shashank created CAMEL-24942:
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Summary: camel-seda - multipleConsumers=true silently
load-balances instead of broadcasting when the consumer URIs differ in any
other option
Key: CAMEL-24942
URL: https://issues.apache.org/jira/browse/CAMEL-24942
Project: Camel
Issue Type: Bug
Components: camel-seda
Reporter: shashank
With {{multipleConsumers=true}} every consumer should get a copy of each
message. The option doc says "When enabled, this option should be specified on
every consumer endpoint". Pub/sub only works when all subscriber routes use
exactly the same endpoint URI:
* The queue is shared by name: {{SedaComponent.getQueueKey()}} drops the query
string.
* Each distinct URI is a separate {{SedaEndpoint}} with its own consumer set
and multicast processor.
* A consumer thread multicasts a polled message only to the consumers of its
own endpoint ({{SedaConsumer.sendToConsumers}} uses
{{getEndpoint().getConsumers()}} /
{{getEndpoint().getConsumerMulticastProcessor()}}).
As a result, subscribers on different endpoints compete for the messages.
Reproduced against 4.23.0-SNAPSHOT, 10 messages sent to {{seda:news}}:
{noformat}
A: seda:news?multipleConsumers=true B:
seda:news?multipleConsumers=true -> A 10, B 10
A: seda:news?multipleConsumers=true B:
seda:news?multipleConsumers=true&concurrentConsumers=2 -> A 2, B 8
A: seda:news?multipleConsumers=true B:
seda:news?multipleConsumers=true&pollTimeout=500 -> A 7, B 3
{noformat}
There is no error or warning. Adding a harmless option such as
{{concurrentConsumers}} to one subscriber is enough to lose the broadcast.
CAMEL-6451 already rejects consumers that mix {{multipleConsumers=true}} and
{{false}} on one queue, but not this case.
Proposed fix, one of:
# Multicast over the consumers of all endpoints that share the
{{QueueReference}}. The reference already tracks its endpoints
({{QueueReference.hasConsumers()}} iterates them).
# Fail at start-up, like the CAMEL-6451 check in
{{SedaEndpoint.createConsumer}}, when a consumer with
{{multipleConsumers=true}} is added to a queue that already has consumers on a
different endpoint instance. Also document that all subscribers must use the
identical URI.
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