tonisojandu opened a new pull request, #21294:
URL: https://github.com/apache/pulsar/pull/21294
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Fixes #20635
### Motivation
When broker side schema validation is disabled and consumer receives an Avro
message that has an incompatible schema then sending messages to DLQ fails due
to a client side schema validation. This causes a fast loop that starts
creating producers for DLQ topic, consumer gets stuck and explodes the number
of producer metrics exposed from broker. [Example implementation of this
issue](https://github.com/tonisojandu/pulsar-dlq-schema-issue-example).
### Modifications
By not inferring the DLQ producer schema from the consumer schema and just
producing them as byte schema, this issue is fixed.
### Verifying this change
- [ ] Make sure that the change passes the CI checks.
This change is already mostly covered by existing tests, such as
`org.apache.pulsar.client.impl.ConsumerImplTest`.
However, to cover this specific verification edge case
`org.apache.pulsar.client.impl.ConsumerImpl` would need to refactored to expose
`possibleSendToDeadLetterTopicMessages` for stubbing. Alternatively, a more
complicated component test would be needed that would cover the complete
`ConsumerImpl.messageReceived(CommandMessage cmdMessage, ByteBuf
headersAndPayload, ClientCnx cnx). This would need to deal with encryption and
compression. Did not find an example to base this potential test, so I am not
sure what approach to take here.
Manually checked that the problem was solved in the constructed
[example](https://github.com/tonisojandu/pulsar-dlq-schema-issue-example).
### Does this pull request potentially affect one of the following parts:
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*If the box was checked, please highlight the changes*
- [ ] Dependencies (add or upgrade a dependency)
- [ ] The public API
- [ ] The schema
- [ ] The default values of configurations
- [ ] The threading model
- [ ] The binary protocol
- [ ] The REST endpoints
- [ ] The admin CLI options
- [ ] The metrics
- [ ] Anything that affects deployment
### Documentation
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- [ ] `doc` <!-- Your PR contains doc changes. -->
- [ ] `doc-required` <!-- Your PR changes impact docs and you will update
later -->
- [ ] `doc-not-needed` <!-- Your PR changes do not impact docs -->
- [ ] `doc-complete` <!-- Docs have been already added -->
### Matching PR in forked repository
PR in forked repository: https://github.com/tonisojandu/pulsar
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