diff --git a/docs/en/14-reference/03-taos-sql/21-node.md b/docs/en/14-reference/03-taos-sql/21-node.md
index 2ebccb76f7..cdc4bdd020 100644
--- a/docs/en/14-reference/03-taos-sql/21-node.md
+++ b/docs/en/14-reference/03-taos-sql/21-node.md
@@ -27,11 +27,15 @@ The preceding SQL command shows all dnodes in the cluster with the ID, endpoint,
 ## Delete a DNODE
 
 ```sql
-DROP DNODE dnode_id
+DROP DNODE dnode_id [force] [unsafe]
 ```
 
 Note that deleting a dnode does not stop its process. You must stop the process after the dnode is deleted.
 
+Only online node is allowed to be deleted. Drop is executed with force option if the offline node need to be deleted.
+
+Drop is executed with unsafe option if the node with single replica is offline, and the data on it is not able to be restored.
+
 ## Modify Dnode Configuration
 
 ```sql
diff --git a/docs/examples/java/src/main/java/com/taos/example/ConsumerLoopFull.java b/docs/examples/java/src/main/java/com/taos/example/ConsumerLoopFull.java
index a399f3aa6a..647855dc48 100644
--- a/docs/examples/java/src/main/java/com/taos/example/ConsumerLoopFull.java
+++ b/docs/examples/java/src/main/java/com/taos/example/ConsumerLoopFull.java
@@ -1,8 +1,9 @@
 package com.taos.example;
 
-import com.alibaba.fastjson.JSON;
+import com.fasterxml.jackson.core.JsonProcessingException;
 import com.taosdata.jdbc.TSDBDriver;
 import com.taosdata.jdbc.tmq.*;
+import com.taosdata.jdbc.utils.JsonUtil;
 
 import java.sql.*;
 import java.time.Duration;
@@ -60,7 +61,7 @@ public class ConsumerLoopFull {
 // ANCHOR_END: create_consumer
     }
 
-    public static void pollExample(TaosConsumer<ResultBean> consumer) throws SQLException {
+    public static void pollExample(TaosConsumer<ResultBean> consumer) throws SQLException, JsonProcessingException {
 // ANCHOR: poll_data_code_piece
         List<String> topics = Collections.singletonList("topic_meters");
         try {
@@ -73,7 +74,7 @@ public class ConsumerLoopFull {
                 for (ConsumerRecord<ResultBean> record : records) {
                     ResultBean bean = record.value();
                     // Add your data processing logic here
-                    System.out.println("data: " + JSON.toJSONString(bean));
+                    System.out.println("data: " + JsonUtil.getObjectMapper().writeValueAsString(bean));
                 }
             }
         } catch (Exception ex) {
@@ -91,7 +92,7 @@ public class ConsumerLoopFull {
 // ANCHOR_END: poll_data_code_piece
     }
 
-    public static void seekExample(TaosConsumer<ResultBean> consumer) throws SQLException {
+    public static void seekExample(TaosConsumer<ResultBean> consumer) throws SQLException, JsonProcessingException {
 // ANCHOR: consumer_seek
         List<String> topics = Collections.singletonList("topic_meters");
         try {
@@ -99,7 +100,7 @@ public class ConsumerLoopFull {
             consumer.subscribe(topics);
             System.out.println("Subscribe topics successfully.");
             Set<TopicPartition> assignment = consumer.assignment();
-            System.out.println("Now assignment: " + JSON.toJSONString(assignment));
+            System.out.println("Now assignment: " + JsonUtil.getObjectMapper().writeValueAsString(assignment));
 
             ConsumerRecords<ResultBean> records = ConsumerRecords.emptyRecord();
             // make sure we have got some data
@@ -125,7 +126,7 @@ public class ConsumerLoopFull {
     }
 
 
-    public static void commitExample(TaosConsumer<ResultBean> consumer) throws SQLException {
+    public static void commitExample(TaosConsumer<ResultBean> consumer) throws SQLException, JsonProcessingException {
 // ANCHOR: commit_code_piece
         List<String> topics = Collections.singletonList("topic_meters");
         try {
@@ -135,7 +136,7 @@ public class ConsumerLoopFull {
                 for (ConsumerRecord<ResultBean> record : records) {
                     ResultBean bean = record.value();
                     // Add your data processing logic here
-                    System.out.println("data: " + JSON.toJSONString(bean));
+                    System.out.println("data: " + JsonUtil.getObjectMapper().writeValueAsString(bean));
                 }
                 if (!records.isEmpty()) {
                     // after processing the data, commit the offset manually
diff --git a/docs/examples/java/src/main/java/com/taos/example/ConsumerLoopImp.java b/docs/examples/java/src/main/java/com/taos/example/ConsumerLoopImp.java
index a59bfc282f..378ef8ae6d 100644
--- a/docs/examples/java/src/main/java/com/taos/example/ConsumerLoopImp.java
+++ b/docs/examples/java/src/main/java/com/taos/example/ConsumerLoopImp.java
@@ -1,7 +1,7 @@
 package com.taos.example;
 
-import com.alibaba.fastjson.JSON;
 import com.taosdata.jdbc.TSDBDriver;
+import com.taosdata.jdbc.utils.JsonUtil;
 
 import java.sql.Connection;
 import java.sql.DriverManager;
