voonhous commented on code in PR #19558:
URL: https://github.com/apache/hudi/pull/19558#discussion_r3755652356


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hudi-client/hudi-spark-client/src/main/scala/org/apache/hudi/SparkFileFormatInternalRowReaderContext.scala:
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@@ -159,7 +159,37 @@ class 
SparkFileFormatInternalRowReaderContext(baseFileReader: SparkColumnarFileR
       structType
     }
 
-    val (readSchema, readFilters) = 
getSchemaAndFiltersForRead(parquetReadStructType, hasRowIndexField)
+    // Internal reads have no catalyst plan, so nothing rewrites VariantType 
fields the way
+    // PushVariantIntoScan does for user queries. Requesting native 
VariantType against a
+    // SHREDDED parquet base file clips the file group to {metadata, value} 
and reads
+    // value=null; write-side callers (compaction, clustering, merge) would 
then persist the
+    // nulls, silently losing the variant data (#19556). Query paths that 
build this context
+    // without sparkRequiredSchema (MOR incremental relation, streaming, CDC) 
hit the same

Review Comment:
   Added the incremental round trip to the compaction test. One precision that 
came out of writing it: on current table versions a batch incremental query 
scans through the file-group-reader file format with a catalyst schema (the 
overlay leg), so that is what the round trip pins. The no-catalyst-schema legs 
-- the streaming source and CDC -- are tracked in #19578, and the impact 
section now says exactly that.
   



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