetch_fields(tres);
+    TAOS_ROW row = taos_fetch_row(tres);
     if (row == NULL) {
       fprintf(stderr, "\nFailed to get grant information from server. Abort.\n");
       exit(0);
@@ -888,8 +895,8 @@ void shellGetGrantInfo(void *con) {
       fprintf(stdout, "Server is Enterprise %s Edition, version is %s and will expire at %s.\n", serverVersion, taos_get_server_info(con), expiretime);
     }
 
-    taos_free_result(result);
     result = NULL;
+    taos_free_result(tres);
   }
 
   fprintf(stdout, "\n");
diff --git a/src/kit/shell/src/shellMain.c b/src/kit/shell/src/shellMain.c
index 92474bdd03f56e6b5b0e0bde17a94a10606ac8d4..8481f498dd395cd449192d625d307ae812acaa30 100644
--- a/src/kit/shell/src/shellMain.c
+++ b/src/kit/shell/src/shellMain.c
@@ -15,7 +15,6 @@
 
 #include "os.h"
 #include "shell.h"
-#include "tsclient.h"
 
 pthread_t pid;
 
@@ -23,14 +22,6 @@ pthread_t pid;
 void interruptHandler(int signum) {
 #ifdef LINUX
   taos_stop_query(result);
-  if (result != NULL) {
-    /*
-     * we need to free result in async model, in order to avoid free
-     * results while the master thread is waiting for server response.
-     */
-    tscQueueAsyncFreeResult(result);
-  }
-  
   result = NULL;
 #else
   printf("\nReceive ctrl+c or other signal, quit shell.\n");
diff --git a/src/kit/taosdump/taosdump.c b/src/kit/taosdump/taosdump.c
index 0b881864f2253de5caeebbe501c9be440d5b262d..7fa7ffa3a949176703b850c16b70e45c01454cdd 100644
--- a/src/kit/taosdump/taosdump.c
+++ b/src/kit/taosdump/taosdump.c
@@ -295,7 +295,6 @@ static error_t parse_opt(int key, char *arg, struct argp_state *state) {
 static struct argp argp = {options, parse_opt, args_doc, doc};
 
 TAOS *taos = NULL;
-TAOS_RES *result = NULL;
 char *command = NULL;
 char *lcommand = NULL;
 char *buffer = NULL;
@@ -465,10 +464,10 @@ int taosDumpOut(SDumpArguments *arguments) {
   taosDumpCharset(fp);
 
   sprintf(command, "show databases");
-  result = taos_query(taos, command);
+  TAOS_RES* result = taos_query(taos, command);
   int32_t code = taos_errno(result);
   if (code != 0) {
-    fprintf(stderr, "failed to run command: %s, reason: %s\n", command, taos_errstr(taos));
+    fprintf(stderr, "failed to run command: %s, reason: %s\n", command, taos_errstr(result));
     taos_free_result(result);
     goto _exit_failure;
   }
@@ -615,7 +614,7 @@ int taosDumpDb(SDbInfo *dbInfo, SDumpArguments *arguments, FILE *fp) {
   fprintf(fp, "USE %s\n\n", dbInfo->name);
 
   sprintf(command, "show tables");
-  result = taos_query(taos,command);
+  TAOS_RES* result = taos_query(taos,command);
   int32_t code = taos_errno(result);
   if (code != 0) {
     fprintf(stderr, "failed to run command %s, error: %s\n", command, taos_errstr(result));
@@ -719,7 +718,7 @@ void taosDumpCreateMTableClause(STableDef *tableDes, char *metric, int numOfCols
 
     sprintf(command, "select %s from %s limit 1", tableDes->cols[counter].field, tableDes->name);
 
-    result = taos_query(taos, command);
+    TAOS_RES* result = taos_query(taos, command);
     int32_t code = taos_errno(result);
     if (code != 0) {
       fprintf(stderr, "failed to run command %s, error: %s\n", command, taos_errstr(result));
@@ -797,7 +796,7 @@ int taosGetTableDes(char *table, STableDef *tableDes) {
 
   sprintf(command, "describe %s", table);
 
-  result = taos_query(taos, command);
+  TAOS_RES* result = taos_query(taos, command);
   int32_t code = taos_errno(result);
   if (code != 0) {
     fprintf(stderr, "failed to run command %s, error: %s\n", command, taos_errstr(result));
@@ -877,7 +876,7 @@ int32_t taosDumpMetric(char *metric, SDumpArguments *arguments, FILE *fp) {
   tstrncpy(tableRecord.metric, metric, TSDB_TABLE_NAME_LEN);
 
   sprintf(command, "select tbname from %s", metric);
-  result = taos_query(taos, command);
+  TAOS_RES* result = taos_query(taos, command);
   int32_t code = taos_errno(result);
   if (code != 0) {
     fprintf(stderr, "failed to run command %s, error: %s\n", command, taos_errstr(result));
@@ -930,7 +929,7 @@ int taosDumpTableData(FILE *fp, char *tbname, SDumpArguments *arguments) {
   sprintf(command, "select * from %s where _c0 >= %" PRId64 " and _c0 <= %" PRId64 " order by _c0 asc", tbname, arguments->start_time,
           arguments->end_time);
           