@@ -31,7 +31,11 @@ public class ConsumerLoopImp {
         final AbsConsumerLoop consumerLoop = new AbsConsumerLoop() {
             @Override
             public void process(ResultBean result) {
-                System.out.println("data: " + JSON.toJSONString(result));
+                try{
+                    System.out.println("data: " + JsonUtil.getObjectMapper().writeValueAsString(result));
+                } catch (Exception e) {
+                    throw new RuntimeException(e);
+                }
             }
         };
 
diff --git a/docs/examples/java/src/main/java/com/taos/example/WsConsumerLoopFull.java b/docs/examples/java/src/main/java/com/taos/example/WsConsumerLoopFull.java
index 6db65f47f2..02db97a5a9 100644
--- a/docs/examples/java/src/main/java/com/taos/example/WsConsumerLoopFull.java
+++ b/docs/examples/java/src/main/java/com/taos/example/WsConsumerLoopFull.java
@@ -1,8 +1,9 @@
 package com.taos.example;
 
-import com.alibaba.fastjson.JSON;
+import com.fasterxml.jackson.core.JsonProcessingException;
 import com.taosdata.jdbc.TSDBDriver;
 import com.taosdata.jdbc.tmq.*;
+import com.taosdata.jdbc.utils.JsonUtil;
 
 import java.sql.*;
 import java.time.Duration;
@@ -60,7 +61,7 @@ public class WsConsumerLoopFull {
 // ANCHOR_END: create_consumer
     }
 
-    public static void pollExample(TaosConsumer<ResultBean> consumer) throws SQLException {
+    public static void pollExample(TaosConsumer<ResultBean> consumer) throws SQLException, JsonProcessingException {
 // ANCHOR: poll_data_code_piece
         List<String> topics = Collections.singletonList("topic_meters");
         try {
@@ -73,7 +74,7 @@ public class WsConsumerLoopFull {
                 for (ConsumerRecord<ResultBean> record : records) {
                     ResultBean bean = record.value();
                     // Add your data processing logic here
-                    System.out.println("data: " + JSON.toJSONString(bean));
+                    System.out.println("data: " + JsonUtil.getObjectMapper().writeValueAsString(bean));
                 }
             }
         } catch (Exception ex) {
@@ -91,7 +92,7 @@ public class WsConsumerLoopFull {
 // ANCHOR_END: poll_data_code_piece
     }
 
-    public static void seekExample(TaosConsumer<ResultBean> consumer) throws SQLException {
+    public static void seekExample(TaosConsumer<ResultBean> consumer) throws SQLException, JsonProcessingException {
 // ANCHOR: consumer_seek
         List<String> topics = Collections.singletonList("topic_meters");
         try {
@@ -99,7 +100,7 @@ public class WsConsumerLoopFull {
             consumer.subscribe(topics);
             System.out.println("Subscribe topics successfully.");
             Set<TopicPartition> assignment = consumer.assignment();
-            System.out.println("Now assignment: " + JSON.toJSONString(assignment));
+            System.out.println("Now assignment: " + JsonUtil.getObjectMapper().writeValueAsString(assignment));
 
             ConsumerRecords<ResultBean> records = ConsumerRecords.emptyRecord();
             // make sure we have got some data
@@ -125,7 +126,7 @@ public class WsConsumerLoopFull {
     }
 
 
-    public static void commitExample(TaosConsumer<ResultBean> consumer) throws SQLException {
+    public static void commitExample(TaosConsumer<ResultBean> consumer) throws SQLException, JsonProcessingException {
 // ANCHOR: commit_code_piece
         List<String> topics = Collections.singletonList("topic_meters");
         try {
@@ -135,7 +136,7 @@ public class WsConsumerLoopFull {
                 for (ConsumerRecord<ResultBean> record : records) {
                     ResultBean bean = record.value();
                     // Add your data processing logic here
-                    System.out.println("data: " + JSON.toJSONString(bean));
+                    System.out.println("data: " + JsonUtil.getObjectMapper().writeValueAsString(bean));
                 }
                 if (!records.isEmpty()) {
                     // after processing the data, commit the offset manually
diff --git a/docs/examples/java/src/main/java/com/taos/example/WsConsumerLoopImp.java b/docs/examples/java/src/main/java/com/taos/example/WsConsumerLoopImp.java
index 70e29503f8..77c6a4fd1b 100644
--- a/docs/examples/java/src/main/java/com/taos/example/WsConsumerLoopImp.java
+++ b/docs/examples/java/src/main/java/com/taos/example/WsConsumerLoopImp.java
@@ -1,7 +1,7 @@
 package com.taos.example;
 
-import com.alibaba.fastjson.JSON;
 import com.taosdata.jdbc.TSDBDriver;
+import com.taosdata.jdbc.utils.JsonUtil;
 
 import java.sql.Connection;
 import java.sql.DriverManager;
@@ -28,7 +28,11 @@ public abstract class WsConsumerLoopImp {
         final AbsConsumerLoop consumerLoop = new AbsConsumerLoop() {
             @Override
             public void process(ResultBean result) {
