diff --git a/include/common/taosmsg.h b/include/common/taosmsg.h
index 9bae38e3a72dddb276679efb38eb7f38e7e1c455..826934c4a87e8832151567a4e2407c66de5c4d4a 100644
--- a/include/common/taosmsg.h
+++ b/include/common/taosmsg.h
@@ -153,7 +153,8 @@ TAOS_DEFINE_MESSAGE_TYPE( TSDB_MSG_TYPE_DUMMY9, "dummy9" )
 #define TSDB_IE_TYPE_DNODE_EXT 6
 #define TSDB_IE_TYPE_DNODE_STATE 7
 
-enum _mgmt_table {
+typedef enum _mgmt_table {
+  TSDB_MGMT_TABLE_START,
   TSDB_MGMT_TABLE_ACCT,
   TSDB_MGMT_TABLE_USER,
   TSDB_MGMT_TABLE_DB,
@@ -175,7 +176,7 @@ enum _mgmt_table {
   TSDB_MGMT_TABLE_TP,
   TSDB_MGMT_TABLE_FUNCTION,
   TSDB_MGMT_TABLE_MAX,
-};
+} EShowType;
 
 #define TSDB_ALTER_TABLE_ADD_TAG_COLUMN    1
 #define TSDB_ALTER_TABLE_DROP_TAG_COLUMN   2
diff --git a/source/dnode/mgmt/impl/src/dndTransport.c b/source/dnode/mgmt/impl/src/dndTransport.c
index 44ca1d1407f5f5533f07b7d65374043c70d5b389..f3e71564b23b477cb7a344a05c7da46dfffa3bd5 100644
--- a/source/dnode/mgmt/impl/src/dndTransport.c
+++ b/source/dnode/mgmt/impl/src/dndTransport.c
@@ -157,7 +157,7 @@ static int32_t dndInitClient(SDnode *pDnode) {
   rpcInit.label = "DND-C";
   rpcInit.numOfThreads = 1;
   rpcInit.cfp = dndProcessResponse;
-  rpcInit.sessions = 8;
+  rpcInit.sessions = 1024;
   rpcInit.connType = TAOS_CONN_CLIENT;
   rpcInit.idleTime = pDnode->opt.shellActivityTimer * 1000;
   rpcInit.user = INTERNAL_USER;
diff --git a/source/dnode/mnode/impl/inc/mndDef.h b/source/dnode/mnode/impl/inc/mndDef.h
index 9facb8829cebfc98a2a836ae9294b483939d96f4..dc27656dbfd78ad84b956a594c2a95c7e5fbb371 100644
--- a/source/dnode/mnode/impl/inc/mndDef.h
+++ b/source/dnode/mnode/impl/inc/mndDef.h
@@ -281,22 +281,24 @@ typedef struct SFuncObj {
   int16_t type;
 } SFuncObj;
 
-typedef struct {
-  int8_t   type;
-  int8_t   maxReplica;
-  int16_t  numOfColumns;
-  int32_t  index;
-  int32_t  rowSize;
-  int32_t  numOfRows;
-  int32_t  numOfReads;
-  uint16_t payloadLen;
-  void    *pIter;
-  void    *pVgIter;
-  void   **ppShow;
-  char     db[TSDB_FULL_DB_NAME_LEN];
-  int16_t  offset[TSDB_MAX_COLUMNS];
-  int32_t  bytes[TSDB_MAX_COLUMNS];
-  char     payload[];
+typedef struct SShowObj SShowObj;
+typedef struct SShowObj {
+  int8_t     type;
+  int8_t     maxReplica;
+  int16_t    numOfColumns;
+  int32_t    id;
+  int32_t    rowSize;
+  int32_t    numOfRows;
+  int32_t    numOfReads;
+  uint16_t   payloadLen;
+  void      *pIter;
+  void      *pVgIter;
+  SMnode    *pMnode;
+  SShowObj **ppShow;
+  char       db[TSDB_FULL_DB_NAME_LEN];
+  int16_t    offset[TSDB_MAX_COLUMNS];
+  int32_t    bytes[TSDB_MAX_COLUMNS];
+  char       payload[];
 } SShowObj;
 
 typedef struct SMnodeMsg {
diff --git a/source/dnode/mnode/impl/inc/mndInt.h b/source/dnode/mnode/impl/inc/mndInt.h
index 8910ed4e631ef0b46a1d30c61b84ab41f47b61bb..e5643847a5bdd42ce784b92ebb7a95d7e68bf75b 100644
--- a/source/dnode/mnode/impl/inc/mndInt.h
+++ b/source/dnode/mnode/impl/inc/mndInt.h
@@ -18,6 +18,7 @@
 
 #include "mndDef.h"
 #include "sdb.h"
+#include "tcache.h"
 #include "tqueue.h"
 
