Fix Int32 exponent overflow in SAMPLE ratio parser

[Algunenano]

Closes: #103517

ParserSampleRatio read the exponent of a SAMPLE ratio into an Int32 using the pointer-returning tryReadIntText, which discards the overflow result. On overflow the exponent was left at 0 while the position still advanced, so the only check (whether characters were consumed) passed and a huge or tiny exponent silently became 1e0. For example SELECT count() FROM t SAMPLE 1e-3000000000 sampled 100% of the data instead of ~0 rows.

The exponent is now read via a helper that saturates the magnitude through the existing readUInt128Text path, so any exponent magnitude (not just the Int32/Int64 range) is handled correctly.

Changelog category (leave one):

• Bug Fix (user-visible misbehavior in an official stable release)

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

Fix SAMPLE ratios with an exponent whose magnitude overflows Int32 (e.g. SAMPLE 1e-3000000000) being silently treated as SAMPLE 1.

Version info

• Merged into: 26.7.1.591 (included in 26.7 and later)

[clickhouse-gh]

Workflow [PR], commit [a54fce5]

Summary: ✅

• Performance Comparison: Performance dashboard

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AI Review

Summary

This PR fixes ParserSampleRatio so overflowing scientific-notation exponents no longer silently collapse to 1e0, and it now handles _ digit separators consistently across both the mantissa and exponent. The current code matches that contract, the added stateless test covers the original overflow bug plus the grouped-spelling follow-up, and I did not find a remaining correctness or compatibility issue in the live diff.

Missing context / blind spots

• ⚠️ I could not fetch the Praktika CI report with .claude/tools/fetch_ci_report.js because the current GitHub token is rejected by the enterprise policy, so this review does not include an independent pass over any current CI failures.

Final Verdict

✅ No remaining blockers or majors from this review.

[clickhouse-gh]

LLVM Coverage Report

Metric	Baseline	Current	Δ
Lines	85.50%	85.60%	+0.10%
Functions	92.70%	92.70%	+0.00%
Branches	77.70%	77.70%	+0.00%

Changed lines: Changed C/C++ lines covered: 37/38 (97.37%) · Uncovered code

Full report · Diff report