russell@unturf.com
76ffba4a60
tidb-0001: partition drop name lookup O(P×D) → O(P+D) (27x at P=8192) tidb-0002: predicate simplification (merged into tidb-0002 in prior commit) tidb-0003: list partition group intersect O(G²) → O(G) (renumbered from 0002) scylladb-0001: UNDF stamp added
20 lines
939 B
Diff
20 lines
939 B
Diff
# UNDF: UNDF-2026-000000529
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# UNDF: (leave blank)
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--- a/cql3/selection/selection.cc
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+++ b/cql3/selection/selection.cc
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@@ -499,11 +499,15 @@ selection::from_selectors(data_dictionary::database db, schema_ptr schema, const
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std::vector<const column_definition*> defs;
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+ // Use an unordered_set for O(1) deduplication instead of O(D) linear
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+ // std::find scan per column reference. For a SELECT with S column
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+ // references over D distinct columns the old code was O(S×D); the patch
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+ // makes it O(S).
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+ std::unordered_set<const column_definition*> defs_seen;
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for (auto&& [sel, alias] : prepared_selectors) {
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expr::for_each_expression<expr::column_value>(sel, [&] (const expr::column_value& cv) {
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- if (std::find(defs.begin(), defs.end(), cv.col) == defs.end()) {
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+ if (defs_seen.insert(cv.col).second) {
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defs.push_back(cv.col);
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}
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});
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}
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