 #ifdef __cplusplus
@@ -27,6 +28,9 @@ extern "C" {
 typedef int32_t (*MndMsgFp)(SMnode *pMnode, SMnodeMsg *pMsg);
 typedef int32_t (*MndInitFp)(SMnode *pMnode);
 typedef void (*MndCleanupFp)(SMnode *pMnode);
+typedef int32_t (*ShowMetaFp)(SMnode *pMnode, STableMetaMsg *pMeta, SShowObj *pShow, void *pConn);
+typedef int32_t (*ShowRetrieveFp)(SMnode *pMnode, SShowObj *pShow, char *data, int32_t rows, void *pConn);
+typedef void (*ShowFreeIterFp)(SMnode *pMnode, void *pIter);
 
 typedef struct {
   const char  *name;
@@ -34,6 +38,14 @@ typedef struct {
   MndCleanupFp cleanupFp;
 } SMnodeStep;
 
+typedef struct {
+  int32_t        showId;
+  ShowMetaFp     metaFps[TSDB_MGMT_TABLE_MAX];
+  ShowRetrieveFp retrieveFps[TSDB_MGMT_TABLE_MAX];
+  ShowFreeIterFp freeIterFps[TSDB_MGMT_TABLE_MAX];
+  SCacheObj     *cache;
+} SShowMgmt;
+
 typedef struct SMnode {
   int32_t           dnodeId;
   int32_t           clusterId;
@@ -45,6 +57,7 @@ typedef struct SMnode {
   SSdb             *pSdb;
   SDnode           *pDnode;
   SArray           *pSteps;
+  SShowMgmt         showMgmt;
   MndMsgFp          msgFp[TSDB_MSG_TYPE_MAX];
   SendMsgToDnodeFp  sendMsgToDnodeFp;
   SendMsgToMnodeFp  sendMsgToMnodeFp;
@@ -53,6 +66,7 @@ typedef struct SMnode {
   int32_t           sver;
   int32_t           statusInterval;
   int32_t           mnodeEqualVnodeNum;
+  int32_t           shellActivityTimer;
   char             *timezone;
   char             *locale;
   char             *charset;
diff --git a/source/dnode/mnode/impl/inc/mndShow.h b/source/dnode/mnode/impl/inc/mndShow.h
index 06c18cb0297bf4cfdf2eb604049234b667146a6f..31c0b69c85bcba9f4821f1d0758bbfc20067fbce 100644
--- a/source/dnode/mnode/impl/inc/mndShow.h
+++ b/source/dnode/mnode/impl/inc/mndShow.h
@@ -24,6 +24,10 @@ extern "C" {
 
 int32_t mndInitShow(SMnode *pMnode);
 void    mndCleanupShow(SMnode *pMnode);
+void    mnodeAddShowMetaHandle(SMnode *pMnode, EShowType showType, ShowMetaFp fp);
+void    mnodeAddShowRetrieveHandle(SMnode *pMnode, EShowType showType, ShowRetrieveFp fp);
+void    mnodeAddShowFreeIterHandle(SMnode *pMnode, EShowType msgType, ShowFreeIterFp fp);
+void    mnodeVacuumResult(char *data, int32_t numOfCols, int32_t rows, int32_t capacity, SShowObj *pShow);
 
 #ifdef __cplusplus
 }
diff --git a/source/dnode/mnode/impl/src/mndCluster.c b/source/dnode/mnode/impl/src/mndCluster.c
index 1780c88d6b2ff1e35419212e7f5fc596382bc42d..dbe5dd4f897b2d53999eb5ebcf17316c3efedcec 100644
--- a/source/dnode/mnode/impl/src/mndCluster.c
+++ b/source/dnode/mnode/impl/src/mndCluster.c
@@ -16,6 +16,7 @@
 #define _DEFAULT_SOURCE
 #include "mndCluster.h"
 #include "mndTrans.h"
+#include "mndShow.h"
 
 #define SDB_CLUSTER_VER 1
 
@@ -94,6 +95,71 @@ static int32_t mndCreateDefaultCluster(SMnode *pMnode) {
   return sdbWrite(pMnode->pSdb, pRaw);
 }
 
