wanglijie95 opened a new pull request, #21646:
URL: https://github.com/apache/flink/pull/21646

   ## What is the purpose of the change
   In the current 
implementation([FLINK-25035](https://issues.apache.org/jira/browse/FLINK-25035)),
 when the upstream vertex parallelism is much greater than the downstream 
vertex parallelism, it may lead to a large number of channels in the downstream 
tasks(for example, A -> B, all to all edge, max parallelism is 1000. If 
parallelism of A is 1000, parallelism of B is decided to be 1, then the only 
subtask of B will consume 1000 * 1000 subpartitions), resulting in a large 
overhead for processing channels.
   
   In this ticket, we temporarily address this issue by limiting the max number 
of subpartitons consumed by each downstream task. The ultimate solution should 
be to support single channel consume multiple subpartitons.
   
   ## Verifying this change
   UT
   
   ## Does this pull request potentially affect one of the following parts:
   
     - Dependencies (does it add or upgrade a dependency): (**no**)
     - The public API, i.e., is any changed class annotated with 
`@Public(Evolving)`: (**no**)
     - The serializers: (**no**)
     - The runtime per-record code paths (performance sensitive): (**no**)
     - Anything that affects deployment or recovery: JobManager (and its 
components), Checkpointing, Kubernetes/Yarn, ZooKeeper: (**no**)
     - The S3 file system connector: (**no**)
   
   ## Documentation
   
     - Does this pull request introduce a new feature? (**no**)
     - If yes, how is the feature documented? (**not applicable**)
   


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