feat: Use ClickHouse lightweight deletes

[29antonioac]

feat: Use lightweight deletes in ClickHouse

Summary

Replaces ALTER TABLE ... DELETE WHERE with DELETE FROM ... WHERE (lightweight delete) in the ClickHouse delete_and_insert macro.

Background

Elementary's delete_and_insert macro previously deleted rows in ClickHouse using ALTER TABLE ... DELETE WHERE, which triggers a heavy background mutation. Mutations are resource-intensive — they rewrite entire data parts and can lag behind inserts on large tables, causing contention and slow Elementary runs.

Lightweight deletes (DELETE FROM ... WHERE) became GA in ClickHouse 23.3. They work differently: rows are marked with a bitmask and resolved lazily at merge time, making the delete step significantly faster. Since dbt-clickhouse only supports ClickHouse 25.3+, every supported version has lightweight deletes on by default — no server configuration needed.

Changes

• macros/utils/table_operations/delete_and_insert.sql — ALTER TABLE ... DELETE WHERE → DELETE FROM ... ON CLUSTER ... WHERE.

Testing

• Tested against a ClickHouse instance running Elementary monitoring tables

Summary by CodeRabbit

• Bug Fixes
  • Updated ClickHouse row deletion operations to use standard DELETE FROM statements while preserving existing row-matching behavior.
  • Insert operations remain unchanged.

[github-actions]

👋 @29antonioac
Thank you for raising your pull request.
Please make sure to add tests and document all user-facing changes.
You can do this by editing the docs files in the elementary repository.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro

Run ID: ebb0a841-dcfb-4163-a5a7-d4dbc8724de5

📥 Commits

Reviewing files that changed from the base of the PR and between ccb0de3 and e352b70.

📒 Files selected for processing (1)

• macros/utils/table_operations/delete_and_insert.sql

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📝 Walkthrough

Walkthrough

The ClickHouse implementation now generates DELETE FROM for row deletion instead of ALTER TABLE ... DELETE, while preserving the existing predicates, cluster clause, insert behavior, and return structure.

Changes

ClickHouse delete query generation

Layer / File(s)	Summary
Generate ClickHouse DELETE statement macros/utils/table_operations/delete_and_insert.sql	The macro replaces ALTER TABLE ... DELETE WHERE with DELETE FROM ... WHERE and retains the existing deletion predicates.

Estimated code review effort: 2 (Simple) | ~5 minutes

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly matches the main change: switching ClickHouse deletes to lightweight deletes.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

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