[BugFix] Fix sample scan range index overflow in files schema detection

[wyb]

Why I'm doing:

query_id:00000000-0000-0000-0000-000000000000, fragment_instance:00000000-0000-0000-0000-000000000000
*** Aborted at 1763218936 (unix time) try "date -d @1763218936" if you are using GNU date ***
PC: @     0xff99a2202008 (/usr/lib/aarch64-linux-gnu/libc.so.6+0x82007)
*** SIGABRT (@0x3e800231281) received by PID 2298497 (TID 0xff993e4100c0) from PID 2298497; stack trace: ***
    @     0xff99a22053dc (/usr/lib/aarch64-linux-gnu/libc.so.6+0x853db)
    @          0xe481198 google::(anonymous namespace)::FailureSignalHandler(int, siginfo_t*, void*)
    @     0xff99a36588f8 ([vdso]+0x8f7)
    @     0xff99a2202008 (/usr/lib/aarch64-linux-gnu/libc.so.6+0x82007)
    @     0xff99a21ba83c raise
    @     0xff99a21a7134 abort
    @         0x105ac7cc __gnu_cxx::__verbose_terminate_handler()
    @         0x105aac6c __cxxabiv1::__terminate(void (*)())
    @         0x105aacd0 std::terminate()
    @         0x105aae64 __cxa_throw
    @         0x105ab3a8 operator new(unsigned long)
    @          0x77292b0 std::__cxx11::basic_string, std::allocator >::_M_assign(std::__cxx11::basic_string, std::allocator > const&)
    @          0xb0cbabc starrocks::TBrokerRangeDesc::TBrokerRangeDesc(starrocks::TBrokerRangeDesc const&)
    @          0xa5559b8 starrocks::FileScanner::sample_schema(starrocks::RuntimeState*, starrocks::TBrokerScanRange const&, std::vector >*)
    @          0xaa96680 starrocks::PInternalServiceImplBase::_get_file_schema(google::protobuf::RpcController*, starrocks::PGetFileSchemaRequest const*, starrocks::PGetFileSchemaResult*, google::protobuf::Closure*)
    @          0xac1fce4 starrocks::ThreadPool::dispatch_thread()
    @          0xac1658c starrocks::Thread::supervise_thread(void*)
    @     0xff99a2200398 (/usr/lib/aarch64-linux-gnu/libc.so.6+0x80397)
    @     0xff99a2269e9c (/usr/lib/aarch64-linux-gnu/libc.so.6+0xe9e9b)

What I'm doing:

sample scan range index is overflow when sample file count is smaller than total file count.

Fixes #issue

What type of PR is this:

• BugFix
• Feature
• Enhancement
• Refactor
• UT
• Doc
• Tool

Does this PR entail a change in behavior?

• Yes, this PR will result in a change in behavior.
• No, this PR will not result in a change in behavior.

If yes, please specify the type of change:

• Interface/UI changes: syntax, type conversion, expression evaluation, display information
• Parameter changes: default values, similar parameters but with different default values
• Policy changes: use new policy to replace old one, functionality automatically enabled
• Feature removed
• Miscellaneous: upgrade & downgrade compatibility, etc.

Checklist:

• I have added test cases for my bug fix or my new feature
• This pr needs user documentation (for new or modified features or behaviors)
  • I have added documentation for my new feature or new function
• This is a backport pr

Bugfix cherry-pick branch check:

• I have checked the version labels which the pr will be auto-backported to the target branch
  • 4.0
  • 3.5
  • 3.4
  • 3.3

---

Note

Revamps sample_files to a bounded incremental selection to avoid overflow and correctly handle sample >= total, and updates unit tests with cases where total files are fewer than requested samples.

• Backend:
  • File sampling logic: Reworks FileScanner::sample_files to iterate with an incremental rounded index, ensuring indices stay within [0, total-1], always include the last file, and sample all files when sample_file_count >= total_file_count.
• Tests:
  • FileScannerTest::select_sample_files: Adjusts expectations and adds coverage for cases where total_file_count < sample_file_count (e.g., 1/10, 2/8, 10/100).

^{Written by Cursor Bugbot for commit 8210152. This will update automatically on new commits. Configure here.}

[Copilot]

Pull request overview

This PR fixes an index overflow bug in the file schema detection sampling logic that caused crashes (SIGABRT) when the requested sample file count exceeded the total number of available files.

Key Changes:

• Modified the sampling algorithm to iterate based on total_file_count instead of sample_file_count, preventing index overflow
• Added test cases to verify correct behavior when sample_file_count > total_file_count

Reviewed changes

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

File	Description
be/src/exec/file_scanner/file_scanner.cpp	Changed loop from iterating sample_file_count times to iterating while index is within bounds of total_file_count, fixing the overflow bug
be/test/exec/file_scanner/file_scanner_test.cpp	Added two test cases to verify correct sampling behavior when sample count exceeds total file count

[github-actions]

[Java-Extensions Incremental Coverage Report]

✅ pass : 0 / 0 (0%)

[github-actions]

[FE Incremental Coverage Report]

✅ pass : 0 / 0 (0%)

[github-actions]

[BE Incremental Coverage Report]

✅ pass : 6 / 6 (100.00%)

file detail

	path	covered_line	new_line	coverage	not_covered_line_detail
🔵	be/src/exec/file_scanner/file_scanner.cpp	6	6	100.00%	[]

[alvin-celerdata]

@cursor review

[cursor]

✅ Bugbot reviewed your changes and found no bugs!

---

[github-actions]

@Mergifyio backport branch-3.5

[github-actions]

@Mergifyio backport branch-4.0

[github-actions]

@Mergifyio backport branch-3.4

[mergify]

backport branch-3.5

✅ Backports have been created

• #65912 [BugFix] Fix sample scan range index overflow in files schema detection (backport #65894) has been created for branch branch-3.5

[mergify]

backport branch-4.0

🛑 Command backport branch-4.0 cancelled because of a new backport command with different arguments

[mergify]

backport branch-3.4

✅ Backports have been created

• Backport to branch branch-3.4 not needed, change already in branch branch-3.4

[andyziye]

@mergify backport branch-4.0

[mergify]

backport branch-4.0

✅ Backports have been created

• Backport to branch branch-4.0 not needed, change already in branch branch-4.0