| # BE Core Module — Review Guide |
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| ## Allocator-Aware Containers |
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| Types in `be/src/core/custom_allocator.h` exist to route owned memory through Doris allocation and tracking paths. |
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| ### Checkpoints |
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| - [ ] For BE-owned buffers or containers whose memory should be tracked, prefer `DorisVector`, `DorisMap`, `DorisUniqueBufferPtr`, and related allocator-aware wrappers instead of the corresponding standard library ownership types |
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| ## COW Column Semantics |
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| Vectorized columns (`IColumn`) use intrusive-reference-counted copy-on-write. |
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| ### Checkpoints |
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| - [ ] Exclusive ownership guaranteed before `mutate()` on hot paths? Shared ownership triggers deep copy |
| - [ ] `assume_mutable_ref()` used only when exclusive ownership is already guaranteed? |
| - [ ] After `Block::mutate_columns()`, columns put back with `set_columns()`? |
| - [ ] `convert_to_full_column_if_const()` materializes only `ColumnConst`; ordinary columns may return shared storage? |
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| ## Type System and Serialization |
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| ### Upgrade/Downgrade Compatibility |
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| - [ ] Serialized block/datatype layout changes gated with `be_exec_version` where required? |
| - [ ] Old and new serialization branches updated together (byte-size, serialize, deserialize)? |
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| ### Decimal and Type Metadata |
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| - [ ] Decimal result types check precision growth limits, no accidental incompatible widening? |
| - [ ] `DecimalV2` `original_precision`/`original_scale` set intentionally, not left as `UINT32_MAX` sentinel? |
| - [ ] `TScalarType` optional fields filled for DECIMAL, CHAR/VARCHAR, DATETIMEV2? |
| - [ ] Flattened `TTypeDesc.types` traversal correct for nested complex types? |
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| ## Block Merge Nullable Trap |
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| `MutableBlock::merge_impl()` assumes nullable promotion shape without dynamic checking in release builds. |
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| - [ ] New block merge logic preserves nullable-promotion preconditions? |
