diff --git a/rdsn b/rdsn
index 0ccfd9736d..16addfc0ad 160000
--- a/rdsn
+++ b/rdsn
@@ -1 +1 @@
-Subproject commit 0ccfd9736d2fc950df99b860a0e55f61a9d33de6
+Subproject commit 16addfc0ada004cab3b7366fc46f9b93319d989d
diff --git a/src/shell/commands.h b/src/shell/commands.h
index 7ce27982e0..19be0d00bd 100644
--- a/src/shell/commands.h
+++ b/src/shell/commands.h
@@ -4310,3 +4310,232 @@ inline bool clear_app_envs(command_executor *e, shell_context *sc, arguments arg
     }
     return true;
 }
+
+inline dsn::rpc_address diagnose_recommend(const ddd_partition_info &pinfo)
+{
+    if (pinfo.config.last_drops.size() < 2)
+        return dsn::rpc_address();
+
+    std::vector<dsn::rpc_address> last_two_nodes(pinfo.config.last_drops.end() - 2,
+                                                 pinfo.config.last_drops.end());
+    std::vector<ddd_node_info> last_dropped;
+    for (auto &node : last_two_nodes) {
+        auto it = std::find_if(pinfo.dropped.begin(),
+                               pinfo.dropped.end(),
+                               [&node](const ddd_node_info &r) { return r.node == node; });
+        if (it->is_alive && it->is_collected)
+            last_dropped.push_back(*it);
+    }
+
+    if (last_dropped.size() == 1) {
+        const ddd_node_info &ninfo = last_dropped.back();
+        if (ninfo.last_committed_decree >= pinfo.config.last_committed_decree)
+            return ninfo.node;
+    } else if (last_dropped.size() == 2) {
+        const ddd_node_info &secondary = last_dropped.front();
+        const ddd_node_info &latest = last_dropped.back();
+
+        // Select a best node to be the new primary, following the rule:
+        //  - choose the node with the largest last committed decree
+        //  - if last committed decree is the same, choose node with the largest ballot
+
+        if (latest.last_committed_decree == secondary.last_committed_decree &&
+            latest.last_committed_decree >= pinfo.config.last_committed_decree)
+            return latest.ballot >= secondary.ballot ? latest.node : secondary.node;
+
+        if (latest.last_committed_decree > secondary.last_committed_decree &&
+            latest.last_committed_decree >= pinfo.config.last_committed_decree)
+            return latest.node;
+
+        if (secondary.last_committed_decree > latest.last_committed_decree &&
+            secondary.last_committed_decree >= pinfo.config.last_committed_decree)
+            return secondary.node;
+    }
+
+    return dsn::rpc_address();
+}
+
+inline bool ddd_diagnose(command_executor *e, shell_context *sc, arguments args)
+{
+    static struct option long_options[] = {{"gpid", required_argument, 0, 'g'},
+                                           {"diagnose", no_argument, 0, 'd'},
+                                           {"auto_diagnose", no_argument, 0, 'a'},
+                                           {"skip_prompt", no_argument, 0, 's'},
+                                           {"output", required_argument, 0, 'o'},
+                                           {0, 0, 0, 0}};
+
+    std::string out_file;
+    dsn::gpid id(-1, -1);
+    bool diagnose = false;
+    bool auto_diagnose = false;
+    bool skip_prompt = false;
+    optind = 0;
+    while (true) {
+        int option_index = 0;
+        int c;
+        c = getopt_long(args.argc, args.argv, "g:daso:", long_options, &option_index);
+        if (c == -1)
+            break;
+        switch (c) {
+        case 'g':
+            int pid;
+            if (id.parse_from(optarg)) {
+                // app_id.partition_index
+            } else if (sscanf(optarg, "%d", &pid) == 1) {
+                // app_id
+                id.set_app_id(pid);
+            } else {
+                fprintf(stderr, "ERROR: invalid gpid %s\n", optarg);
+                return false;
+            }
+            break;
+        case 'd':
+            diagnose = true;
+            break;
+        case 'a':
+            auto_diagnose = true;
+            break;
+        case 's':
+            skip_prompt = true;
+            break;
+        case 'o':
+            out_file = optarg;
+            break;
+        default:
+            return false;
+        }
+    }
+
+    std::vector<ddd_partition_info> ddd_partitions;
+    ::dsn::error_code ret = sc->ddl_client->ddd_diagnose(id, ddd_partitions);
+    if (ret != dsn::ERR_OK) {
+        fprintf(stderr, "ERROR: DDD diagnose failed with err = %s\n", ret.to_string());
+        return true;
+    }
+
+    std::streambuf *buf;
+    std::ofstream of;
+
+    if (!out_file.empty()) {
+        of.open(out_file);
+        buf = of.rdbuf();
+    } else {
+        buf = std::cout.rdbuf();
+    }
+    std::ostream out(buf);
+
+    out << "Total " << ddd_partitions.size() << " ddd partitions:" << std::endl;
+    out << std::endl;
+    int proposed_count = 0;
+    int i = 0;
+    for (const ddd_partition_info &pinfo : ddd_partitions) {
+        out << "(" << ++i << ") " << pinfo.config.pid.to_string() << std::endl;
+        out << "    config: ballot(" << pinfo.config.ballot << "), "
+            << "last_committed(" << pinfo.config.last_committed_decree << ")" << std::endl;
+        out << "    ----" << std::endl;
+        dsn::rpc_address latest_dropped, secondary_latest_dropped;
+        if (pinfo.config.last_drops.size() > 0)
+            latest_dropped = pinfo.config.last_drops[pinfo.config.last_drops.size() - 1];
+        if (pinfo.config.last_drops.size() > 1)
