flaky test: StorageDeltaMergeTest.RestoreAfterClearData

Bug Report

Please answer these questions before submitting your issue. Thanks!

1. Minimal reproduce step (Required)

https://do.pingcap.net/jenkins/job/pingcap/job/tiflash/job/pull_unit_test/1/stages/log?nodeId=115

2. What did you expect to see? (Required)

All ut passed

3. What did you see instead (Required)

[2026/09/04 15:25:42.340 +08:00] [DEBUG] [DeltaMergeStore.cpp:180] ["Segment task pop from background task pool, segment=<segment_id=38 epoch=0 range=[31,9223372036854775807)> task=Split"] [source="keyspace=4294967295 table_id=1233"] [thread_id=6]
[2026/09/04 15:25:42.340 +08:00] [DEBUG] [Segment.cpp:2060] ["Split - SplitPhysical - Begin prepare, opt_split_point=(null)"] [source="keyspace=4294967295 table_id=1233 segment_id=1 epoch=6"] [thread_id=7]
[2026/09/04 15:25:42.340 +08:00] [INFO] [DeltaMergeStore_InternalSegment.cpp:138] ["Split - Begin, mode=Auto reason=Background safe_point=0 segment=<segment_id=38 epoch=0 range=[31,9223372036854775807) next_segment_id=0 delta_rows=0 delta_bytes=0 delta_deletes=0 stable_file=[dmf_28(v=0)] stable_rows=31 stable_bytes=1116 stable_cols=5 dmf_rows=31 dmf_bytes=1116 dmf_disk_bytes=612 dmf_packs=1>"] [source="keyspace=4294967295 table_id=1233"] [thread_id=6]
[2026/09/04 15:25:42.340 +08:00] [DEBUG] [Segment.cpp:2637] ["Begin segment getReadInfo <segment_id=1 epoch=6 range=[-9223372036854775808,31)>"] [source=" seg_id=1"] [thread_id=7]
[2026/09/04 15:25:42.340 +08:00] [DEBUG] [Segment.cpp:2060] ["Split - SplitPhysical - Begin prepare, opt_split_point=(null)"] [source="keyspace=4294967295 table_id=1233 segment_id=38 epoch=0"] [thread_id=6]
[2026/09/04 15:25:42.340 +08:00] [DEBUG] [Segment.cpp:2637] ["Begin segment getReadInfo <segment_id=38 epoch=0 range=[31,9223372036854775807)>"] [source=" seg_id=38"] [thread_id=6]
[2026/09/04 15:25:42.340 +08:00] [DEBUG] [Segment.cpp:2664] ["Finish segment getReadInfo, my_delta_index=<placed_rows=0 placed_deletes=0 tree_entries=0 tree_inserts=0 tree_deletes=0> fully_indexed=false read_ranges=[[-9223372036854775808,9223372036854775807)] snap={stable_rows=31 persisted_rows=0 persisted_dels=0 persisted_cfs=0 mem_rows=0 mem_dels=0 mem_cfs=0} <segment_id=38 epoch=0 range=[31,9223372036854775807)>"] [source=" seg_id=38"] [thread_id=6]
/home/jenkins/agent/workspace/pingcap/tiflash/pull_unit_test/tiflash/dbms/src/Storages/DeltaMerge/tests/gtest_dm_storage_delta_merge.cpp:885: Failure
Expected equality of these values:
  storage->getStore()->getSegmentsStats().size()
    Which is: 2
  1
[2026/09/04 15:25:42.340 +08:00] [DEBUG] [StableValueSpace.cpp:474] ["StableVS getInputStream start_ts=18446744073709551615 enable_handle_clean_read=false is_fast_mode=false enable_del_clean_read=false"] [source="keyspace=4294967295 table_id=1233 segment_id=38 epoch=0"] [thread_id=6]
[2026/09/04 15:25:42.340 +08:00] [ERROR] [Exception.cpp:93] ["std::exception. Code: 1001, type: testing::AssertionException, e.what() = /home/jenkins/agent/workspace/pingcap/tiflash/pull_unit_test/tiflash/dbms/src/Storages/DeltaMerge/tests/gtest_dm_storage_delta_merge.cpp:885: Failure\nExpected equality of these values:\n  storage->getStore()->getSegmentsStats().size()\n    Which is: 2\n  1"] [source="virtual void DB::DM::tests::StorageDeltaMergeTest_RestoreAfterClearData_Test::TestBody()"] [thread_id=1]
/home/jenkins/agent/workspace/pingcap/tiflash/pull_unit_test/tiflash/dbms/src/Storages/DeltaMerge/tests/gtest_dm_storage_delta_merge.cpp:892: Failure
Failed

4. What is your TiFlash version? (Required)

https://github.com/pingcap/tiflash/pull/11061/changes/6a2ba91e09f7cf20f5958275a30488c46707d7bb from https://github.com/pingcap/tiflash/pull/11061

Start in tiflash/dbms/src/Storages/DeltaMerge/tests/gtest_dm_storage_delta_merge.cpp at lines 885 and 892, focusing on StorageDeltaMergeTest.RestoreAfterClearData. Run this unit test and inspect the logged segment split and restore behavior around the failing segment-count assertions. Done means the test no longer flakes and its expected segment count passes consistently.