Storage: Fix data race in DeltaMergeStore::checkSegmentUpdate

[JaySon-Huang]

What problem does this PR solve?

Issue Number: close #10455

Problem Summary:

What is changed and how it works?

Storage: Fix data race in `DeltaMergeStore::checkSegmentUpdate`

And add more debug log for flaky test RowKey.ToNextKeyIntHandle
https://do.pingcap.net/jenkins/blue/organizations/jenkins/pingcap%2Ftiflash%2Frelease-8.5%2Fpull_unit_test/detail/pull_unit_test/259/pipeline

�[0;33mNote: Google Test filter = RowKey.ToNextKeyIntHandle
�[m�[0;32m[==========] �[mRunning 1 test from 1 test case.
�[0;32m[----------] �[mGlobal test environment set-up.
�[0;32m[----------] �[m1 test from RowKey
�[0;32m[ RUN      ] �[mRowKey.ToNextKeyIntHandle
[2025/09/26 00:05:24.222 +08:00] [WARN] [RowKeyRangeFromRegion.cpp:110] ["Meet rowkey which has extra suffix, keyspace=4294967295 table_id=1  end_key=7480000000000000015F72800000000000001400 end_key_extra_suffix=00 "] [thread_id=1]
[2025/09/26 00:05:24.223 +08:00] [WARN] [RowKeyRangeFromRegion.cpp:110] ["Meet rowkey which has extra suffix, keyspace=4294967295 table_id=1  end_key=7480000000000000015F72800000000000001401 end_key_extra_suffix=01 "] [thread_id=1]
[2025/09/26 00:05:24.223 +08:00] [INFO] [gtest_key_range.cpp:199] ["key_end=7480000000000000015F728000000000000014 rand_suffix="] [thread_id=1]
/home/jenkins/agent/workspace/tiflash-build-common/tiflash/dbms/src/Storages/DeltaMerge/tests/gtest_key_range.cpp:209: Failure
Expected equality of these values:
  next.toRowKeyValueRef()
    Which is: 32-byte object <00-E4 10-FF 4A-7F 00-00 19-D8 F9-F7 4A-7F 00-00 08-00 00-00 00-00 00-00 15-00 00-00 00-00 00-00>
  range.getEnd()
    Which is: 32-byte object <00-21 67-12 00-00 00-00 D9-DB F9-F7 4A-7F 00-00 08-00 00-00 00-00 00-00 14-00 00-00 00-00 00-00>
/home/jenkins/agent/workspace/tiflash-build-common/tiflash/dbms/src/Storages/DeltaMerge/tests/gtest_key_range.cpp:210: Failure
Expected equality of these values:
  range.getEnd().toDebugString()
    Which is: "20"
  "21"
�[0;31m[  FAILED  ] �[mRowKey.ToNextKeyIntHandle (1 ms)
�[0;32m[----------] �[m1 test from RowKey (1 ms total)

�[0;32m[----------] �[mGlobal test environment tear-down
�[0;32m[==========] �[m1 test from 1 test case ran. (1 ms total)
�[0;32m[  PASSED  ] �[m0 tests.
�[0;31m[  FAILED  ] �[m1 test, listed below:
�[0;31m[  FAILED  ] �[mRowKey.ToNextKeyIntHandle

 1 FAILED TEST

Check List

Tests

• Unit test
• Integration test
• Manual test (add detailed scripts or steps below)
• No code

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

[JaySon-Huang]

/run-sanitizer-test tsan

[JaySon-Huang]

/test pull-integration-next-gen

[JaySon-Huang]

/test pull-integration-next-gen

[ti-chi-bot]

[APPROVALNOTIFIER] This PR is APPROVED

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

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[ti-chi-bot]

[LGTM Timeline notifier]

Timeline:

• 2025-09-26 07:03:56.63781979 +0000 UTC m=+599446.708313471: ☑️ agreed by Lloyd-Pottiger.
• 2025-09-26 07:21:27.96901633 +0000 UTC m=+600498.039510013: ☑️ agreed by JinheLin.