hongzhi-gao opened a new pull request, #18114:
URL: https://github.com/apache/iotdb/pull/18114
## Description
### Problem
During datanode removal, multiple DataRegions may concurrently migrate
snapshots to the same target node. All snapshot staging directories share one
root (`data/datanode/data/snapshot/`). While one region is receiving snapshots,
`getNextFolder()` walks this shared root to compute occupied space; if another
region deletes its staging subdirectory at the same time, `Files.walk` throws
`NoSuchFileException`. This was misinterpreted as "folder full" → node switched
to read-only (`DISK_FULL`) → snapshot transmission failed → region migration /
datanode removal blocked.
### Fix
1. **`JVMCommonUtils.getOccupiedSpace`**: Replace `Files.walk` with
`walkFileTree`; return `CONTINUE` in `visitFileFailed` to ignore entries
deleted during traversal.
2. **`MinFolderOccupiedSpaceFirstStrategy`**: On refresh failure, keep the
previous cached occupied space instead of setting `Long.MAX_VALUE`.
3. **`FolderManager`**: Only switch to read-only when no healthy folder has
available disk space (`hasSpace()`), not merely when folder selection fails.
### Tests
- `JVMCommonUtilsTest.getOccupiedSpaceIgnoresConcurrentlyDeletedEntries`
-
`MinFolderOccupiedSpaceFirstStrategyRealFsTest.getNextFolderDoesNotEnterReadOnlyWhenDiskHasSpace`
<hr>
This PR has:
- [x] been self-reviewed.
- [x] concurrent read
- [ ] concurrent write
- [ ] concurrent read and write
- [ ] added documentation for new or modified features or behaviors.
- [ ] added Javadocs for most classes and all non-trivial methods.
- [ ] added or updated version, __license__, or notice information
- [x] added comments explaining the "why" and the intent of the code
wherever would not be obvious for an unfamiliar reader.
- [x] added unit tests or modified existing tests to cover new code paths,
ensuring the threshold for code coverage.
- [ ] added integration tests.
- [ ] been tested in a test IoTDB cluster.
<hr>
##### Key changed/added classes (or packages if there are too many classes)
in this PR
- `org.apache.iotdb.commons.utils.JVMCommonUtils`
-
`org.apache.iotdb.commons.disk.strategy.MinFolderOccupiedSpaceFirstStrategy`
- `org.apache.iotdb.commons.disk.FolderManager`
- `org.apache.iotdb.commons.i18n.UtilMessages`
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