Fix S3 data loss in BlobDepot

[alexvru]

Changelog entry

Fix S3 data loss in BlobDepot

Changelog category

• Not for changelog (changelog entry is not required)

Description for reviewers

This patch fixes possible data loss during S3 blob depot bootup induced by race between loading index and scanning S3 storage for files.

[ydbot]

Run Extra Tests

Run additional tests for this PR. You can customize:

• Test Size: small, medium, large (default: all)
• Test Targets: any directory path (default: ydb/)
• Sanitizers: ASAN, MSAN, TSAN
• Coredumps: enable for debugging (default: off)
• Additional args: custom ya make arguments

[github-actions]

🟢 2025-12-05 18:01:16 UTC The validation of the Pull Request description is successful.

[github-actions]

⚪ 2025-12-05 18:02:37 UTC Pre-commit check linux-x86_64-relwithdebinfo for a8e654c has started.
⚪ 2025-12-05 18:02:55 UTC Artifacts will be uploaded here
⚪ 2025-12-05 18:05:08 UTC ya make is running...
🟡 2025-12-05 19:40:50 UTC Some tests failed, follow the links below. Going to retry failed tests...

Ya make output | Test bloat

TESTS	PASSED	ERRORS	FAILED	SKIPPED	MUTED?
39899	36956	0	7	2905	31

⚪ 2025-12-05 19:41:04 UTC ya make is running... (failed tests rerun, try 2)
🟢 2025-12-05 19:53:04 UTC Tests successful.

Ya make output | Test bloat | Test bloat

TESTS	PASSED	ERRORS	FAILED	SKIPPED	MUTED?
63 (only retried tests)	51	0	0	0	12

🟢 2025-12-05 19:53:12 UTC Build successful.
🟢 2025-12-05 19:53:32 UTC ydbd size 2.3 GiB changed* by +216 Bytes, which is < 100.0 KiB vs main: OK

ydbd size dash	main: fe2b581	merge: a8e654c	diff	diff %
ydbd size	2 466 152 008 Bytes	2 466 152 224 Bytes	+216 Bytes	+0.000%
ydbd stripped size	524 843 136 Bytes	524 843 264 Bytes	+128 Bytes	+0.000%

^{*please be aware that the difference is based on comparing your commit and the last completed build from the post-commit, check comparation}

[github-actions]

⚪ 2025-12-05 18:02:49 UTC Pre-commit check linux-x86_64-release-asan for a8e654c has started.
⚪ 2025-12-05 18:03:09 UTC Artifacts will be uploaded here
⚪ 2025-12-05 18:05:14 UTC ya make is running...
🟡 2025-12-05 19:14:51 UTC Some tests failed, follow the links below. This fail is not in blocking policy yet

Ya make output | Test bloat

TESTS	PASSED	ERRORS	FAILED	SKIPPED	MUTED?
12170	12089	0	57	15	9

🟢 2025-12-05 19:15:00 UTC Build successful.
🟢 2025-12-05 19:15:25 UTC ydbd size 3.8 GiB changed* by +424 Bytes, which is < 100.0 KiB vs main: OK

ydbd size dash	main: fe2b581	merge: a8e654c	diff	diff %
ydbd size	4 127 809 296 Bytes	4 127 809 720 Bytes	+424 Bytes	+0.000%
ydbd stripped size	1 532 692 760 Bytes	1 532 692 952 Bytes	+192 Bytes	+0.000%

^{*please be aware that the difference is based on comparing your commit and the last completed build from the post-commit, check comparation}

[ydbot]

Backport

To backport this PR, click the button next to the target branch and then click "Run workflow" in the Run Actions UI.

Branch	Run
stable-25-2, stable-25-2-1, stable-25-3, stable-25-3-1
stable-25-3, stable-25-3-1
stable-25-3

[ydbot]

Backport results:

• stable-25-3: PR [Backport stable-25-3] PR #30244: Fix S3 data loss in BlobDepot #30248
• stable-25-3-1: PR [Backport stable-25-3-1] PR #30244: Fix S3 data loss in BlobDepot #30249

workflow run