-                System.out.println("data: " + JSON.toJSONString(result));
+                try{
+                    System.out.println("data: " + JsonUtil.getObjectMapper().writeValueAsString(result));
+                } catch (Exception e) {
+                    throw new RuntimeException(e);
+                }
             }
         };
 
diff --git a/docs/examples/java/src/main/java/com/taos/example/highvolume/DataBaseMonitor.java b/docs/examples/java/src/main/java/com/taos/example/highvolume/DataBaseMonitor.java
index 8678f65231..fa6ebf0858 100644
--- a/docs/examples/java/src/main/java/com/taos/example/highvolume/DataBaseMonitor.java
+++ b/docs/examples/java/src/main/java/com/taos/example/highvolume/DataBaseMonitor.java
@@ -13,6 +13,9 @@ public class DataBaseMonitor {
     public DataBaseMonitor init() throws SQLException {
         if (conn == null) {
             String jdbcURL = System.getenv("TDENGINE_JDBC_URL");
+            if (jdbcURL == null || jdbcURL == ""){
+                jdbcURL = "jdbc:TAOS://localhost:6030?user=root&password=taosdata";
+            }
             conn = DriverManager.getConnection(jdbcURL);
             stmt = conn.createStatement();
         }
diff --git a/docs/examples/java/src/main/java/com/taos/example/highvolume/SQLWriter.java b/docs/examples/java/src/main/java/com/taos/example/highvolume/SQLWriter.java
index dc820f161c..1497992f6b 100644
--- a/docs/examples/java/src/main/java/com/taos/example/highvolume/SQLWriter.java
+++ b/docs/examples/java/src/main/java/com/taos/example/highvolume/SQLWriter.java
@@ -69,6 +69,9 @@ public class SQLWriter {
      */
     private static Connection getConnection() throws SQLException {
         String jdbcURL = System.getenv("TDENGINE_JDBC_URL");
+        if (jdbcURL == null || jdbcURL == ""){
+            jdbcURL = "jdbc:TAOS://localhost:6030?user=root&password=taosdata";
+        }
         return DriverManager.getConnection(jdbcURL);
     }
 
diff --git a/docs/examples/java/src/test/java/com/taos/test/TestAll.java b/docs/examples/java/src/test/java/com/taos/test/TestAll.java
index e014a3b315..a92ddd116c 100644
--- a/docs/examples/java/src/test/java/com/taos/test/TestAll.java
+++ b/docs/examples/java/src/test/java/com/taos/test/TestAll.java
@@ -17,6 +17,37 @@ public class TestAll {
                 stmt.execute("drop database if exists " + dbName);
             }
         }
+        waitTransaction();
+    }
+
+    public void dropTopic(String topicName) throws SQLException {
+        String jdbcUrl = "jdbc:TAOS://localhost:6030?user=root&password=taosdata";
+        try (Connection conn = DriverManager.getConnection(jdbcUrl)) {
+            try (Statement stmt = conn.createStatement()) {
+                stmt.execute("drop topic if exists " + topicName);
+            }
+        }
+        waitTransaction();
+    }
+
+    public void waitTransaction() throws SQLException {
+
+        String jdbcUrl = "jdbc:TAOS://localhost:6030?user=root&password=taosdata";
+        try (Connection conn = DriverManager.getConnection(jdbcUrl)) {
+            try (Statement stmt = conn.createStatement()) {
+                for (int i = 0; i < 10; i++) {
+                    stmt.execute("show transactions");
+                    try (ResultSet resultSet = stmt.getResultSet()) {
+                        if (resultSet.next()) {
+                            int count = resultSet.getInt(1);
+                            if (count == 0) {
+                                break;
+                            }
+                        }
+                    }
+                }
+            }
+        }
     }
 
     public void insertData() throws SQLException {
@@ -104,14 +135,20 @@ public class TestAll {
         SubscribeDemo.main(args);
     }
 
-//    @Test
-//    public void testSubscribeJni() throws SQLException, InterruptedException {
-//        dropDB("power");
-//        ConsumerLoopFull.main(args);
-//    }
-//    @Test
-//    public void testSubscribeWs() throws SQLException, InterruptedException {
-//        dropDB("power");
-//        WsConsumerLoopFull.main(args);
-//    }
+    @Test
+    public void testSubscribeJni() throws SQLException, InterruptedException {
+        dropTopic("topic_meters");
+        dropDB("power");
+        ConsumerLoopFull.main(args);
+        dropTopic("topic_meters");
+        dropDB("power");
+    }
+    @Test
+    public void testSubscribeWs() throws SQLException, InterruptedException {
+        dropTopic("topic_meters");
+        dropDB("power");
+        WsConsumerLoopFull.main(args);
+        dropTopic("topic_meters");
+        dropDB("power");
+    }
 }
diff --git a/docs/zh/14-reference/03-taos-sql/21-node.md b/docs/zh/14-reference/03-taos-sql/21-node.md
index 967cb51127..e3a672790c 100644
--- a/docs/zh/14-reference/03-taos-sql/21-node.md
+++ b/docs/zh/14-reference/03-taos-sql/21-node.md
@@ -27,11 +27,15 @@ SHOW DNODES;
 ## 删除数据节点
 