+
+// static int32_t mnodeGetClusterMeta(STableMetaMsg *pMeta, SShowObj *pShow, void *pConn) {
+//   int32_t cols = 0;
+//   SSchema *pSchema = pMeta->schema;
+
+//   pShow->bytes[cols] = TSDB_CLUSTER_ID_LEN + VARSTR_HEADER_SIZE;
+//   pSchema[cols].type = TSDB_DATA_TYPE_BINARY;
+//   strcpy(pSchema[cols].name, "clusterId");
+//   pSchema[cols].bytes = htons(pShow->bytes[cols]);
+//   cols++;
+
+//   pShow->bytes[cols] = 8;
+//   pSchema[cols].type = TSDB_DATA_TYPE_TIMESTAMP;
+//   strcpy(pSchema[cols].name, "create_time");
+//   pSchema[cols].bytes = htons(pShow->bytes[cols]);
+//   cols++;
+
+//   pMeta->numOfColumns = htons(cols);
+//   strcpy(pMeta->tableFname, "show cluster");
+//   pShow->numOfColumns = cols;
+
+//   pShow->offset[0] = 0;
+//   for (int32_t i = 1; i < cols; ++i) {
+//     pShow->offset[i] = pShow->offset[i - 1] + pShow->bytes[i - 1];
+//   }
+
+//   pShow->numOfRows = 1;
+//   pShow->rowSize = pShow->offset[cols - 1] + pShow->bytes[cols - 1];
+
+//   return 0;
+// }
+
+// static int32_t mnodeRetrieveClusters(SShowObj *pShow, char *data, int32_t rows, void *pConn) {
+//   int32_t numOfRows = 0;
+//   int32_t cols = 0;
+//   char *  pWrite;
+//   SClusterObj *pCluster = NULL;
+
+//   while (numOfRows < rows) {
+//     pShow->pIter = mnodeGetNextCluster(pShow->pIter, &pCluster);
+//     if (pCluster == NULL) break;
+    
+//     cols = 0;
+
+//     pWrite = data + pShow->offset[cols] * rows + pShow->bytes[cols] * numOfRows;
+//     STR_WITH_MAXSIZE_TO_VARSTR(pWrite, pCluster->uid, TSDB_CLUSTER_ID_LEN);
+//     cols++;
+
+//     pWrite = data + pShow->offset[cols] * rows + pShow->bytes[cols] * numOfRows;
+//     *(int64_t *) pWrite = pCluster->createdTime;
+//     cols++;
+
+//     mnodeDecClusterRef(pCluster);
+//     numOfRows++;
+//   }
+
+//   mnodeVacuumResult(data, pShow->numOfColumns, numOfRows, rows, pShow);
+//   pShow->numOfReads += numOfRows;
+//   return numOfRows;
+// }
+
+// static void mnodeCancelGetNextCluster(void *pIter) {
+//   sdbFreeIter(tsClusterSdb, pIter);
+// }
+
 int32_t mndInitCluster(SMnode *pMnode) {
   SSdbTable table = {.sdbType = SDB_CLUSTER,
                      .keyType = SDB_KEY_INT32,
@@ -104,6 +170,9 @@ int32_t mndInitCluster(SMnode *pMnode) {
                      .updateFp = (SdbUpdateFp)mndClusterActionUpdate,
                      .deleteFp = (SdbDeleteFp)mndClusterActionDelete};
 
+  // mnodeAddShowMetaHandle(TSDB_MGMT_TABLE_CLUSTER, mnodeGetClusterMeta);
+  // mnodeAddShowRetrieveHandle(TSDB_MGMT_TABLE_CLUSTER, mnodeRetrieveClusters);
+  // mnodeAddShowFreeIterHandle(TSDB_MGMT_TABLE_CLUSTER, mnodeCancelGetNextCluster);
   return sdbSetTable(pMnode->pSdb, table);
 }
 
