Validate TPC-DS Q8

[Matt711]

Description

Workaround for #22317

The issue seems to be that we silently drop rows in multi-rank joins (described more in #22318 (comment)). This is why the sum changes non-deterministically from run-to-run. But the changes in that PR don't seem to be sufficient to validate Q8. Therefore, the change in this PR is a workaround until we figure where else we could be dropping rows.

Checklist

• I am familiar with the Contributing Guidelines.
• New or existing tests cover these changes.
• The documentation is up to date with these changes.

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[Matt711]

/ok to test d5290ac

[coderabbitai]

📝 Walkthrough

Walkthrough

Query 8 refactors ZIP prefix filtering logic to materialize prefix columns explicitly before joining. Instead of slicing ZIP strings inline in join keys, prefixes are computed upfront in intersect_zips and the main query, then used as materialized join columns to enable deterministic execution under the streaming executor.

Changes

ZIP prefix materialization for deterministic joins

Layer / File(s)	Summary
Intersect ZIPs with materialized prefix python/cudf_polars/cudf_polars/experimental/benchmarks/pdsds_queries/q8.py	intersect_zips now joins 5-character target and preferred ZIPs, then derives and materializes a 2-character ca_zip_prefix column as the intersection key.
Main query join using precomputed ZIP prefixes python/cudf_polars/cudf_polars/experimental/benchmarks/pdsds_queries/q8.py	Main query derives s_zip_prefix via with_columns and switches the intersect_zips join from inline slice expressions to explicit prefix column matching (s_zip_prefix ↔ ca_zip_prefix).

Estimated code review effort

🎯 2 (Simple) | ⏱️ ~8 minutes

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title 'Validate TPC-DS Q8' is clear and specific, directly referring to the main change which is addressing validation issues for TPC-DS Query 8, a specific benchmark query mentioned throughout the PR objectives and linked issues.
Linked Issues check	✅ Passed	The code changes address the linked issue #22317 by restructuring the join logic in Q8 to work around the silent row-dropping issue in multi-rank joins, implementing a workaround by materializing ZIP prefixes and using precomputed columns for joins instead of inline slice expressions.
Out of Scope Changes check	✅ Passed	All changes are directly scoped to the Q8 query implementation file, focusing on restructuring the join logic to address the validation issue described in issue #22317 with no unrelated modifications.
Docstring Coverage	✅ Passed	Docstring coverage is 100.00% which is sufficient. The required threshold is 80.00%.
Description check	✅ Passed	The pull request description clearly explains the changes as a workaround for a nondeterministic validation failure in TPC-DS Query 8, referencing specific GitHub issues and the root cause (silently dropped rows in multi-rank joins).

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✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

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[Matt711]

/ok to test 401abca

[TomAugspurger]

Looks fine for now, but maybe remove the "Closes #22317" from your PR description and we can use that as the issue to track work on identifying the root cause?

[Matt711]

/merge

[Matt711]

/ok to test ce0da68

[Matt711]

/ok to test 2c47d30