[jira] [Created] (BEAM-1841) FileBasedSource should better handle when set of files grows while job is running

["Eugene Kirpichov (JIRA)" <ji...@apache.org>]

Eugene Kirpichov created BEAM-1841:
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             Summary: FileBasedSource should better handle when set of files grows while job is running
                 Key: BEAM-1841
                 URL: https://issues.apache.org/jira/browse/BEAM-1841
             Project: Beam
          Issue Type: Bug
          Components: runner-dataflow, sdk-java-core
            Reporter: Eugene Kirpichov
            Assignee: Davor Bonaci


In some cases people run pipelines over directories where the set of files in the directory grows while the job runs. This may lead to a situation like this, in particular with Dataflow runner:

At job submission time, the FileBasedSource estimates the current size of the filepattern, and ends up with a small number. Dataflow runner chooses thus a small desiredBundleSizeBytes to pass to .splitIntoBundles(). However, at the time splitIntoBundles() runs, the set of files has greatly grown, and we produce many more, unnecessarily small bundles, than anticipated.

I see a few things we could do:

- In splitIntoBundles(), compute the actual size and detect when the desired size is unreasonably small for it; e.g. set an upper threshold on how many bundles we produce in total.
- Somehow remember, at submission time, what was the estimated size. Then, in splitIntoBundles(), compute the actual current size, and scale desiredBundleSizeBytes accordingly to get approximately the intended number of bundles. Caveat: files may still change between the moment size is estimated and the moment splitting happens.
- (much larger in scope) Change the whole protocol to use number of bundles instead of bundle size bytes. This probably won't happen with BoundedSource, but it is going to be the case with Splittable DoFn.

Option 1 seems by far the simplest.



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