diff --git a/source/dnode/mnode/impl/src/mndConnect.c b/source/dnode/mnode/impl/src/mndConnect.c
new file mode 100644
index 0000000000000000000000000000000000000000..8e62eacfabf06c3c2fe74a8c4020b54d4c2f0b38
--- /dev/null
+++ b/source/dnode/mnode/impl/src/mndConnect.c
@@ -0,0 +1,155 @@
+/*
+ * Copyright (c) 2019 TAOS Data, Inc. <jhtao@taosdata.com>
+ *
+ * This program is free software: you can use, redistribute, and/or modify
+ * it under the terms of the GNU Affero General Public License, version 3
+ * or later ("AGPL"), as published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.
+ *
+ * You should have received a copy of the GNU Affero General Public License
+ * along with this program. If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#define _DEFAULT_SOURCE
+#include "mndShow.h"
+
+
+
+// static int32_t mnodeProcessHeartBeatMsg(SMnodeMsg *pMsg) {
+//   SHeartBeatRsp *pRsp = (SHeartBeatRsp *)rpcMallocCont(sizeof(SHeartBeatRsp));
+//   if (pRsp == NULL) {
+//     return TSDB_CODE_MND_OUT_OF_MEMORY;
+//   }
+
+//   SHeartBeatMsg *pHBMsg = pMsg->rpcMsg.pCont;
+//   if (taosCheckVersion(pHBMsg->clientVer, version, 3) != TSDB_CODE_SUCCESS) {
+//     rpcFreeCont(pRsp);
+//     return TSDB_CODE_TSC_INVALID_VERSION;  // todo change the error code
+//   }
+
+//   SRpcConnInfo connInfo = {0};
+//   rpcGetConnInfo(pMsg->rpcMsg.handle, &connInfo);
+    
+//   int32_t connId = htonl(pHBMsg->connId);
+//   SConnObj *pConn = mnodeAccquireConn(connId, connInfo.user, connInfo.clientIp, connInfo.clientPort);
+//   if (pConn == NULL) {
+//     pHBMsg->pid = htonl(pHBMsg->pid);
+//     pConn = mnodeCreateConn(connInfo.user, connInfo.clientIp, connInfo.clientPort, pHBMsg->pid, pHBMsg->appName);
+//   }
+
+//   if (pConn == NULL) {
+//     // do not close existing links, otherwise
+//     // mError("failed to create connId, close connect");
+//     // pRsp->killConnection = 1;    
+//   } else {
+//     pRsp->connId = htonl(pConn->connId);
+//     mnodeSaveQueryStreamList(pConn, pHBMsg);
+    
+//     if (pConn->killed != 0) {
+//       pRsp->killConnection = 1;
+//     }
+
+//     if (pConn->streamId != 0) {
+//       pRsp->streamId = htonl(pConn->streamId);
+//       pConn->streamId = 0;
+//     }
+
+//     if (pConn->queryId != 0) {
+//       pRsp->queryId = htonl(pConn->queryId);
+//       pConn->queryId = 0;
+//     }
+//   }
+
+//   int32_t    onlineDnodes = 0, totalDnodes = 0;
+//   mnodeGetOnlineAndTotalDnodesNum(&onlineDnodes, &totalDnodes);
+
+//   pRsp->onlineDnodes = htonl(onlineDnodes);
+//   pRsp->totalDnodes = htonl(totalDnodes);
+//   mnodeGetMnodeEpSetForShell(&pRsp->epSet, false);
+
+//   pMsg->rpcRsp.rsp = pRsp;
+//   pMsg->rpcRsp.len = sizeof(SHeartBeatRsp);
+
+//   mnodeReleaseConn(pConn);
+//   return TSDB_CODE_SUCCESS;
+// }
+
+// static int32_t mnodeProcessConnectMsg(SMnodeMsg *pMsg) {
+//   SConnectMsg *pConnectMsg = pMsg->rpcMsg.pCont;
+//   SConnectRsp *pConnectRsp = NULL;
+//   int32_t code = TSDB_CODE_SUCCESS;
+
+//   SRpcConnInfo connInfo = {0};
+//   if (rpcGetConnInfo(pMsg->rpcMsg.handle, &connInfo) != 0) {
+//     mError("thandle:%p is already released while process connect msg", pMsg->rpcMsg.handle);
+//     code = TSDB_CODE_MND_INVALID_CONNECTION;
+//     goto connect_over;
+//   }
+
+//   code = taosCheckVersion(pConnectMsg->clientVersion, version, 3);
+//   if (code != TSDB_CODE_SUCCESS) {
+//     goto connect_over;
+//   }
+
+//   SUserObj *pUser = pMsg->pUser;
+//   SAcctObj *pAcct = pUser->pAcct;
+
+//   if (pConnectMsg->db[0]) {
+//     char dbName[TSDB_TABLE_FNAME_LEN * 3] = {0};
+//     sprintf(dbName, "%x%s%s", pAcct->acctId, TS_PATH_DELIMITER, pConnectMsg->db);
+//     SDbObj *pDb = mnodeGetDb(dbName);
+//     if (pDb == NULL) {
+//       code = TSDB_CODE_MND_INVALID_DB;
+//       goto connect_over;
+//     }
+    
+//     if (pDb->status != TSDB_DB_STATUS_READY) {
+//       mError("db:%s, status:%d, in dropping", pDb->name, pDb->status);
+//       code = TSDB_CODE_MND_DB_IN_DROPPING;
+//       mnodeDecDbRef(pDb);
+//       goto connect_over;
+//     }
+//     mnodeDecDbRef(pDb);
+//   }
+
+//   pConnectRsp = rpcMallocCont(sizeof(SConnectRsp));
+//   if (pConnectRsp == NULL) {
+//     code = TSDB_CODE_MND_OUT_OF_MEMORY;
+//     goto connect_over;
+//   }
+
+//   pConnectMsg->pid = htonl(pConnectMsg->pid);
+//   SConnObj *pConn = mnodeCreateConn(connInfo.user, connInfo.clientIp, connInfo.clientPort, pConnectMsg->pid, pConnectMsg->appName);
+//   if (pConn == NULL) {
+//     code = terrno;
+//   } else {
+//     pConnectRsp->connId = htonl(pConn->connId);
+//     mnodeReleaseConn(pConn);
+//   }
+
+//   sprintf(pConnectRsp->acctId, "%x", pAcct->acctId);
+//   memcpy(pConnectRsp->serverVersion, version, TSDB_VERSION_LEN);
+//   pConnectRsp->writeAuth = pUser->writeAuth;
+//   pConnectRsp->superAuth = pUser->superAuth;
+  
+//   mnodeGetMnodeEpSetForShell(&pConnectRsp->epSet, false);
+
+//   dnodeGetClusterId(pConnectRsp->clusterId);
+
+// connect_over:
+//   if (code != TSDB_CODE_SUCCESS) {
+//     if (pConnectRsp) rpcFreeCont(pConnectRsp);
+//     mLError("user:%s login from %s, result:%s", connInfo.user, taosIpStr(connInfo.clientIp), tstrerror(code));
+//   } else {
+//     mLInfo("user:%s login from %s, result:%s", connInfo.user, taosIpStr(connInfo.clientIp), tstrerror(code));
+//     pMsg->rpcRsp.rsp = pConnectRsp;
+//     pMsg->rpcRsp.len = sizeof(SConnectRsp);
+//   }
+
+//   return code;
+// }
+
+
diff --git a/source/dnode/mnode/impl/src/mndDb.c b/source/dnode/mnode/impl/src/mndDb.c
index 3a5a2216775a311215a36410e44bb26789bba39d..0ad144d2dfc0e0d93dde661c507a6bb7c12f31e9 100644
--- a/source/dnode/mnode/impl/src/mndDb.c
+++ b/source/dnode/mnode/impl/src/mndDb.c
@@ -18,4 +18,22 @@
 #include "mndInt.h"
 
