check 2 mnode

include/util/taoserror.h

@@ -406,6 +406,7 @@ int32_t* taosGetErrno();
 #define TSDB_CODE_SNODE_NOT_DEPLOYED            TAOS_DEF_ERROR_CODE(0, 0x0411)
 #define TSDB_CODE_MNODE_NOT_CATCH_UP            TAOS_DEF_ERROR_CODE(0, 0x0412) // internal
 #define TSDB_CODE_MNODE_ALREADY_IS_VOTER        TAOS_DEF_ERROR_CODE(0, 0x0413) // internal
+#define TSDB_CODE_MNODE_ONLY_TWO_MNODE          TAOS_DEF_ERROR_CODE(0, 0x0414) // internal
 
 // vnode
 // #define TSDB_CODE_VND_ACTION_IN_PROGRESS     TAOS_DEF_ERROR_CODE(0, 0x0500) // 2.x

source/dnode/mnode/impl/src/mndDnode.c

@@ -612,6 +612,13 @@ static int32_t mndRestoreDnode(SMnode *pMnode, SRpcMsg *pReq, SDnodeObj *pDnode,
 
   if(restoreType == RESTORE_TYPE__ALL || restoreType == RESTORE_TYPE__MNODE)
   {
+    int32_t totalMnodes = sdbGetSize(pMnode->pSdb, SDB_MNODE);
+    if (totalMnodes == 2) {
+        mError("cant't restore mnode, since a mnode on it and replica is 2");
+        terrno = TSDB_CODE_MNODE_ONLY_TWO_MNODE;
+        return -1;
+    }
+    
     SMnodeObj *mnodeObj = mndAcquireMnode(pMnode, pDnode->id);
     if(mnodeObj == NULL){
       mError("trans:%d, no mnode exist on dnode:%s", pTrans->id, pDnode->ep);

source/util/src/terror.c

@@ -320,6 +320,9 @@ TAOS_DEFINE_ERROR(TSDB_CODE_QNODE_NOT_DEPLOYED,           "Qnode not deployed")
 TAOS_DEFINE_ERROR(TSDB_CODE_SNODE_NOT_FOUND,              "Snode not found")
 TAOS_DEFINE_ERROR(TSDB_CODE_SNODE_ALREADY_DEPLOYED,       "Snode already deployed")
 TAOS_DEFINE_ERROR(TSDB_CODE_SNODE_NOT_DEPLOYED,           "Snode not deployed")
+TAOS_DEFINE_ERROR(TSDB_CODE_MNODE_NOT_CATCH_UP,           "Mnode didn't catch the leader")
+TAOS_DEFINE_ERROR(TSDB_CODE_MNODE_ALREADY_IS_VOTER,       "Mnode already is a leader")
+TAOS_DEFINE_ERROR(TSDB_CODE_MNODE_ONLY_TWO_MNODE,         "Only two mnodes exist")
 
 // vnode
 TAOS_DEFINE_ERROR(TSDB_CODE_VND_INVALID_VGROUP_ID,        "Vnode is closed or removed")