fix: Add legacy mode handling to cast Decimal to String#3939
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parthchandra wants to merge 10 commits intoapache:mainfrom
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fix: Add legacy mode handling to cast Decimal to String#3939parthchandra wants to merge 10 commits intoapache:mainfrom
parthchandra wants to merge 10 commits intoapache:mainfrom
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@andygrove @kazuyukitanimura this is ready for review |
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andygrove
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Apr 17, 2026
| let scale_u = scale as usize; | ||
| let num_digits_u = num_digits as usize; | ||
| if scale_u == 0 { | ||
| format!("{sign}{coeff}") |
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not a blocker, but this is doing a new string allocation per row. It could be more efficient to have a re-usable buffer to reduce allocations.
andygrove
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Apr 17, 2026
| val allowNegativeScale = SQLConf.get | ||
| .getConfString("spark.sql.legacy.allowNegativeScaleOfDecimal", "false") | ||
| .toBoolean | ||
| if (allowNegativeScale) Compatible() else Incompatible() |
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Is Comet now compatible across all eval modes?
andygrove
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Apr 17, 2026
| } | ||
| } | ||
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| test("cast TimestampType to StringType - ancient timestamps") { |
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Some of these tests seem unrelated to casting decimal to string
andygrove
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Apr 17, 2026
| // CORRECTED mode writes timestamps as proleptic Gregorian without rebase. | ||
| // Required because generateTimestamps() includes pre-1900 values (e.g. 1900-06-15) | ||
| // which trigger INT96's default EXCEPTION mode when written with certain timezones. | ||
| withSQLConf("spark.sql.parquet.int96RebaseModeInWrite" -> "CORRECTED") { |
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Unrelated to the PR goal, may be better in a separate PR
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Which issue does this PR close?
Part of #286
Fixes: #1068
Rationale for this change
CometCast.canCastToStringhad previously marked DecimalType -> StringType as Compatible with a caveat. However, the native Decimal128 -> String cast was not explicitly handled in cast_array and it was falling through to DataFusion's built-in cast, which was incompatible with Spark legacy mode for large scale values.For example, zero with a large scale: Decimal(38,18) zero exponent = -18 which produced "0E-18" in Spark LEGACY but "0.000000000000000000" from Comet
TRY and ANSI modes are compatible
What changes are included in this PR?
Adds explicit handling for legacy mode
How are these changes tested?
unit tests