fetch only requested portion columns

[swalrus1]

Changelog entry

Reduce volume of reads for deduplication on CS

Changelog category

• Performance improvement

Description for reviewers

...

[github-actions]

⚪ 2025-10-16 13:22:29 UTC Pre-commit check linux-x86_64-relwithdebinfo for 2f5707c has started.
⚪ 2025-10-16 13:22:43 UTC Artifacts will be uploaded here
⚪ 2025-10-16 13:26:13 UTC ya make is running...
🟡 2025-10-16 14:48:58 UTC Some tests failed, follow the links below. Going to retry failed tests...

Ya make output | Test bloat

TESTS	PASSED	ERRORS	FAILED	SKIPPED	MUTED?
31267	29870	0	1	1373	23

⚪ 2025-10-16 14:49:08 UTC ya make is running... (failed tests rerun, try 2)
🟢 2025-10-16 15:03:58 UTC Tests successful.

Ya make output | Test bloat | Test bloat

TESTS	PASSED	ERRORS	FAILED	SKIPPED	MUTED?
585 (only retried tests)	565	0	0	0	20

🟢 2025-10-16 15:04:01 UTC Build successful.
🟢 2025-10-16 15:04:17 UTC ydbd size 2.3 GiB changed* by +6.0 KiB, which is < 100.0 KiB vs main: OK

ydbd size dash	main: 0cf099b	merge: 2f5707c	diff	diff %
ydbd size	2 424 209 616 Bytes	2 424 215 776 Bytes	+6.0 KiB	+0.000%
ydbd stripped size	516 072 648 Bytes	516 073 352 Bytes	+704 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]

⚪ 2025-10-16 13:22:46 UTC Pre-commit check linux-x86_64-release-asan for 2f5707c has started.
⚪ 2025-10-16 13:22:59 UTC Artifacts will be uploaded here
⚪ 2025-10-16 13:26:32 UTC ya make is running...
🟡 2025-10-16 15:34:05 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?
15481	14968	0	202	293	18

🟢 2025-10-16 15:34:10 UTC Build successful.
🟢 2025-10-16 15:34:32 UTC ydbd size 3.8 GiB changed* by +4.9 KiB, which is < 100.0 KiB vs main: OK

ydbd size dash	main: b84ab08	merge: 2f5707c	diff	diff %
ydbd size	4 033 345 384 Bytes	4 033 350 400 Bytes	+4.9 KiB	+0.000%
ydbd stripped size	1 498 040 928 Bytes	1 498 041 632 Bytes	+704 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]

🟢 2025-10-16 13:30:30 UTC The validation of the Pull Request description is successful.

[Copilot]

Pull Request Overview

This PR optimizes data fetching in the columnshard component by reducing the volume of reads during deduplication operations. The changes ensure that only the requested columns are fetched and assembled, rather than reading entire portions.

Key Changes

• Modified TAskDataStep to correctly apply column filtering based on the presence of ColumnIds
• Updated TAssembleDataStep to accept and use column IDs for creating filtered schemas
• Integrated TFilteredSnapshotSchema to limit schema operations to only requested columns

Reviewed Changes

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

File	Description
ydb/core/tx/columnshard/data_reader/fetching_steps.h	Fixed conditional logic in TAskDataStep, added column filtering to TAssembleDataStep via TFilteredSnapshotSchema, and updated constructor to accept column IDs
ydb/core/tx/columnshard/data_reader/fetcher.cpp	Updated instantiation of TAssembleDataStep to pass entityIds parameter in both fetching methods

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[Copilot]

Duplicate private: access specifier. The second private: on line 313 is redundant since line 310 already establishes private access. Remove the duplicate specifier.

Suggested change

private:

[Vladilen]

как это вообще работало?)