diff --git a/pulsar-broker/src/main/java/org/apache/pulsar/broker/service/Consumer.java b/pulsar-broker/src/main/java/org/apache/pulsar/broker/service/Consumer.java
index 275d685280865..176f033a6dcf1 100644
--- a/pulsar-broker/src/main/java/org/apache/pulsar/broker/service/Consumer.java
+++ b/pulsar-broker/src/main/java/org/apache/pulsar/broker/service/Consumer.java
@@ -361,6 +361,12 @@ public Future<Void> sendMessages(final List<? extends Entry> entries, EntryBatch
                 msgOutCounter.add(totalMessages);
                 bytesOutCounter.add(totalBytes);
                 chunkedMessageRate.recordMultipleEvents(totalChunkedMessages, 0);
+            } else {
+                if (log.isDebugEnabled()) {
+                    log.debug("[{}-{}] Sent messages to client fail by IO exception[{}], close the connection"
+                                    + " immediately. Consumer: {}",  topicName, subscription,
+                            status.cause() == null ? "" : status.cause().getMessage(), this.toString());
+                }
             }
         });
         return writeAndFlushPromise;
diff --git a/pulsar-broker/src/main/java/org/apache/pulsar/broker/service/ServerCnx.java b/pulsar-broker/src/main/java/org/apache/pulsar/broker/service/ServerCnx.java
index 194f8593e4aba..651aaf2cba2ea 100644
--- a/pulsar-broker/src/main/java/org/apache/pulsar/broker/service/ServerCnx.java
+++ b/pulsar-broker/src/main/java/org/apache/pulsar/broker/service/ServerCnx.java
@@ -1160,7 +1160,8 @@ protected void handleSubscribe(final CommandSubscribe subscribe) {
                             remoteAddress, getPrincipal());
                 }
 
-                log.info("[{}] Subscribing on topic {} / {}", remoteAddress, topicName, subscriptionName);
+                log.info("[{}] Subscribing on topic {} / {}. consumerId: {}", this.ctx().channel().toString(),
+                        topicName, subscriptionName, consumerId);
                 try {
                     Metadata.validateMetadata(metadata,
                             service.getPulsar().getConfiguration().getMaxConsumerMetadataSize());
@@ -1783,6 +1784,12 @@ protected void handleAck(CommandAck ack) {
                 }
                 return null;
             });
+        } else {
+            if (log.isDebugEnabled()) {
+                log.debug("Consumer future is not complete(not complete or error), but received command ack. so discard"
+                                + " this command. consumerId: {}, cnx: {}, messageIdCount: {}", ack.getConsumerId(),
+                        this.ctx().channel().toString(), ack.getMessageIdsCount());
+            }
         }
     }
 
diff --git a/pulsar-broker/src/test/java/org/apache/pulsar/client/api/SimpleProducerConsumerTest.java b/pulsar-broker/src/test/java/org/apache/pulsar/client/api/SimpleProducerConsumerTest.java
index c45c2b1522f59..0c0e61fe33f88 100644
--- a/pulsar-broker/src/test/java/org/apache/pulsar/client/api/SimpleProducerConsumerTest.java
+++ b/pulsar-broker/src/test/java/org/apache/pulsar/client/api/SimpleProducerConsumerTest.java
@@ -39,6 +39,8 @@
 import com.google.common.collect.Sets;
 import io.netty.buffer.ByteBuf;
 import io.netty.buffer.Unpooled;
+import io.netty.channel.ChannelDuplexHandler;
+import io.netty.channel.ChannelHandlerContext;
 import io.netty.util.Timeout;
 import java.io.ByteArrayInputStream;
 import java.io.IOException;
@@ -84,7 +86,9 @@
 import org.apache.commons.lang3.reflect.FieldUtils;
 import org.apache.commons.lang3.tuple.Pair;
 import org.apache.pulsar.PulsarVersion;
+import org.apache.pulsar.broker.BrokerTestUtil;
 import org.apache.pulsar.broker.PulsarService;
+import org.apache.pulsar.broker.service.ServerCnx;
 import org.apache.pulsar.broker.service.persistent.PersistentTopic;
 import org.apache.pulsar.client.admin.PulsarAdminException;
 import org.apache.pulsar.client.api.schema.GenericRecord;
@@ -4642,4 +4646,50 @@ public void testClientVersion() throws Exception {
         producer2.close();
         client.close();
     }
+
+    @Test
+    public void testConsumeWhenDeliveryFailedByIOException() throws Exception {
+        final String topic = BrokerTestUtil.newUniqueName("persistent://my-property/my-ns/tp_");
+        final String subscriptionName = "subscription1";
+        final int messagesCount = 100;
+        final int receiverQueueSize = 1;
+        Producer<String> producer = pulsarClient.newProducer(Schema.STRING).topic(topic).enableBatching(false).create();
+        ConsumerImpl<String> consumer = (ConsumerImpl<String>) pulsarClient.newConsumer(Schema.STRING).topic(topic)
+                .subscriptionName(subscriptionName).receiverQueueSize(receiverQueueSize).subscribe();
+        for (int i = 0; i < messagesCount; i++) {
+            producer.send(i + "");
+        }
+        // Wait incoming queue of the consumer is full.
+        Awaitility.await().untilAsserted(() -> {
+            assertEquals(consumer.getIncomingMessageSize(), receiverQueueSize);
+        });
+
+        // Mock an io error for sending messages out.
+        ServerCnx serverCnx = (ServerCnx) pulsar.getBrokerService().getTopic(topic, false).join().get()
+                .getSubscription(subscriptionName).getDispatcher().getConsumers().iterator().next().cnx();
+        serverCnx.ctx().channel().pipeline().addFirst(new ChannelDuplexHandler() {
+
+            @Override
+            public void flush(ChannelHandlerContext ctx) throws Exception {
+                throw new IOException("Mocked error");
+            }
+        });
+
+        // Verify all messages will be consumed.
+        Set<String> receivedMessages = new HashSet<>();
+        while (true) {
+            Message<String> msg = consumer.receive(2, TimeUnit.SECONDS);
+            if (msg != null) {
+                receivedMessages.add(msg.getValue());
+                consumer.acknowledge(msg);
+            } else {
+                break;
+            }
+        }
+        Assert.assertEquals(receivedMessages.size(), messagesCount);
+
+        producer.close();
+        consumer.close();
+        admin.topics().delete(topic, false);
+    }
 }