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Posted to issues@flink.apache.org by "Tan-JiaLiang (via GitHub)" <gi...@apache.org> on 2024/01/15 10:47:24 UTC
[PR] [FLINK-34089] Verify that the subscribed topics match the assigned topics [flink-connector-kafka]
Tan-JiaLiang opened a new pull request, #77:
URL: https://github.com/apache/flink-connector-kafka/pull/77
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## What is the purpose of the change
When we unsubscribe a topic and still restore from the old state, the job will still read data from the unsubscribed topic. I think we should check if that the subscribed topic partitions match the assigned partitions, and throw an error so the user can handle it.
## Brief change log
- *Verify that the subscribed topics match the assigned topics.*
## Verifying this change
This change is already covered by existing tests, such as
- *org.apache.flink.streaming.connectors.kafka.table.KafkaTableITCase#testChangingSubscribedTopicsBeforeResuming.*
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Re: [PR] [FLINK-34089] Verify that the subscribed topics match the assigned topics [flink-connector-kafka]
Posted by "Tan-JiaLiang (via GitHub)" <gi...@apache.org>.
Tan-JiaLiang commented on PR #77:
URL: https://github.com/apache/flink-connector-kafka/pull/77#issuecomment-1899618447
@MartijnVisser
Suppose there is a flink job that subscribes two topics in a source at the same time, TopicA and TopicB.
* Write some data to both TopicA and TopicB.
* Stop the job with savepoint, the offset of TopicA and TopicB will be saved in savepoint.
* Now I change the subscribe topic list, subscribe only the TopicB, and restore from the last savepoint.
* The Flink job will still consume the TopicA record, which will make user feel confused.
So I think it is better to clearly tell the user that we cannot restore from the savepoint because the subscribe list has been changed.
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Re: [PR] [FLINK-34089] Verify that the subscribed topics match the assigned topics [flink-connector-kafka]
Posted by "MartijnVisser (via GitHub)" <gi...@apache.org>.
MartijnVisser commented on PR #77:
URL: https://github.com/apache/flink-connector-kafka/pull/77#issuecomment-1898677487
> When we unsubscribe a topic and still restore from the old state, the job will still read data from the unsubscribed topic.
Isn't this by design? If we would change this, we would rely on Kafka for failure recovery, which is something that we don't want to do.
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Re: [PR] [FLINK-34089] Verify that the subscribed topics match the assigned topics [flink-connector-kafka]
Posted by "MartijnVisser (via GitHub)" <gi...@apache.org>.
MartijnVisser closed pull request #77: [FLINK-34089] Verify that the subscribed topics match the assigned topics
URL: https://github.com/apache/flink-connector-kafka/pull/77
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Re: [PR] [FLINK-34089] Verify that the subscribed topics match the assigned topics [flink-connector-kafka]
Posted by "Tan-JiaLiang (via GitHub)" <gi...@apache.org>.
Tan-JiaLiang commented on PR #77:
URL: https://github.com/apache/flink-connector-kafka/pull/77#issuecomment-1892967906
@tzulitai Hi gordon, can you take a look when you are free?
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Re: [PR] [FLINK-34089] Verify that the subscribed topics match the assigned topics [flink-connector-kafka]
Posted by "Tan-JiaLiang (via GitHub)" <gi...@apache.org>.
Tan-JiaLiang commented on PR #77:
URL: https://github.com/apache/flink-connector-kafka/pull/77#issuecomment-1900142817
But users need to know that they should not use checkpoint & savepoint to restore when they change the subscription topic list. Should we add a validation to prevent users from making mistakes?
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Re: [PR] [FLINK-34089] Verify that the subscribed topics match the assigned topics [flink-connector-kafka]
Posted by "Tan-JiaLiang (via GitHub)" <gi...@apache.org>.
Tan-JiaLiang commented on PR #77:
URL: https://github.com/apache/flink-connector-kafka/pull/77#issuecomment-1899714802
But now I am thinking more carefully, maybe just removing the topics from state that are not in the current subscription list is a better solution.
@MartijnVisser @tzulitai WDYT?
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Re: [PR] [FLINK-34089] Verify that the subscribed topics match the assigned topics [flink-connector-kafka]
Posted by "MartijnVisser (via GitHub)" <gi...@apache.org>.
MartijnVisser commented on PR #77:
URL: https://github.com/apache/flink-connector-kafka/pull/77#issuecomment-1899948823
> But now I am thinking more carefully, maybe just removing the topics from state that are not in the current subscription list is a better solution.
That's what a user indeed should do at this point. Just removing an input topic has implications on your pipeline, and users shouldn't just do that. If users have a requirement to (dynamically) add or remove Kafka topics, they should use the solution that has been brought forward with https://cwiki.apache.org/confluence/pages/viewpage.action?pageId=217389320
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Re: [PR] [FLINK-34089] Verify that the subscribed topics match the assigned topics [flink-connector-kafka]
Posted by "MartijnVisser (via GitHub)" <gi...@apache.org>.
MartijnVisser commented on PR #77:
URL: https://github.com/apache/flink-connector-kafka/pull/77#issuecomment-1900152500
> But users need to know that they should not use checkpoint & savepoint to restore when they change the subscription topic list.
Users still can, but they have to take into consideration the same thing as if you would delete an operator from their job. That's already documented at https://nightlies.apache.org/flink/flink-docs-master/docs/ops/state/savepoints/#what-happens-if-i-delete-an-operator-that-has-state-from-my-job
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