Yukang-Lian opened a new pull request, #61089:
URL: https://github.com/apache/doris/pull/61089
### What problem does this PR solve?
Issue Number: close #xxx
Related PR: #xxx
Problem Summary:
## Summary
In cloud mode, schema change (SC) tasks for multi-tablet tables are
submitted to a thread pool with limited workers. Tablets waiting in the queue
cannot do compaction because their `alter_version` is unset (-1), which causes
rowset
accumulation during long queue waits.
This PR sets `alter_version = V0` (from FE request) on new tablets at task
pre-submit time (before enqueue), so that queued new tablets can perform
cumulative compaction on double-write data (versions > V0) while waiting.
## Changes
**BE only — no FE or meta-service changes.**
- `task_worker_pool.h/cpp`: Add `pre_submit_callback` to `TaskWorkerPool`,
invoked synchronously before task enters the thread pool queue.
- `task_worker_pool.cpp`: Implement `set_alter_version_before_enqueue()` —
sets `alter_version = V0` on both base and new tablets before enqueue. Add
unconditional `alter_version` cleanup in `alter_cloud_tablet_callback()`.
- `agent_server.cpp`: Wire up `set_alter_version_before_enqueue` as
pre_submit_callback for the ALTER worker pool.
## Key Design Points
- **V0** (partition visible version from FE) is set at pre-submit time to
enable compaction during queue wait.
- **V1** (base_max_version) is still determined at SC execution time for
rowset conversion alignment — unchanged behavior.
- SC commit atomically replaces rowsets [2, V1] on the new tablet, so any
compaction results in (V0, V1] during queue time are harmlessly discarded.
- Cleanup order: `alter_version` is reset to -1 before `remove_task_info`
to prevent race with same-signature re-submission.
### Release note
None
### Check List (For Author)
- Test <!-- At least one of them must be included. -->
- [ ] Regression test
- [ ] Unit Test
- [ ] Manual test (add detailed scripts or steps below)
- [ ] No need to test or manual test. Explain why:
- [ ] This is a refactor/code format and no logic has been changed.
- [ ] Previous test can cover this change.
- [ ] No code files have been changed.
- [ ] Other reason <!-- Add your reason? -->
- Behavior changed:
- [ ] No.
- [ ] Yes. <!-- Explain the behavior change -->
- Does this need documentation?
- [ ] No.
- [ ] Yes. <!-- Add document PR link here. eg:
https://github.com/apache/doris-website/pull/1214 -->
### Check List (For Reviewer who merge this PR)
- [ ] Confirm the release note
- [ ] Confirm test cases
- [ ] Confirm document
- [ ] Add branch pick label <!-- Add branch pick label that this PR should
merge into -->
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