test: fix flaky DisaggReadSnapshot — skip background tasks during write+mergeDeltaAll

[JaySon-Huang]

What problem does this PR solve?

Issue Number: close #10897

Problem Summary:
DMStoreForSegmentReadTaskTest.DisaggReadSnapshot is flaky — the initial write(4096) schedules a background flush task
whose completion handler (placeDeltaIndex) and follow-up background merge delta both acquire is_updating on
DeltaValueSpace. When mergeDeltaAll() runs before these background tasks release the lock, it fails silently,
leaving 5 persisted column files instead of the expected 4.

What is changed and how it works?

Enable skip_check_segment_update failpoint before the initial write(4096) + mergeDeltaAll() block in the test,
with a scoped guard that disables it on exit. This prevents checkSegmentUpdate from scheduling any background
flush/merge tasks during the setup phase, eliminating the race entirely.

This is consistent with other tests in the same file (fetchPagesNoTinyNoInMem, fetchPagesTinyNoInMem,
fetchPagesTinyInMem) which already enable skip_check_segment_update via disableFlushCache() before their
write+mergeDeltaAll blocks.

Check List

Tests

• Unit test

Side effects

• Performance regression: Consumes more CPU
• Performance regression: Consumes more Memory
• Breaking backward compatibility

Documentation

• Affects user behaviors
• Contains syntax changes
• Contains variable changes
• Contains experimental features
• Changes MySQL compatibility

Release note

None

Summary by CodeRabbit

• Tests
  • Improved reliability of segment snapshot comparison tests by adding explicit control around the stable write/merge sequence used during setup, and ensuring that control is cleaned up afterward. This reduces flaky behavior during snapshot validation and makes test outcomes more consistent.

[pantheon-ai]

@JaySon-Huang I've received your pull request and will start the review. I'll conduct a thorough review covering code quality, potential issues, and implementation details.

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No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Repository UI

Review profile: CHILL

Plan: Pro

Run ID: 7f8e6bdf-7873-4f86-a918-64595d538b85

📥 Commits

Reviewing files that changed from the base of the PR and between fa539e7 and cdd75c2.

📒 Files selected for processing (1)

• dbms/src/Storages/DeltaMerge/tests/gtest_segment_read_task.cpp

🚧 Files skipped from review as they are similar to previous changes (1)

• dbms/src/Storages/DeltaMerge/tests/gtest_segment_read_task.cpp

---

📝 Walkthrough

Walkthrough

The test DisaggReadSnapshot now enables the skip_check_segment_update failpoint before the stable write()/mergeDeltaAll() sequence and disables it via a scope guard afterward to prevent races with background flush during test setup.

Changes

Test Stabilization via Failpoint Control

Layer / File(s)	Summary
Failpoint control for stable write/merge sequence dbms/src/Storages/DeltaMerge/tests/gtest_segment_read_task.cpp	Enable skip_check_segment_update before write()/mergeDeltaAll() and disable it on scope exit via a scope guard, preventing background flush from racing with merge in the stable setup.

Estimated code review effort

🎯 2 (Simple) | ⏱️ ~12 minutes

Poem

A rabbit paused where tests would race,
It set a gentle failpoint in place,
Before the writes and merge took flight,
A scope-guard kept the timing right,
Now tests hop steady through the night 🐰

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Title check	✅ Passed	The PR title clearly and concisely describes the main change: fixing a flaky test by skipping background tasks during write+mergeDeltaAll operations.
Description check	✅ Passed	The PR description follows the repository template, includes issue number (#10897), explains the problem, describes the solution, and completes all required checklist items.
Linked Issues check	✅ Passed	The PR successfully addresses issue #10897 by enabling the skip_check_segment_update failpoint to prevent background tasks from racing with mergeDeltaAll, eliminating the flaky test failure.
Out of Scope Changes check	✅ Passed	All changes in the PR are directly scoped to fixing the flaky test by adding failpoint control; no unrelated modifications are present.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.

_{✏️ Tip: You can configure your own custom pre-merge checks in the settings.}

✨ Finishing Touches

📝 Generate docstrings

• Create stacked PR
• Commit on current branch

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch fix-flaky-test-disagg-read-snapshot

Warning

There were issues while running some tools. Please review the errors and either fix the tool's configuration or disable the tool if it's a critical failure.

🔧 Infer (1.2.0)

dbms/src/Storages/DeltaMerge/tests/gtest_segment_read_task.cpp

dbms/src/Storages/DeltaMerge/tests/gtest_segment_read_task.cpp:15:10: fatal error: 'Common/Logger.h' file not found
15 | #include <Common/Logger.h>
| ^~~~~~~~~~~~~~~~~
1 error generated.
dbms/src/Storages/DeltaMerge/tests/gtest_segment_read_task.cpp:56:5-138:5: ERROR translating statement 'CompoundStmt'
Aborting translation of method 'DB::DM::tests::SegmentReadTaskTest::initInputStream' in file 'dbms/src/Storages/DeltaMerge/tests/gtest_segment_read_task.cpp': "Assert_failure src/clang/cAst_utils.ml:249:53"
Uncaught Internal Error: "Assert_failure src/clang/cAst_utils.ml:249:53"
Error backtrace:
Raised at ClangFrontend__CAst_utils.get_decl_from_typ_ptr in file "src/clang/cAst_utils.ml", line 249, characters 53-65
Called from ClangFrontend__CTrans.CTrans_funct.get_destructor_decl_ref in file "src/clang/cTrans.ml", line 658, characters 12-59
Called from ClangFrontend__CTrans.CTrans_funct.destructor_calls.(fun) in file "src/clang/cTrans.ml", line 2048, characters 12-69
Ca

... [truncated 2200 characters] ...

characters 6-141
Called from ClangFrontend__CFrontend_decl.CFrontend_decl_funct.add_method in file "src/clang/cFrontend_decl.ml" (inlined), line 54, characters 4-52
Called from ClangFrontend__CFrontend_decl.CFrontend_decl_funct.process_method_decl.add_method_if_create_procdesc in file "src/clang/cFrontend_decl.ml" (inlined), line 123, characters 16-158
Called from ClangFrontend__CFrontend_decl.CFrontend_decl_funct.process_method_decl in file "src/clang/cFrontend_decl.ml", line 126, characters 17-97
Called from ClangFrontend__CFrontend_decl.CFrontend_decl_funct.process_methods in file "src/clang/cFrontend_decl.ml" (inlined), line 270, characters 8-122
Called from Stdlib__List.iter in file "list.ml" (inlined), line 110, characters 12-15
Called from Stdlib__List.iter in file "list.ml" (inlin

---

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[JaySon-Huang]

/test pull-integration-test

[ti-chi-bot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: JinheLin, Lloyd-Pottiger

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• OWNERS [JinheLin,Lloyd-Pottiger]

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[ti-chi-bot]

[LGTM Timeline notifier]

Timeline:

• 2026-06-11 05:26:25.683261882 +0000 UTC m=+1024086.753579262: ☑️ agreed by Lloyd-Pottiger.
• 2026-06-11 08:47:20.809940879 +0000 UTC m=+1036141.880258269: ☑️ agreed by JinheLin.

[JaySon-Huang]

/cherry-pick release-nextgen-202603

[ti-chi-bot]

@JaySon-Huang: new pull request created to branch release-nextgen-202603: #10932.

Details

In response to this:

/cherry-pick release-nextgen-202603

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[ti-chi-bot]

In response to a cherrypick label: new pull request created to branch release-8.5: #11035.