 int32_t mndInitDb(SMnode *pMnode) { return 0; }
-void    mndCleanupDb(SMnode *pMnode) {}
\ No newline at end of file
+void    mndCleanupDb(SMnode *pMnode) {}
+
+
+// static int32_t mnodeProcessUseMsg(SMnodeMsg *pMsg) {
+//   SUseDbMsg *pUseDbMsg = pMsg->rpcMsg.pCont;
+
+//   int32_t code = TSDB_CODE_SUCCESS;
+//   if (pMsg->pDb == NULL) pMsg->pDb = mnodeGetDb(pUseDbMsg->db);
+//   if (pMsg->pDb == NULL) {
+//     return TSDB_CODE_MND_INVALID_DB;
+//   }
+  
+//   if (pMsg->pDb->status != TSDB_DB_STATUS_READY) {
+//     mError("db:%s, status:%d, in dropping", pMsg->pDb->name, pMsg->pDb->status);
+//     return TSDB_CODE_MND_DB_IN_DROPPING;
+//   }
+
+//   return code;
+// }
diff --git a/source/dnode/mnode/impl/src/mndShow.c b/source/dnode/mnode/impl/src/mndShow.c
index 9938e95a7325a40103f531fc55c06d18f8da2f76..af6a2030064a09b5ea750ed01681b33b2adca605 100644
--- a/source/dnode/mnode/impl/src/mndShow.c
+++ b/source/dnode/mnode/impl/src/mndShow.c
@@ -14,8 +14,314 @@
  */
 
 #define _DEFAULT_SOURCE
-#include "os.h"
-#include "mndInt.h"
+#include "mndShow.h"
 
