[GitHub] [incubator-druid] jihoonson opened a new pull request #8114: Fix race between canHandle() and addSegment() in StorageLocation

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

jihoonson opened a new pull request #8114: Fix race between canHandle() and addSegment() in StorageLocation
URL: https://github.com/apache/incubator-druid/pull/8114
 
 
   ### Description
   
   Historicals can use multiple threads to load segments in parallel from deep storage now (https://github.com/apache/incubator-druid/pull/7088, https://github.com/apache/incubator-druid/pull/4966). This could lead an incorrect computation of remaining space in `StorageLocation`.
   
   The current pattern to use `StorageLocation` is:
   
   ```java
   if (location.canHandle(segment)) {
     // load segment files into the location
     location.addSegment(segment);
   }
   ```
   
   Even though each of `canHandle()` and `addSegment()` is synchronized, they are not atomically executed which could lead a wrong estimation of the available space.
   
   This PR fixes this problem to add a new method, `reserve()`, to `StorageLocation`. `reserve()` basically does what `canHandle()` and `addSegment()` atomically. If some error occurs after `reserve()`, the caller should call `remove(segment)` to release the reserved space.
   
   <hr>
   
   This PR has:
   - [x] been self-reviewed.
   - [x] added unit tests or modified existing tests to cover new code paths.

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