 ```sql
-DROP DNODE dnode_id
+DROP DNODE dnode_id [force] [unsafe]
 ```
 
 注意删除 dnode 不等于停止相应的进程。实际中推荐先将一个 dnode 删除之后再停止其所对应的进程。
 
+只有在线节点可以被删除。如果要强制删除离线节点，需要执行强制删除操作, 即指定force选项。
+
+当节点上存在单副本，并且节点处于离线，如果要强制删除该节点，需要执行非安全删除，即制定unsafe，并且数据不可再恢复。
+
 ## 修改数据节点配置
 
 ```sql
diff --git a/source/libs/monitor/src/monFramework.c b/source/libs/monitor/src/monFramework.c
index a2d03bbd6a..0dbf6e091a 100644
--- a/source/libs/monitor/src/monFramework.c
+++ b/source/libs/monitor/src/monFramework.c
@@ -183,7 +183,7 @@ void monGenClusterInfoTable(SMonInfo *pMonitor){
     }
 
     if (taosHashRemove(tsMonitor.metrics, metric_names[i], strlen(metric_names[i])) != 0) {
-      uError("failed to remove metric %s", metric_names[i]);
+      uTrace("failed to remove metric %s", metric_names[i]);
     }
   } 
 
@@ -652,7 +652,7 @@ void monGenMnodeRoleTable(SMonInfo *pMonitor){
     }
 
     if (taosHashRemove(tsMonitor.metrics, mnodes_role_gauges[i], strlen(mnodes_role_gauges[i])) != 0) {
-      uError("failed to remove metric %s", mnodes_role_gauges[i]);
+      uTrace("failed to remove metric %s", mnodes_role_gauges[i]);
     }
   }
 
@@ -725,7 +725,7 @@ void monGenVnodeRoleTable(SMonInfo *pMonitor){
     }
 
     if (taosHashRemove(tsMonitor.metrics, vnodes_role_gauges[i], strlen(vnodes_role_gauges[i])) != 0) {
-      uError("failed to remove metric %s", vnodes_role_gauges[i]);
+      uTrace("failed to remove metric %s", vnodes_role_gauges[i]);
     }
   }