+            secondary_latest_dropped = pinfo.config.last_drops[pinfo.config.last_drops.size() - 2];
+        int j = 0;
+        for (const ddd_node_info &n : pinfo.dropped) {
+            char time_buf[30];
+            ::dsn::utils::time_ms_to_string(n.drop_time_ms, time_buf);
+            out << "    dropped[" << j++ << "]: "
+                << "node(" << n.node.to_string() << "), "
+                << "drop_time(" << time_buf << "), "
+                << "alive(" << (n.is_alive ? "true" : "false") << "), "
+                << "collected(" << (n.is_collected ? "true" : "false") << "), "
+                << "ballot(" << n.ballot << "), "
+                << "last_committed(" << n.last_committed_decree << "), "
+                << "last_prepared(" << n.last_prepared_decree << ")";
+            if (n.node == latest_dropped)
+                out << "  <== the latest";
+            else if (n.node == secondary_latest_dropped)
+                out << "  <== the secondary latest";
+            out << std::endl;
+        }
+        out << "    ----" << std::endl;
+        j = 0;
+        for (const ::dsn::rpc_address &r : pinfo.config.last_drops) {
+            out << "    last_drops[" << j++ << "]: "
+                << "node(" << r.to_string() << ")";
+            if (j == (int)pinfo.config.last_drops.size() - 1)
+                out << "  <== the secondary latest";
+            else if (j == (int)pinfo.config.last_drops.size())
+                out << "  <== the latest";
+            out << std::endl;
+        }
+        out << "    ----" << std::endl;
+        out << "    ddd_reason: " << pinfo.reason << std::endl;
+        if (diagnose) {
+            out << "    ----" << std::endl;
+
+            dsn::rpc_address primary = diagnose_recommend(pinfo);
+            out << "    recommend_primary: "
+                << (primary.is_invalid() ? "none" : primary.to_string());
+            if (primary == latest_dropped)
+                out << "  <== the latest";
+            else if (primary == secondary_latest_dropped)
+                out << "  <== the secondary latest";
+            out << std::endl;
+
+            bool skip_this = false;
+            if (!primary.is_invalid() && !auto_diagnose && !skip_prompt) {
+                do {
+                    std::cout << "    > Are you sure to use the recommend primary? [y/n/s(skip)]: ";
+                    char c;
+                    std::cin >> c;
+                    if (c == 'y') {
+                        break;
+                    } else if (c == 'n') {
+                        primary.set_invalid();
+                        break;
+                    } else if (c == 's') {
+                        skip_this = true;
+                        std::cout << "    > You have choosed to skip diagnosing this partition."
+                                  << std::endl;
+                        break;
+                    }
+                } while (true);
+            }
+
+            if (primary.is_invalid() && !skip_prompt && !skip_this) {
+                do {
+                    std::cout << "    > Please input the primary node: ";
+                    std::string addr;
+                    std::cin >> addr;
+                    if (primary.from_string_ipv4(addr.c_str())) {
+                        break;
+                    } else {
+                        std::cout << "    > Sorry, you have input an invalid node address."
+                                  << std::endl;
+                    }
+                } while (true);
+            }
+
+            if (!primary.is_invalid() && !skip_this) {
+                dsn::replication::configuration_balancer_request request;
+                request.gpid = pinfo.config.pid;
+                request.action_list = {configuration_proposal_action{
+                    primary, primary, config_type::CT_ASSIGN_PRIMARY}};
+                request.force = false;
+                dsn::error_code err = sc->ddl_client->send_balancer_proposal(request);
+                out << "    propose_request: propose -g " << request.gpid.to_string()
+                    << " -p ASSIGN_PRIMARY -t " << primary.to_string() << " -n "
+                    << primary.to_string() << std::endl;
+                out << "    propose_response: " << err.to_string() << std::endl;
+                proposed_count++;
+            } else {
+                out << "    propose_request: none" << std::endl;
+            }
+        }
+        out << std::endl;
+        out << "Proposed count: " << proposed_count << "/" << ddd_partitions.size() << std::endl;
+        out << std::endl;
+    }
+
+    std::cout << "Diagnose ddd done." << std::endl;
+    return true;
+}
diff --git a/src/shell/main.cpp b/src/shell/main.cpp
index ba84d3850b..47ef35b8a8 100644
--- a/src/shell/main.cpp
+++ b/src/shell/main.cpp
@@ -375,7 +375,14 @@ static command_executor commands[] = {
         "del_app_envs", "delete current app envs", "<key> [key...]", del_app_envs,
     },
     {
-        "clear_app_envs", "clear current app envs", "<-a|--all> <-p|--prefix str>", clear_app_envs,
+        "clear_app_envs", "clear current app envs", "[-a|--all] [-p|--prefix str]", clear_app_envs,
+    },
+    {
+        "ddd_diagnose",
+        "diagnose three-dead partitions",
+        "[-g|--gpid appid|appid.pidx] [-d|--diagnose] [-a|--auto_diagnose] "
+        "[-s|--skip_prompt] [-o|--output file_name]",
+        ddd_diagnose,
     },
     {
         "exit", "exit shell", "", exit_shell,