docs: document datetime rebasing and V2 API limitations for DataFusion-based scans#3259
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comphead merged 1 commit intoapache:mainfrom Jan 25, 2026
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…n-based scans Add two new limitations to the shared limitations section for native_datafusion and native_iceberg_compat scan implementations: 1. No support for datetime rebasing detection or the spark.comet.exceptionOnDatetimeRebase configuration. When reading Parquet files with dates/timestamps written before Spark 3.0 (hybrid Julian/Gregorian calendar), these implementations cannot detect legacy values and may produce incorrect results for dates before October 15, 1582. 2. No support for Spark's Datasource V2 API. When V2 is enabled, Comet falls back to native_comet. Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>
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Thanks @andygrove for documenting this
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Summary
native_datafusionandnative_iceberg_compatdo not support datetime rebasing detectionBackground
While investigating
ParquetDatetimeRebaseSuitetests that explicitly setnative_comet, we discovered these are intentional limitations of the DataFusion-based scan implementations, not test issues.Datetime Rebasing
Parquet files written before Spark 3.0 may contain dates/timestamps using the hybrid Julian/Gregorian calendar. The
native_cometimplementation:SparkExceptionwhenspark.comet.exceptionOnDatetimeRebase=trueThe DataFusion-based implementations (
native_datafusion,native_iceberg_compat) do not have this detection capability and read all dates/timestamps as Proleptic Gregorian, which may produce incorrect results for dates before October 15, 1582.Datasource V2 API
The DataFusion-based implementations only support Spark's V1 datasource API. When
spark.sql.sources.useV1SourceListdoes not includeparquet, Comet falls back tonative_comet.Test plan
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