deardeng opened a new pull request, #60480:
URL: https://github.com/apache/doris/pull/60480
## Proposed changes
### Problem
During cloud tablet decommission, some tablets take unexpectedly long time
(5+ minutes) to migrate because FE keeps waiting for warmup tasks to complete,
even though the tasks have already failed on BE side.
**Root cause**: In `FileCacheBlockDownloader::download_file_cache_block()`,
when early return occurs (e.g., tablet not found, rowset not found, storage
resource error), the `_inflight_tablets` count is not decremented. This causes:
1. `check_download_task()` always returns `done=false` for these tablets
2. FE's `checkInflightWarmUpCacheAsync()` waits until timeout (default 300
seconds)
3. Tablet migration is blocked unnecessarily
**Example log showing the issue**:
```
W download_file_cache_block: tablet_id=1769675033824 rowset_id not found,
rowset_id=020000000010fa85...
```
After this warning, the tablet's inflight count remains in
`_inflight_tablets` map, causing the 5-minute wait before FE times out and
proceeds.
### Solution
1. Extract the inflight count decrement logic into a reusable lambda
`decrease_inflight_count`
2. Call `decrease_inflight_count()` in all early return paths:
- When `get_tablet()` fails
- When `rowset_id` is not found
- When `remote_storage_resource()` fails
3. Refactor `download_done` callback to reuse `decrease_inflight_count`,
eliminating code duplication
4. Use value capture for `decrease_inflight_count` in `download_done` lambda
to ensure lifetime safety if the callback is ever called asynchronously in the
future
5. Add unit tests to verify inflight count is correctly decremented on
failures
## Further comments
This bug also causes a minor memory leak: entries in `_inflight_tablets` map
are never cleaned up when warmup fails, slowly accumulating over time (cleared
on BE restart).
## Checklist(Required)
1. Does it affect the original behavior:
- [ ] Yes
- [x] No
2. Has unit tests been added:
- [x] Yes
- [ ] No
3. Has document been added or modified:
- [ ] Yes
- [x] No
4. Does it need to update dependencies:
- [ ] Yes
- [x] No
5. Is there any sharding changes:
- [ ] Yes
- [x] No
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