diff --git a/include/common/tglobal.h b/include/common/tglobal.h
index 57d1199e17cd701696054b7d962de3bef9bba8c8..9111728e1ad15d7cfc105a5a65ee8364f7ab2f95 100644
--- a/include/common/tglobal.h
+++ b/include/common/tglobal.h
@@ -146,6 +146,7 @@ struct SConfig *taosGetCfg();
 void    taosSetAllDebugFlag(int32_t flag);
 void    taosSetDebugFlag(int32_t *pFlagPtr, const char *flagName, int32_t flagVal);
 int32_t taosSetCfg(SConfig *pCfg, char *name);
+void    taosLocalCfgForbiddenToChange(char* name, bool* forbidden);
 
 #ifdef __cplusplus
 }
diff --git a/include/os/osString.h b/include/os/osString.h
index 3a4ff18694489c995c8849bcd9c39a14637472c2..8eb341faa7bf61e4c2f67f8a21859da94c0dcbf4 100644
--- a/include/os/osString.h
+++ b/include/os/osString.h
@@ -62,6 +62,8 @@ typedef int32_t TdUcs4;
 int32_t taosUcs4len(TdUcs4 *ucs4);
 int64_t taosStr2int64(const char *str);
 
+void    taosConvInit(void);
+void    taosConvDestroy();
 int32_t taosUcs4ToMbs(TdUcs4 *ucs4, int32_t ucs4_max_len, char *mbs);
 bool    taosMbsToUcs4(const char *mbs, size_t mbs_len, TdUcs4 *ucs4, int32_t ucs4_max_len, int32_t *len);
 int32_t tasoUcs4Compare(TdUcs4 *f1_ucs4, TdUcs4 *f2_ucs4, int32_t bytes);
diff --git a/source/client/src/clientEnv.c b/source/client/src/clientEnv.c
index 893aa39ce3a74db33f6520bab7455a2331c74a0e..3d539ea25135022cb556837c81f96e090a3cac22 100644
--- a/source/client/src/clientEnv.c
+++ b/source/client/src/clientEnv.c
@@ -361,6 +361,8 @@ void taos_init_imp(void) {
 
   initQueryModuleMsgHandle();
 
+  taosConvInit();
+  
   rpcInit();
 
   SCatalogCfg cfg = {.maxDBCacheNum = 100, .maxTblCacheNum = 100};
diff --git a/source/client/src/clientHb.c b/source/client/src/clientHb.c
index 3d6cf1c626c3bbbe695ea35ba6316439b7886eb3..06bd3f388741edd21e69dc5f1128937f1739feea 100644
--- a/source/client/src/clientHb.c
+++ b/source/client/src/clientHb.c
@@ -353,6 +353,7 @@ int32_t hbBuildQueryDesc(SQueryHbReqBasic *hbBasic, STscObj *pObj) {
         desc.subDesc = NULL;
         desc.subPlanNum = 0;
       }
+      desc.subPlanNum = taosArrayGetSize(desc.subDesc);
       ASSERT(desc.subPlanNum == taosArrayGetSize(desc.subDesc));
     } else {
       desc.subDesc = NULL;
diff --git a/source/client/src/clientMain.c b/source/client/src/clientMain.c
index b04b4ea2aa771c63883d6668f3f7d5a9f8778add..a4eaf057d12ba3e2a57190de0f76a9489ae8fc61 100644
--- a/source/client/src/clientMain.c
+++ b/source/client/src/clientMain.c
@@ -75,6 +75,8 @@ void taos_cleanup(void) {
 
   cleanupTaskQueue();
 
+  taosConvDestroy();
+  
   tscInfo("all local resources released");
   taosCleanupCfg();
   taosCloseLog();
diff --git a/source/common/src/tglobal.c b/source/common/src/tglobal.c
index 0cc4e31aed97f235b38ed26f850c1e7e13276bd0..6f4a3060ed99baf08ee465bfd0c9c4f6baede9fa 100644
--- a/source/common/src/tglobal.c
+++ b/source/common/src/tglobal.c
@@ -49,7 +49,7 @@ int32_t tsNumOfShmThreads = 1;
 // queue & threads
 int32_t tsNumOfRpcThreads = 1;
 int32_t tsNumOfCommitThreads = 2;
-int32_t tsNumOfTaskQueueThreads = 1;
+int32_t tsNumOfTaskQueueThreads = 4;
 int32_t tsNumOfMnodeQueryThreads = 4;
 int32_t tsNumOfMnodeFetchThreads = 1;
 int32_t tsNumOfMnodeReadThreads = 1;
@@ -317,9 +317,9 @@ static int32_t taosAddClientCfg(SConfig *pCfg) {
   if (cfgAddString(pCfg, "smlTagName", tsSmlTagName, 1) != 0) return -1;
   if (cfgAddBool(pCfg, "smlDataFormat", tsSmlDataFormat, 1) != 0) return -1;
 
