refactor: rename scan.allowIncompatible to scan.unsignedSmallIntSafetyCheck #3238
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…yCheck This change renames `spark.comet.scan.allowIncompatible` to `spark.comet.scan.unsignedSmallIntSafetyCheck` and changes its default to `true` (enabled by default). The key change is that ByteType is removed from the safety check entirely, leaving only ShortType subject to fallback behavior. ## Why ByteType is Safe ByteType columns are always safe for native execution because: 1. **Parquet type mapping**: Spark's ByteType can only originate from signed INT8 in Parquet. There is no unsigned 8-bit Parquet type (UINT_8) that maps to ByteType. 2. **UINT_8 maps to ShortType**: When Parquet files contain unsigned UINT_8 columns, Spark maps them to ShortType (16-bit), not ByteType. This is because UINT_8 values (0-255) exceed the signed byte range (-128 to 127). 3. **Truncation preserves signed values**: When storing signed INT8 in 8 bits, the truncation from any wider representation preserves the correct signed value due to two's complement representation. ## Why ShortType Needs the Safety Check ShortType columns may be problematic because: 1. **Ambiguous origin**: ShortType can come from either signed INT16 (safe) or unsigned UINT_8 (potentially incompatible). 2. **Different reader behavior**: Arrow-based readers like DataFusion respect the unsigned UINT_8 logical type and read data as unsigned, while Spark ignores the logical type and reads as signed. This can produce different results for values 128-255. 3. **No metadata available**: At scan time, Comet cannot determine whether a ShortType column originated from INT16 or UINT_8, so the safety check conservatively falls back to Spark for all ShortType columns. Users who know their data does not contain unsigned UINT_8 columns can disable the safety check with `spark.comet.scan.unsignedSmallIntSafetyCheck=false`. Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>
- Use local `root_op` variable instead of unwrapping `exec_context.root_op` - Replace `is_some()` + `unwrap()` pattern with `if let Some(...)` Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>
Codecov Report✅ All modified and coverable lines are covered by tests. Additional details and impacted files@@ Coverage Diff @@
## main #3238 +/- ##
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+ Coverage 56.12% 60.07% +3.95%
- Complexity 976 1437 +461
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Files 119 172 +53
Lines 11743 15929 +4186
Branches 2251 2631 +380
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+ Hits 6591 9570 +2979
- Misses 4012 5031 +1019
- Partials 1140 1328 +188 ☔ View full report in Codecov by Sentry. 🚀 New features to boost your workflow:
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comphead
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Jan 25, 2026
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Thanks @andygrove it is LGTM
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Summary
spark.comet.scan.allowIncompatibletospark.comet.scan.unsignedSmallIntSafetyCheckfalsetotrue(safety check enabled by default)ByteTypefrom the safety check, leaving onlyShortTypesubject to fallbackWhy ByteType is Safe
ByteTypecolumns are always safe for native execution because:Parquet type mapping: Spark's
ByteTypecan only originate from signedINT8in Parquet. There is no unsigned 8-bit Parquet type (UINT_8) that maps toByteType.UINT_8 maps to ShortType: When Parquet files contain unsigned
UINT_8columns, Spark maps them toShortType(16-bit), notByteType. This is becauseUINT_8values (0-255) exceed the signed byte range (-128 to 127).Truncation preserves signed values: When storing signed
INT8in 8 bits, the truncation from any wider representation preserves the correct signed value due to two's complement representation.Why ShortType Needs the Safety Check
ShortTypecolumns may be problematic because:Ambiguous origin:
ShortTypecan come from either signedINT16(safe) or unsignedUINT_8(potentially incompatible).Different reader behavior: Arrow-based readers like DataFusion respect the unsigned
UINT_8logical type and read data as unsigned, while Spark ignores the logical type and reads as signed. This can produce different results for values 128-255.No metadata available: At scan time, Comet cannot determine whether a
ShortTypecolumn originated fromINT16orUINT_8, so the safety check conservatively falls back to Spark for allShortTypecolumns.Users who know their data does not contain unsigned
UINT_8columns can disable the safety check withspark.comet.scan.unsignedSmallIntSafetyCheck=false.🤖 Generated with Claude Code