Fix crash in getTopKMarks when limit is zero#95072
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alexey-milovidov merged 1 commit intomasterfrom Jan 25, 2026
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When `LIMIT -0.` (or any expression that evaluates to 0) is used with `use_skip_indexes_for_top_k = 1`, the `getTopKMarks` functions would call `queue.top()` on an empty priority queue, causing undefined behavior and a segmentation fault. The fix adds an early return when `n == 0` in both `getTopKMarks` overloads, since requesting the top 0 elements should return nothing. Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>
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Workflow [PR], commit [8273bfb] Summary: ❌
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Thanks for the fix! I will adjust my code change for same issue in #93893 |
shankar-iyer
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Jan 25, 2026
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Cherry pick #95072 to 25.12: Fix crash in `getTopKMarks` when limit is zero
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Backport #95072 to 25.12: Fix crash in `getTopKMarks` when limit is zero
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When
LIMIT -0.(or any expression that evaluates to 0) is used withuse_skip_indexes_for_top_k = 1, thegetTopKMarksfunctions would callqueue.top()on an empty priority queue, causing undefined behavior and a segmentation fault.The fix adds an early return when
n == 0in bothgetTopKMarksoverloads, since requesting the top 0 elements should return nothing.Changelog category (leave one):
Changelog entry (a user-readable short description of the changes that goes into CHANGELOG.md):
Fix crash in the top K optimization when
LIMITis zero. Closes #93893.See https://s3.amazonaws.com/clickhouse-test-reports/json.html?PR=95065&sha=e047a3f739277d9272ec5108eb879df601c7aaf7&name_0=PR&name_1=AST%20fuzzer%20%28arm_asan%29
Checked manually that the new test reproduces the issue on the debug build.