From c564b0f6eea52d8eae39ad6cccddad02c3b2f1c5 Mon Sep 17 00:00:00 2001
From: HuanliMeng <48120384+Huanli-Meng@users.noreply.github.com>
Date: Wed, 3 Jun 2020 15:58:20 +0800
Subject: [PATCH] [Doc]--add retry letter topic to messaging docs.

This doc update is for the PR: https://github.com/apache/pulsar/pull/6449
---
 site2/docs/concepts-messaging.md | 23 +++++++++++++++++++++++
 1 file changed, 23 insertions(+)

diff --git a/site2/docs/concepts-messaging.md b/site2/docs/concepts-messaging.md
index 919bd34069add..ec012ad0fbbc7 100644
--- a/site2/docs/concepts-messaging.md
+++ b/site2/docs/concepts-messaging.md
@@ -160,6 +160,29 @@ Dead letter topic depends on message re-delivery. Messages are redelivered eithe
 > Note    
 > Currently, dead letter topic is enabled only in the shared subscription mode.
 
+### Retry letter topic
+
+For many online business systems, a message needs to be re-consumed because any exception occurs in the business logic processing. Generally, users hope that they can flexibly configure the delay time for re-consuming the failed messages. In this case, you can configure the producer to send messages to both the business topic and the retry letter topic and you can enable automatic retry on the consumer. When automatic retry is enabled on the consumer, a message is stored in the retry letter topic if the messages fail to be consumed and therefore the consumer can automatically consume failed messages from the retry letter topic after a specified delay time.
+
+By default, automatic retry is disabled. You can set `enableRetry` to `true` to enable automatic retry on the consumer.
+
+This example shows how to consumer messages from a retry letter topic.
+
+```java
+Consumer<byte[]> consumer = pulsarClient.newConsumer(Schema.BYTES)
+                .topic(topic)
+                .subscriptionName("my-subscription")
+                .subscriptionType(SubscriptionType.Shared)
+                .enableRetry(true)
+                .receiverQueueSize(100)
+                .deadLetterPolicy(DeadLetterPolicy.builder()
+                        .maxRedeliverCount(maxRedeliveryCount)
+                        .retryLetterTopic("persistent://my-property/my-ns/my-subscription-custom-Retry")
+                        .build())
+                .subscriptionInitialPosition(SubscriptionInitialPosition.Earliest)
+                .subscribe();
+```
+
 ## Topics
 
 As in other pub-sub systems, topics in Pulsar are named channels for transmitting messages from [producers](reference-terminology.md#producer) to [consumers](reference-terminology.md#consumer). Topic names are URLs that have a well-defined structure: