[GitHub] [pulsar] sijie commented on issue #4857: Error: "Trying to subscribe with incompatible schema" even though isSchemaValidationEnforced=false

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sijie commented on issue #4857: Error: "Trying to subscribe with incompatible schema" even though isSchemaValidationEnforced=false 
URL: https://github.com/apache/pulsar/issues/4857#issuecomment-517065570
 
 
   @devinbost 
   
   I think `isSchemaValidationEnforced` is only applied for producers without schema connecting to a topic with schema. We introduced this setting to allow non-java clients (without schema support) still being able to produce messages to the topic.
   
   The error you described is a subscription error. It means a consumer with schema attempts to consume messages from a topic without schema.
   
   In your case,
   
   - the Kafka source is transferring bytes from a Kafka topic to a Pulsar topic. It will create a pulsar topic `persistent://example-tenant/ingest/example-kafka-topic` without schema.
   - The function is consuming from the Pulsar topic `persistent://example-tenant/ingest/example-kafka-topic` with a string schema. (because the schema is inferred from the function input type).
   
   Hence the function will fail to start because the function attempts to consume `persistent://example-tenant/ingest/example-kafka-topic` with a string schema.
   
   ---
   
   There are a few workarounds:
   
   1) you can precreate the topic with `String` schema. so that Kafka source is able to produce with `isSchemaValidationEnforced` setting to true.
   
   2) you can disable schema compatibility check by setting the namespace's schema compatibility check policy to `None`: `bin/pulsar-admin namespaces set-schema-autoupdate-strategy -d tenant/namespace`.
   
   ---
   
   We can also consider extending `isSchemaValidationEnforced` for disabling schema validation completely.

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