-  tsNumOfTaskQueueThreads = tsNumOfCores / 4;
-  tsNumOfTaskQueueThreads = TRANGE(tsNumOfTaskQueueThreads, 1, 2);
-  if (cfgAddInt32(pCfg, "numOfTaskQueueThreads", tsNumOfTaskQueueThreads, 1, 1024, 0) != 0) return -1;
+  tsNumOfTaskQueueThreads = tsNumOfCores / 2;
+  tsNumOfTaskQueueThreads = TMAX(tsNumOfTaskQueueThreads, 4);
+  if (cfgAddInt32(pCfg, "numOfTaskQueueThreads", tsNumOfTaskQueueThreads, 4, 1024, 0) != 0) return -1;
 
   return 0;
 }
@@ -594,6 +594,20 @@ static int32_t taosSetServerCfg(SConfig *pCfg) {
   return 0;
 }
 
+void taosLocalCfgForbiddenToChange(char* name, bool* forbidden) {
+  int32_t len = strlen(name);
+  char    lowcaseName[CFG_NAME_MAX_LEN + 1] = {0};
+  strntolower(lowcaseName, name, TMIN(CFG_NAME_MAX_LEN, len));
+
+  if (strcasecmp("charset", name) == 0) {
+    *forbidden = true;
+    return;
+  }
+
+  *forbidden = false;
+}
+
+
 int32_t taosSetCfg(SConfig *pCfg, char *name) {
   int32_t len = strlen(name);
   char    lowcaseName[CFG_NAME_MAX_LEN + 1] = {0};
diff --git a/source/dnode/mgmt/exe/dmMain.c b/source/dnode/mgmt/exe/dmMain.c
index 34c3b40556361297f8d368bf47e5ed8800bd8547..4030eaa6fe2fd32ec5718b6e4f7689f619747366 100644
--- a/source/dnode/mgmt/exe/dmMain.c
+++ b/source/dnode/mgmt/exe/dmMain.c
@@ -218,6 +218,8 @@ int mainWindows(int argc,char** argv) {
     taosCleanupArgs();
     return -1;
   }
+  
+  taosConvInit();
 
   if (global.dumpConfig) {
     dmDumpCfg();
diff --git a/source/dnode/mgmt/node_mgmt/src/dmMgmt.c b/source/dnode/mgmt/node_mgmt/src/dmMgmt.c
index c2e8a552717041798dea4f7ac61045eb198c170d..582b16ce997bc5f87d4842904cda88861e6f8137 100644
--- a/source/dnode/mgmt/node_mgmt/src/dmMgmt.c
+++ b/source/dnode/mgmt/node_mgmt/src/dmMgmt.c
@@ -215,6 +215,7 @@ void dmCleanupDnode(SDnode *pDnode) {
   dmClearVars(pDnode);
   rpcCleanup();
   indexCleanup();
+  taosConvDestroy();
   dDebug("dnode is closed, ptr:%p", pDnode);
 }
 
diff --git a/source/libs/command/src/command.c b/source/libs/command/src/command.c
index 7c95e71823ca227420adfcc9054cf15cf838a89e..a76b4574229c06b24d0da641dbe7bca67e2dbe2e 100644
--- a/source/libs/command/src/command.c
+++ b/source/libs/command/src/command.c
@@ -517,6 +517,13 @@ static int32_t execAlterLocal(SAlterLocalStmt* pStmt) {
     goto _return;
   }
 
+  bool forbidden = false;
+  taosLocalCfgForbiddenToChange(pStmt->config, &forbidden);
+  if (forbidden) {
+    terrno = TSDB_CODE_OPS_NOT_SUPPORT;
+    return terrno;
+  }
+
   if (cfgSetItem(tsCfg, pStmt->config, pStmt->value, CFG_STYPE_ALTER_CMD)) {
     return terrno;
   }
diff --git a/source/libs/scheduler/src/schJob.c b/source/libs/scheduler/src/schJob.c
index 46140ccdff58eaa79863a4685112dfc64f853ff4..82146c374185d7569c7fe6ac2344e95e302e1391 100644
--- a/source/libs/scheduler/src/schJob.c
+++ b/source/libs/scheduler/src/schJob.c
@@ -278,7 +278,7 @@ int32_t schValidateAndBuildJob(SQueryPlan *pDag, SSchJob *pJob) {
   }
 