-int32_t mndInitShow(SMnode *pMnode) { return 0; }
-void    mndCleanupShow(SMnode *pMnode) {}
\ No newline at end of file
+static int32_t mndProcessShowMsg(SMnode *pMnode, SMnodeMsg *pMnodeMsg);
+static int32_t mndProcessRetrieveMsg(SMnode *pMnode, SMnodeMsg *pMsg);
+static bool    mndCheckRetrieveFinished(SShowObj *pShow);
+static int32_t mndAcquireShowObj(SMnode *pMnode, SShowObj *pShow);
+static void    mndReleaseShowObj(SShowObj *pShow, bool forceRemove);
+static int32_t mndPutShowObj(SMnode *pMnode, SShowObj *pShow);
+static void    mndFreeShowObj(void *ppShow);
+static char   *mndShowStr(int32_t showType);
+
+int32_t mndInitShow(SMnode *pMnode) {
+  SShowMgmt *pMgmt = &pMnode->showMgmt;
+
+  pMgmt->cache = taosCacheInit(TSDB_CACHE_PTR_KEY, 5, true, mndFreeShowObj, "show");
+  if (pMgmt->cache == NULL) {
+    terrno = TSDB_CODE_OUT_OF_MEMORY;
+    mError("failed to alloc show cache since %s", terrstr());
+    return -1;
+  }
+
+  mndSetMsgHandle(pMnode, TSDB_MSG_TYPE_SHOW, mndProcessShowMsg);
+  mndSetMsgHandle(pMnode, TSDB_MSG_TYPE_SHOW_RETRIEVE, mndProcessRetrieveMsg);
+  return 0;
+}
+
+void mndCleanupShow(SMnode *pMnode) {}
+
+static int32_t mndProcessShowMsg(SMnode *pMnode, SMnodeMsg *pMnodeMsg) {
+  SShowMgmt *pMgmt = &pMnode->showMgmt;
+  SShowMsg  *pMsg = pMnodeMsg->rpcMsg.pCont;
+  int8_t     type = pMsg->type;
+  uint16_t   payloadLen = htonl(pMsg->payloadLen);
+
+  if (type <= TSDB_MGMT_TABLE_START || type >= TSDB_MGMT_TABLE_MAX) {
+    terrno = TSDB_CODE_MND_INVALID_MSG_TYPE;
+    mError("failed to process show msg since %s", terrstr());
+    return -1;
+  }
+
+  ShowMetaFp metaFp = pMgmt->metaFps[type];
+  if (metaFp == NULL) {
+    terrno = TSDB_CODE_MND_INVALID_MSG_TYPE;
+    mError("failed to process show-meta msg:%s since no message handle", mndShowStr(type));
+    return -1;
+  }
+
+  int32_t   size = sizeof(SShowObj) + payloadLen;
+  SShowObj *pShow = calloc(1, size);
+  if (pShow != NULL) {
+    pShow->pMnode = pMnode;
+    pShow->type = type;
+    pShow->payloadLen = payloadLen;
+    memcpy(pShow->db, pMsg->db, TSDB_FULL_DB_NAME_LEN);
+    memcpy(pShow->payload, pMsg->payload, payloadLen);
+  } else {
+    terrno = TSDB_CODE_OUT_OF_MEMORY;
+    mError("failed to process show-meta msg:%s since %s", mndShowStr(type), terrstr());
+    return -1;
+  }
+
+  if (mndPutShowObj(pMnode, pShow) == 0) {
+    mError("failed to process show-meta msg:%s since %s", mndShowStr(type), terrstr());
+    free(pShow);
+    return -1;
+  }
+
+  size = sizeof(SShowRsp) + sizeof(SSchema) * TSDB_MAX_COLUMNS + TSDB_EXTRA_PAYLOAD_SIZE;
+  SShowRsp *pRsp = rpcMallocCont(size);
+  if (pRsp == NULL) {
+    mndReleaseShowObj(pShow, true);
+    terrno = TSDB_CODE_OUT_OF_MEMORY;
+    mError("show:%d, failed to process show-meta msg:%s since malloc rsp error", pShow->id, mndShowStr(type));
+    return -1;
+  }
+
+  pRsp->qhandle = htobe64((uint64_t)pShow);
+
+  int32_t code = (*metaFp)(pMnode, &pRsp->tableMeta, pShow, pMnodeMsg->rpcMsg.handle);
+  mDebug("show:%d, type:%s, get meta finished, numOfRows:%d cols:%d result:%s", pShow->id, mndShowStr(type),
+         pShow->numOfRows, pShow->numOfColumns, tstrerror(code));
+
+  if (code == TSDB_CODE_SUCCESS) {
+    pMnodeMsg->contLen = sizeof(SShowRsp) + sizeof(SSchema) * pShow->numOfColumns;
+    pMnodeMsg->pCont = pRsp;
+    mndReleaseShowObj(pShow, false);
+    return TSDB_CODE_SUCCESS;
+  } else {
+    rpcFreeCont(pRsp);
+    mndReleaseShowObj(pShow, true);
+    return code;
+  }
+}
+
+static int32_t mndProcessRetrieveMsg(SMnode *pMnode, SMnodeMsg *pMnodeMsg) {
+  SShowMgmt *pMgmt = &pMnode->showMgmt;
+  int32_t    rowsToRead = 0;
