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[Doc]--Update documents for support consumer priority level in failover mode #7136

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jiazhai merged 2 commits into from
Jun 4, 2020
Merged

[Doc]--Update documents for support consumer priority level in failover mode #7136

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Update Consumer priority level in failover mode
Huanli-Meng Jun 2, 2020
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Update site2/docs/concepts-messaging.md
Huanli-Meng Jun 3, 2020
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6 changes: 3 additions & 3 deletions site2/docs/concepts-messaging.md
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Expand Up @@ -207,11 +207,11 @@ In the diagram below, only **Consumer A-0** is allowed to consume messages.

### Failover

In *failover* mode, multiple consumers can attach to the same subscription. The consumers will be lexically sorted by the consumer's name and the first consumer will initially be the only one receiving messages. This consumer is called the *master consumer*.
In *failover* mode, multiple consumers can attach to the same subscription. In failover mode, the broker selects the master consumer based on the priority level and the lexicographical sorting of a consumer name. If two consumers have an identical priority level, the broker selects the master consumer based on the lexicographical sorting. If these two consumers have different priority levels, the broker selects the consumer with a higher priority level as the master consumer. The master consumer is initially the only one receiving messages. When the master consumer disconnects, all (non-acknowledged and subsequent) messages are delivered to the next consumer in line.

When the master consumer disconnects, all (non-acked and subsequent) messages will be delivered to the next consumer in line.
For partitioned topics, the broker assigns partitioned topics to the consumer with the highest priority level. If multiple consumers have the highest priority level, the broker evenly assigns topics to consumers with these consumers.

In the diagram below, **Consumer-B-0** is the master consumer while **Consumer-B-1** would be the next in line to receive messages if **Consumer-B-0** disconnected.
In the diagram below, **Consumer-B-0** is the master consumer while **Consumer-B-1** would be the next consumer in line to receive messages if **Consumer-B-0** is disconnected.

![Failover subscriptions](assets/pulsar-failover-subscriptions.png)

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