-  result = taos_query(taos, command);
+  TAOS_RES* result = taos_query(taos, command);
   int32_t code = taos_errno(result);
   if (code != 0) {
     fprintf(stderr, "failed to run command %s, reason: %s\n", command, taos_errstr(result));
@@ -1179,9 +1178,13 @@ int taosDumpIn(SDumpArguments *arguments) {
           tcommand = command;
         }
         taosReplaceCtrlChar(tcommand);
-        if (taos_query(taos, tcommand) == NULL)
+
+        TAOS_RES* result = taos_query(taos, tcommand);
+        if (taos_errno(result) != 0){
           fprintf(stderr, "linenu: %" PRId64 " failed to run command %s reason:%s \ncontinue...\n", linenu, command,
-                  taos_errstr(taos));
+                  taos_errstr(result));
+          taos_free_result(result);
+        }
 
         pstr = command;
         pstr[0] = '\0';
@@ -1227,12 +1230,12 @@ int taosDumpIn(SDumpArguments *arguments) {
         tcommand = command;
       }
       taosReplaceCtrlChar(tcommand);
-      result = taos_query(taos, tcommand);
+      TAOS_RES* result = taos_query(taos, tcommand);
       int32_t code = taos_errno(result);
       if (code != 0) 
       {
         fprintf(stderr, "linenu:%" PRId64 " failed to run command %s reason: %s \ncontinue...\n", linenu, command,
-                taos_errstr(taos));
+                taos_errstr(result));
       }
       taos_free_result(result);
     }
diff --git a/src/query/inc/qextbuffer.h b/src/query/inc/qextbuffer.h
index 23b67083e593f5eab88b11f1f960d6af7138f3e9..2cbef2b1bea66654b262a3fb37061477969960f2 100644
--- a/src/query/inc/qextbuffer.h
+++ b/src/query/inc/qextbuffer.h
@@ -149,7 +149,7 @@ int16_t tExtMemBufferPut(tExtMemBuffer *pMemBuffer, void *data, int32_t numOfRow
  * @param pMemBuffer
  * @return
  */
-bool tExtMemBufferFlush(tExtMemBuffer *pMemBuffer);
+int32_t tExtMemBufferFlush(tExtMemBuffer *pMemBuffer);
 
 /**
  *
diff --git a/src/query/src/qextbuffer.c b/src/query/src/qextbuffer.c
index e0a90e04082706eb720960e88356df466dbd017f..35f5e22ed51b9261fa621520d5757a777e9973c8 100644
--- a/src/query/src/qextbuffer.c
+++ b/src/query/src/qextbuffer.c
@@ -245,30 +245,29 @@ static void tExtMemBufferClearFlushoutInfo(tExtMemBuffer *pMemBuffer) {
   memset(pFileMeta->flushoutData.pFlushoutInfo, 0, sizeof(tFlushoutInfo) * pFileMeta->flushoutData.nAllocSize);
 }
 
-bool tExtMemBufferFlush(tExtMemBuffer *pMemBuffer) {
+int32_t tExtMemBufferFlush(tExtMemBuffer *pMemBuffer) {
+  int32_t ret = 0;
   if (pMemBuffer->numOfTotalElems == 0) {
-    return true;
+    return ret;
   }
 
   if (pMemBuffer->file == NULL) {
     if ((pMemBuffer->file = fopen(pMemBuffer->path, "wb+")) == NULL) {
-      return false;
+      ret = TAOS_SYSTEM_ERROR(errno);
+      return ret;
     }
   }
 
   /* all data has been flushed to disk, ignore flush operation */
   if (pMemBuffer->numOfElemsInBuffer == 0) {
-    return true;
+    return ret;
   }
 
-  bool ret = true;
-  
   tFilePagesItem *first = pMemBuffer->pHead;
-
   while (first != NULL) {
     size_t retVal = fwrite((char *)&(first->item), pMemBuffer->pageSize, 1, pMemBuffer->file);
     if (retVal <= 0) {  // failed to write to buffer, may be not enough space
-      ret = false;
+      ret = TAOS_SYSTEM_ERROR(errno);
     }
 
     pMemBuffer->fileMeta.numOfElemsInFile += first->item.num;