[GitHub] [incubator-druid] jihoonson opened a new pull request #8924: Fix the potential race between SplittableInputSource.getNumSplits() and SplittableInputSource.createSplits() in TaskMonitor

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

jihoonson opened a new pull request #8924: Fix the potential race between SplittableInputSource.getNumSplits() and SplittableInputSource.createSplits() in TaskMonitor
URL: https://github.com/apache/incubator-druid/pull/8924
 
 
   ### Description
   
   `SplittableInputSource` has two methods for parallel indexing. `getNumSplits()` returns the exact number of splits to process and `createSplits()` returns a stream of `InputSplit`s. Even though they are pretty tightly related to each other, it's not recommended to cache all splits in memory because it could be big if there are too many input splits. However, if it doesn't cache, the number of splits from `getNumSplits()` and `createSplits()` can be different because some files can be created or deleted between calls.
   
   `getNumSplits()` is currently used for 2 purposes in the parallel indexing task. First is to check that all subtasks of a phase has succeeded and second is to estimate the progress of each phase. This PR is to fix the bug above by changing `getNumSplits()` to `getEstimatedNumSplits()`. `ParallelIndexingPhaseRunner` will use the number of `SubTaskSpec`s that it has iterated and compare it against the number of succeeded subtasks to determine the end of the phase. For the phase progress, it will just use the estimated number of total splits which could be wrong but doesn't that harm.
   
   <hr>
   
   This PR has:
   - [x] been self-reviewed.
      - [ ] using the [concurrency checklist](https://github.com/apache/incubator-druid/blob/master/dev/code-review/concurrency.md) (Remove this item if the PR doesn't have any relation to concurrency.)
   - [x] added documentation for new or modified features or behaviors.
   - [x] added Javadocs for most classes and all non-trivial methods. Linked related entities via Javadoc links.
   - [ ] added or updated version, license, or notice information in [licenses.yaml](https://github.com/apache/incubator-druid/blob/master/licenses.yaml)
   - [ ] added comments explaining the "why" and the intent of the code wherever would not be obvious for an unfamiliar reader.
   - [ ] added unit tests or modified existing tests to cover new code paths.
   - [ ] added integration tests.
   - [ ] been tested in a test Druid cluster.
   

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