Respect max_parts_to_merge_at_once in TTLPartDropMergeSelector

[kssenii]

Changelog category (leave one):

• Improvement

Changelog entry (a user-readable short description of the changes that goes into CHANGELOG.md):

Respect max_parts_to_merge_at_once in TTL drop part merges.

Documentation entry for user-facing changes

• Documentation is written (mandatory for new features)

[clickhouse-gh]

Workflow [PR], commit [de0519c]

Summary: ❌

job_name	test_name	status	info	comment
Stress test (amd_tsan)		failure
	Logical error: Block structure mismatch in A stream: different number of columns: (STID: 0993-2da1)	FAIL	cidb, issue	ISSUE EXISTS
Stress test (arm_asan, s3)		failure
	Segmentation fault (STID: 2704-3fd4)	FAIL	cidb, issue	ISSUE CREATED
Integration tests (amd_asan, targeted)		error		IGNORED

[Copilot]

Pull request overview

This PR adds support for respecting the max_parts_to_merge_at_once setting in TTL drop part merges, which previously only applied to regular merges but not TTL-based operations.

Changes:

• Modified TTLPartDropMergeSelector to accept and enforce max_parts_to_merge_at_once limit
• Updated merge selection logic to track and respect part count limits alongside existing memory and row constraints
• Added integration test to verify the limit is properly enforced during TTL drop merges

Reviewed changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
src/Storages/MergeTree/Compaction/MergeSelectors/TTLMergeSelector.h	Added max_parts_to_merge_at_once parameter to constructors and border-finding methods
src/Storages/MergeTree/Compaction/MergeSelectors/TTLMergeSelector.cpp	Implemented part count tracking and enforcement in merge range selection logic
src/Storages/MergeTree/Compaction/MergeSelectorApplier.cpp	Passed max_parts_to_merge_at_once setting to TTLPartDropMergeSelector constructor
src/Interpreters/PartLog.cpp	Updated documentation to include TTLDropMerge as a merge reason
tests/integration/test_ttl_replicated/test.py	Added comprehensive test verifying part count limit enforcement in TTL drop merges