+  int32_t    size = 0;
+  int32_t    rowsRead = 0;
+
+  SRetrieveTableMsg *pRetrieve = pMnodeMsg->rpcMsg.pCont;
+  pRetrieve->qhandle = htobe64(pRetrieve->qhandle);
+  SShowObj *pShow = (SShowObj *)pRetrieve->qhandle;
+
+  /*
+   * in case of server restart, apps may hold qhandle created by server before
+   * restart, which is actually invalid, therefore, signature check is required.
+   */
+  if (mndAcquireShowObj(pMnode, pShow) != 0) {
+    terrno = TSDB_CODE_MND_INVALID_SHOWOBJ;
+    mError("failed to process show-retrieve msg:%p since %s", pShow, terrstr());
+    return -1;
+  }
+
+  ShowRetrieveFp retrieveFp = pMgmt->retrieveFps[pShow->type];
+  if (retrieveFp == NULL) {
+    mndReleaseShowObj(pShow, false);
+    terrno = TSDB_CODE_MSG_NOT_PROCESSED;
+    mError("show:%d, failed to retrieve data since %s", pShow->id, terrstr());
+    return -1;
+  }
+
+  mDebug("show:%d, type:%s, start retrieve data, numOfReads:%d numOfRows:%d", pShow->id, mndShowStr(pShow->type),
+         pShow->numOfReads, pShow->numOfRows);
+
+  if (mndCheckRetrieveFinished(pShow)) {
+    mDebug("show:%d, read finished, numOfReads:%d numOfRows:%d", pShow->id, pShow->numOfReads, pShow->numOfRows);
+    pShow->numOfReads = pShow->numOfRows;
+  }
+
+  if ((pRetrieve->free & TSDB_QUERY_TYPE_FREE_RESOURCE) != TSDB_QUERY_TYPE_FREE_RESOURCE) {
+    rowsToRead = pShow->numOfRows - pShow->numOfReads;
+  }
+
+  /* return no more than 100 tables in one round trip */
+  if (rowsToRead > 100) rowsToRead = 100;
+
+  /*
+   * the actual number of table may be larger than the value of pShow->numOfRows, if a query is
+   * issued during a continuous create table operation. Therefore, rowToRead may be less than 0.
+   */
+  if (rowsToRead < 0) rowsToRead = 0;
+  size = pShow->rowSize * rowsToRead;
+
+  size += 100;
+  SRetrieveTableRsp *pRsp = rpcMallocCont(size);
+  if (pRsp == NULL) {
+    mndReleaseShowObj(pShow, false);
+    terrno = TSDB_CODE_OUT_OF_MEMORY;
+    mError("show:%d, failed to retrieve data since %s", pShow->id, terrstr());
+    return -1;
+  }
+
+  // if free flag is set, client wants to clean the resources
+  if ((pRetrieve->free & TSDB_QUERY_TYPE_FREE_RESOURCE) != TSDB_QUERY_TYPE_FREE_RESOURCE) {
+    rowsRead = (*retrieveFp)(pMnode, pShow, pRsp->data, rowsToRead, pMnodeMsg->rpcMsg.handle);
+  }
+
+  mDebug("show:%d, stop retrieve data, rowsRead:%d rowsToRead:%d", pShow->id, rowsRead, rowsToRead);
+
+  pRsp->numOfRows = htonl(rowsRead);
+  pRsp->precision = (int16_t)htonl(TSDB_TIME_PRECISION_MILLI);  // millisecond time precision
+
+  pMnodeMsg->pCont = pRsp;
+  pMnodeMsg->contLen = size;
+
+  if (rowsToRead == 0 || (rowsRead == rowsToRead && pShow->numOfRows == pShow->numOfReads)) {
+    pRsp->completed = 1;
+    mDebug("%p, retrieve completed", pShow);
+    mndReleaseShowObj(pShow, true);
+  } else {
+    mDebug("%p, retrieve not completed yet", pShow);
+    mndReleaseShowObj(pShow, false);
+  }
+
+  return TSDB_CODE_SUCCESS;
+}
+
+static char *mndShowStr(int32_t showType) {
+  switch (showType) {
+    case TSDB_MGMT_TABLE_ACCT:
+      return "show accounts";
+    case TSDB_MGMT_TABLE_USER:
+      return "show users";
+    case TSDB_MGMT_TABLE_DB:
+      return "show databases";
+    case TSDB_MGMT_TABLE_TABLE:
+      return "show tables";
+    case TSDB_MGMT_TABLE_DNODE:
+      return "show dnodes";
+    case TSDB_MGMT_TABLE_MNODE:
+      return "show mnodes";
+    case TSDB_MGMT_TABLE_VGROUP:
+      return "show vgroups";
+    case TSDB_MGMT_TABLE_METRIC:
+      return "show stables";
+    case TSDB_MGMT_TABLE_MODULE:
+      return "show modules";
+    case TSDB_MGMT_TABLE_QUERIES:
