[GitHub] [beam] damccorm opened a new issue, #21222: No parallelism when using SDFBoundedSourceReader with Flink

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

damccorm opened a new issue, #21222:
URL: https://github.com/apache/beam/issues/21222

   Background: I am using TFX pipelines with Flink as the runner for Beam (flink session cluster using [flink-on-k8s-operator](https://github.com/GoogleCloudPlatform/flink-on-k8s-operator)). The Flink cluster has 2 taskmanagers with 16 cores each, and parallelism is set to 32. TFX components call `beam.io.ReadFromTFRecord` to load data, passing in a glob file pattern. I have a dataset of TFRecords split across 160 files. When I try to run the component, processing for all 160 files ends up in a single subtask in Flink, i.e. the parallelism is effectively 1. See below images:
   
   !https://i.imgur.com/ppba0AL.png!
   
   !https://i.imgur.com/rSTFATn.png!
   
    
    I have tried all manner of Beam/Flink options and different versions of Beam/Flink but the behaviour remains the same.
   
   Furthermore, the behaviour affects anything that uses `apache_beam.io.iobase.SDFBoundedSourceReader`, e.g. `apache_beam.io.parquetio.ReadFromParquet` also has the same issue. Either I'm missing some obscure setting in my configuration, or this is a bug with the Flink runner.
     
   
   Imported from Jira [BEAM-12915](https://issues.apache.org/jira/browse/BEAM-12915). Original Jira may contain additional context.
   Reported by: roganmorrow.


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