[refactor](be) Replace std::unique_ptr with DorisUniqueBufferPtr in SingleValueDataString

[mrhhsg]

What problem does this PR solve?

Issue Number: close #xxx

Problem Summary: SingleValueDataString uses std::unique_ptr<char[]> with new[] for large string storage, which bypasses the Doris memory tracking allocator. This replaces it with DorisUniqueBufferPtr so that allocations go through Allocator and are properly tracked.

Release note

None

Check List (For Author)

• Test: Unit Test (added SingleValueDataStringTest)
• Behavior changed: No
• Does this need documentation: No

What problem does this PR solve?

Issue Number: close #xxx

Related PR: #xxx

Problem Summary:

Release note

None

Check List (For Author)

• Test

  • 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

• Behavior changed:

  • No.
  • Yes.

• Does this need documentation?

  • No.
  • Yes.

Check List (For Reviewer who merge this PR)

• Confirm the release note
• Confirm test cases
• Confirm document
• Add branch pick label

[hello-stephen]

Thank you for your contribution to Apache Doris.
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Please clearly describe your PR:

1. What problem was fixed (it's best to include specific error reporting information). How it was fixed.
2. Which behaviors were modified. What was the previous behavior, what is it now, why was it modified, and what possible impacts might there be.
3. What features were added. Why was this function added?
4. Which code was refactored and why was this part of the code refactored?
5. Which functions were optimized and what is the difference before and after the optimization?

[mrhhsg]

/review

[mrhhsg]

run buildall

[github-actions]

No issues found in this review. The allocator swap in SingleValueDataString preserves the serialized layout via the added static_assert, keeps ownership semantics local to the aggregate state, and the new unit tests cover small/large string mutation, reset, and serialize/deserialize paths. Residual risk: I did not run BE unit tests in this runner, so this conclusion is based on code inspection only.

[Copilot]

Pull request overview

Refactors BE aggregate min/max string state (SingleValueDataString) to allocate large-string storage via Doris’s tracked allocator (instead of new[]), and adds unit tests to validate the behavior/serialization paths.

Changes:

• Replace std::unique_ptr<char[]> with DorisUniqueBufferPtr<char> for SingleValueDataString::large_data allocations.
• Update reset/allocation sites to use the new buffer type.
• Add a new GTest suite covering small/large strings, reset, comparisons, and write/read round-trips.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.

File	Description
be/src/exprs/aggregate/aggregate_function_min_max.h	Switch large-string storage to allocator-tracked buffer + add a size static_assert.
be/test/exprs/aggregate/aggregate_function_min_max_test.cpp	New unit tests exercising SingleValueDataString behavior for small/large values and serialization.

Comments suppressed due to low confidence (1)

be/src/exprs/aggregate/aggregate_function_min_max.h:364

• Switching large_data from std::unique_ptr<char[]> to DorisUniqueBufferPtr<char> likely increases the size of the pointer member (stateful deleter), which reduces MAX_SMALL_STRING_SIZE and can cause more strings to spill to heap allocations than before. If keeping the previous small-string inline threshold matters for performance, consider an alternative that keeps large_data pointer-sized (e.g. store a raw char* and free via Allocator::free(ptr, capacity) in destructor/move/reset, using the existing capacity field) while still routing allocations through the tracked allocator.

    DorisUniqueBufferPtr<char> large_data;

public:
    static constexpr Int32 AUTOMATIC_STORAGE_SIZE = 64;
    static constexpr Int32 MAX_SMALL_STRING_SIZE =
            AUTOMATIC_STORAGE_SIZE - sizeof(size) - sizeof(capacity) - sizeof(large_data);

---

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[Copilot]

core/custom_allocator.h uses std::map/std::vector/std::unique_ptr but doesn’t include the corresponding STL headers itself; by adding this include here, aggregate_function_min_max.h now relies on transitive includes for those types. Add the missing standard headers (e.g. <map>) before including core/custom_allocator.h (or otherwise ensure the needed STL headers are directly included) to avoid brittle compilation depending on unrelated includes.

[hello-stephen]

BE UT Coverage Report

Increment line coverage 100.00% (3/3) 🎉

Increment coverage report
Complete coverage report

Category	Coverage
Function Coverage	53.04% (20147/37984)
Line Coverage	36.59% (189464/517827)
Region Coverage	32.88% (147229/447793)
Branch Coverage	33.99% (64423/189523)

[hello-stephen]

BE Regression && UT Coverage Report

Increment line coverage 100.00% (3/3) 🎉

Increment coverage report
Complete coverage report

Category	Coverage
Function Coverage	73.51% (27345/37198)
Line Coverage	57.22% (295397/516243)
Region Coverage	54.44% (246015/451925)
Branch Coverage	56.10% (106656/190105)

[github-actions]

PR approved by at least one committer and no changes requested.

[github-actions]

PR approved by anyone and no changes requested.