[GitHub] [pulsar] BewareMyPower commented on issue #7728: Automatically created topics have no valid schema info

[GitBox <gi...@apache.org>]

BewareMyPower commented on issue #7728:
URL: https://github.com/apache/pulsar/issues/7728#issuecomment-689563807


   The description I've said before is not accurency. If I send a PUT request to create a topic, querying the topic's schema will also returns 404. But a consumer with string schema could still consume it. After that, the topic's schema became string schema.
   
   However, if a topic was created automatically by a consumer without schema, then a consumer with string schema would fail with `Topic does not have schema to check`.
   
   I'm a little confused with
   
   > If these 2 topics don't have any schemas, it is expected to fail with Incompatible schema if you try to subscribe to them using Schema.STRING.
   
   I've read some source code, if the broker only handled admin's create topic request, it would just call `BrokerService.getTopic` and wait until the returned future completed. But if the broker handled client's subscribe command while the topic didn't exist, the broker would do some more, which might lead to the difference behavior.
   
   It looks like a topic without schema has two different states. I'm not familiar with schema, could you give me some help? @sijie 


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