   SHashObj *planToTask = taosHashInit(
-      SCHEDULE_DEFAULT_MAX_TASK_NUM,
+      pDag->numOfSubplans,
       taosGetDefaultHashFunction(POINTER_BYTES == sizeof(int64_t) ? TSDB_DATA_TYPE_BIGINT : TSDB_DATA_TYPE_INT), false,
       HASH_NO_LOCK);
   if (NULL == planToTask) {
diff --git a/source/os/src/osString.c b/source/os/src/osString.c
index 32f0fdf7b3ace44d51f4b4203e6b494f342a7ccb..26aafd743fb7ad8a89e0f73674d25eb98a884147 100644
--- a/source/os/src/osString.c
+++ b/source/os/src/osString.c
@@ -134,21 +134,95 @@ int32_t taosUcs4ToMbs(TdUcs4 *ucs4, int32_t ucs4_max_len, char *mbs) {
 #endif
 }
 
+typedef struct {
+  iconv_t conv;
+  int8_t  inUse;
+} SConv;
+
+SConv *gConv = NULL;
+int32_t convUsed = 0;
+int32_t gConvMaxNum = 0;
+
+void taosConvInit(void) {
+  gConvMaxNum = 512;
+  gConv = taosMemoryCalloc(gConvMaxNum, sizeof(SConv));
+  for (int32_t i = 0; i < gConvMaxNum; ++i) {
+    gConv[i].conv = iconv_open(DEFAULT_UNICODE_ENCODEC, tsCharset);
+    if ((iconv_t)-1 == gConv[i].conv || (iconv_t)0 == gConv[i].conv) {
+      ASSERT(0);
+    }
+  }
+}
+
+void taosConvDestroy() {
+  for (int32_t i = 0; i < gConvMaxNum; ++i) {
+    iconv_close(gConv[i].conv);
+  }
+  taosMemoryFreeClear(gConv);
+  gConvMaxNum = -1;
+}
+
+iconv_t taosAcquireConv(int32_t *idx) {
+  if (gConvMaxNum <= 0) {
+    *idx = -1;
+    return iconv_open(DEFAULT_UNICODE_ENCODEC, tsCharset);
+  }
+  
+  while (true) {
+    int32_t used = atomic_add_fetch_32(&convUsed, 1);
+    if (used > gConvMaxNum) {
+      used = atomic_sub_fetch_32(&convUsed, 1);
+      sched_yield();
+      continue;
+    }
+    
+    break;
+  }
+
+  int32_t startId = taosGetSelfPthreadId() % gConvMaxNum;
+  while (true) {
+    if (gConv[startId].inUse) {
+      startId = (startId + 1) % gConvMaxNum;
+      continue;
+    }
+
+    int8_t old = atomic_val_compare_exchange_8(&gConv[startId].inUse, 0, 1);
+    if (0 == old) {
+      break;
+    }
+  }
+
+  *idx = startId;
+  return gConv[startId].conv;
+}
+
+void taosReleaseConv(int32_t idx, iconv_t conv) {
+  if (idx < 0) {
+    iconv_close(conv);
+    return;
+  }
+
+  atomic_store_8(&gConv[idx].inUse, 0);
+  atomic_sub_fetch_32(&convUsed, 1);
+}
+
 bool taosMbsToUcs4(const char *mbs, size_t mbsLength, TdUcs4 *ucs4, int32_t ucs4_max_len, int32_t *len) {
 #ifdef DISALLOW_NCHAR_WITHOUT_ICONV
   printf("Nchar cannot be read and written without iconv, please install iconv library and recompile TDengine.\n");
   return -1;
 #else
   memset(ucs4, 0, ucs4_max_len);
-  iconv_t cd = iconv_open(DEFAULT_UNICODE_ENCODEC, tsCharset);
+
+  int32_t idx = -1;
+  iconv_t conv = taosAcquireConv(&idx);
   size_t  ucs4_input_len = mbsLength;
   size_t  outLeft = ucs4_max_len;
-  if (iconv(cd, (char **)&mbs, &ucs4_input_len, (char **)&ucs4, &outLeft) == -1) {
-    iconv_close(cd);
+  if (iconv(conv, (char **)&mbs, &ucs4_input_len, (char **)&ucs4, &outLeft) == -1) {
+    taosReleaseConv(idx, conv);
     return false;
   }
 
-  iconv_close(cd);
+  taosReleaseConv(idx, conv);
   if (len != NULL) {
     *len = (int32_t)(ucs4_max_len - outLeft);
     if (*len < 0) {