[FLINK-4133] Reflect streaming file source changes in documentation #2198
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| 1. If the `watchType` is set to `FileProcessingMode.PROCESS_CONTINUOUSLY`, when a file is modified, its contents are re-processed entirely. This can brake the "exactly-once" semantics, as appending data at the end of a file will lead to **all** its contents being re-processed. | ||
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| 2. If the `watchType` is set to `FileProcessingMode#PROCESS_ONCE`, the source scans the path **once** and exits, without waiting for the readers to finish reading. This leads to no more checkpoints after that point, thus providing reduced fault-tolerance guarantees. |
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You are referring to the enum types using a . and a #.
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Item 2: doesn't mean that the files are not read completely, right?
Its just that the checkpointing won't work anymore once the input splits have been send to the readers?
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Why are we not keeping the file-monitoring task alive until the job is cancelled?
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- I will integrate that
- You are right. Files are read completely. The only problem is that upon recovery, the job will restart from the last checkpoint, i.e. the last before the source closes.
- when we process once, there is no explicit cancelation required. We decided to close the source explicitly, rather than wait for an external signal. This is also reasonable for resource utilization.
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@rmetzger I updated the PR. |
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Thank you. I'll merge it. |
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Thanks @rmetzger ! |
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The title says it all.
It documents the continuous file processing semantics recently introduced in the Streaming API.