liangyepianzhou commented on code in PR #875:
URL: https://github.com/apache/pulsar-site/pull/875#discussion_r1554556263
##########
docs/tutorials-redeliver-messages.md:
##########
@@ -0,0 +1,236 @@
+---
+Id: tutorials-redeliver-messages
+title: Consume best practice
+sidebar_label: "Consume best practice"
+description: Learn how to consume messages and redeliver unacknowledged
messages in Pulsar.
+---
+
+# Consume Best Practice
+
+## Background Knowledge
+
+### Subscription Types
+
+Pulsar is a distributed message system where messages can be sent to topics by
producers and consumed by consumers.
+Consumers can subscribe to the topics in four ways (subscription types):
+
+* **Exclusive**
+* **Failover**
+* **Shared**
+* **Key-shared**
+
+The messages are consumed in order for a single partition in Exclusive and
Failover modes and out of order for Shared and
+Key-shared mode. The main difference between Exclusive and Failover is that in
Exclusive mode, the consumer is exclusive
+to the entire topic, while in Failover mode, the consumer is exclusive to only
one partition. Failover mode allows backup
+consumer connections that are not consumed. The main difference between Shared
and Key-shared is whether their dispatch
Review Comment:
And there are many selector implementations of the selector for the
key-shared mode.
For the `ConsistentHashingStickyKeyConsumerSelector`, it could be like the
following:
```java
public Consumer select(int hash) {
rwLock.readLock().lock();
try {
if (hashRing.isEmpty()) {
return null;
}
List<Consumer> consumerList;
Map.Entry<Integer, List<Consumer>> ceilingEntry =
hashRing.ceilingEntry(hash);
if (ceilingEntry != null) {
consumerList = ceilingEntry.getValue();
} else {
consumerList = hashRing.firstEntry().getValue();
}
return consumerList.get(hash % consumerList.size());
} finally {
rwLock.readLock().unlock();
}
}
```
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