+      return "show queries";
+    case TSDB_MGMT_TABLE_STREAMS:
+      return "show streams";
+    case TSDB_MGMT_TABLE_VARIABLES:
+      return "show configs";
+    case TSDB_MGMT_TABLE_CONNS:
+      return "show connections";
+    case TSDB_MGMT_TABLE_SCORES:
+      return "show scores";
+    case TSDB_MGMT_TABLE_GRANTS:
+      return "show grants";
+    case TSDB_MGMT_TABLE_VNODES:
+      return "show vnodes";
+    case TSDB_MGMT_TABLE_CLUSTER:
+      return "show clusters";
+    case TSDB_MGMT_TABLE_STREAMTABLES:
+      return "show streamtables";
+    case TSDB_MGMT_TABLE_TP:
+      return "show topics";
+    default:
+      return "undefined";
+  }
+}
+
+static bool mndCheckRetrieveFinished(SShowObj *pShow) {
+  if (pShow->pIter == NULL && pShow->numOfReads != 0) {
+    return true;
+  } 
+  return false;
+}
+
+static int32_t mndAcquireShowObj(SMnode *pMnode, SShowObj *pShow) {
+  TSDB_CACHE_PTR_TYPE handleVal = (TSDB_CACHE_PTR_TYPE)pShow;
+
+  SShowMgmt *pMgmt = &pMnode->showMgmt;
+  SShowObj **ppShow = taosCacheAcquireByKey(pMgmt->cache, &handleVal, sizeof(TSDB_CACHE_PTR_TYPE));
+  if (ppShow) {
+    mTrace("show:%d, data:%p acquired from cache", pShow->id, ppShow);
+    return 0;
+  }
+
+  return -1;
+}
+
+static void mndReleaseShowObj(SShowObj *pShow, bool forceRemove) {
+  SMnode    *pMnode = pShow->pMnode;
+  SShowMgmt *pMgmt = &pMnode->showMgmt;
+  SShowObj **ppShow = (SShowObj **)pShow->ppShow;
+  taosCacheRelease(pMgmt->cache, (void **)(&ppShow), forceRemove);
+  mDebug("show:%d, data:%p released from cache, force:%d", pShow->id, ppShow, forceRemove);
+}
+
+static int32_t mndPutShowObj(SMnode *pMnode, SShowObj *pShow) {
+  SShowMgmt *pMgmt = &pMnode->showMgmt;
+  int32_t    lifeSpan = pMnode->shellActivityTimer * 6 * 1000;
+
+  TSDB_CACHE_PTR_TYPE val = (TSDB_CACHE_PTR_TYPE)pShow;
+  pShow->id = atomic_add_fetch_32(&pMgmt->showId, 1);
+  SShowObj **ppShow =
+      taosCachePut(pMgmt->cache, &val, sizeof(TSDB_CACHE_PTR_TYPE), &pShow, sizeof(TSDB_CACHE_PTR_TYPE), lifeSpan);
+  if (ppShow == NULL) {
+    terrno = TSDB_CODE_OUT_OF_MEMORY;
+    mError("show:%d, failed to put into cache", pShow->id);
+    return -1;
+  }
+
+  mTrace("show:%d, data:%p put into cache", pShow->id, ppShow);
+  return 0;
+}
+
+static void mndFreeShowObj(void *ppShow) {
+  SShowObj  *pShow = *(SShowObj **)ppShow;
+  SMnode    *pMnode = pShow->pMnode;
+  SShowMgmt *pMgmt = &pMnode->showMgmt;
+
+  ShowFreeIterFp freeFp = pMgmt->freeIterFps[pShow->type];
+  if (freeFp != NULL) {
+    if (pShow->pVgIter != NULL) {
+      // only used in 'show vnodes "ep"'
+      (*freeFp)(pMnode, pShow->pVgIter);
+    }
+    if (pShow->pIter != NULL) {
+      (*freeFp)(pMnode, pShow->pIter);
+    }
+  }
+
+  mDebug("show:%d, data:%p destroyed", pShow->id, ppShow);
+  tfree(pShow);
+}
+
+void mnodeVacuumResult(char *data, int32_t numOfCols, int32_t rows, int32_t capacity, SShowObj *pShow) {
+  if (rows < capacity) {
+    for (int32_t i = 0; i < numOfCols; ++i) {
+      memmove(data + pShow->offset[i] * rows, data + pShow->offset[i] * capacity, pShow->bytes[i] * rows);
+    }
+  }
+}
+
+void mnodeAddShowMetaHandle(SMnode *pMnode, EShowType showType, ShowMetaFp fp) {
+  SShowMgmt *pMgmt = &pMnode->showMgmt;
+  pMgmt->metaFps[showType] = fp;
+}
+
+void mnodeAddShowRetrieveHandle(SMnode *pMnode, EShowType showType, ShowRetrieveFp fp) {
+  SShowMgmt *pMgmt = &pMnode->showMgmt;
+  pMgmt->retrieveFps[showType] = fp;
+}
+
+void mnodeAddShowFreeIterHandle(SMnode *pMnode, EShowType showType, ShowFreeIterFp fp) {
+  SShowMgmt *pMgmt = &pMnode->showMgmt;
+  pMgmt->freeIterFps[showType] = fp;
+}