Fix NullableT append exception guarantee#535
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slabko
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Pull request overview
This PR fixes exception-safety for ColumnNullableT::Append(...) so that if the nested column’s Append() throws, the nullable column does not end up with an extra (incorrect) null-flag entry. This addresses the inconsistent-size/invalid-access behavior described in PR #376.
Changes:
- Add rollback logic to
ColumnNullableT::Append(...)to erase the last null-flag when nested append throws. - Apply the same rollback behavior to the
ColumnNullableT<ColumnJSON>specialization. - Add a unit test covering the regression case using
ColumnFixedStringthrowing validation errors.
Reviewed changes
Copilot reviewed 3 out of 3 changed files in this pull request and generated 2 comments.
| File | Description |
|---|---|
ut/Column_ut.cpp |
Adds a regression test ensuring nullable size/nulls/nested sizes remain consistent when nested append throws. |
clickhouse/columns/nullable.h |
Adds exception rollback to keep nulls_ consistent if nested append fails. |
clickhouse/columns/json.h |
Mirrors the rollback behavior for the ColumnJSON nullable specialization. |
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Comment on lines
97
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| inline void Append(ValueType value) { | ||
| ColumnNullable::Append(!value.has_value()); | ||
| if (value.has_value()) { | ||
| typed_nested_data_->Append(std::move(*value)); | ||
| } else { | ||
| typed_nested_data_->Append(typename ValueType::value_type{}); | ||
| try { |
| typed_nested_data_->Append(typename ValueType::value_type{}); | ||
| } | ||
| } catch (...) { | ||
| Nulls()->template As<ColumnUInt8>()->Erase(Size() - 1); |
mshustov
approved these changes
Jul 9, 2026
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Fixes #376