autumnust commented on code in PR #6327:
URL: https://github.com/apache/iceberg/pull/6327#discussion_r1042526245
##########
orc/src/main/java/org/apache/iceberg/orc/ORCSchemaUtil.java:
##########
@@ -442,4 +445,23 @@ static TypeDescription applyNameMapping(TypeDescription
orcSchema, NameMapping n
public static Map<Integer, String> idToOrcName(Schema schema) {
return TypeUtil.visit(schema, new IdToOrcName());
}
+
+ /**
+ * Returns a {@link Schema} which has constant fields and metadata fields
removed from the
+ * provided schema. This utility can be used to create a "read schema" which
can be passed to the
+ * ORC file reader and hence avoiding deserialization and memory costs
associated with column
+ * values already available through Iceberg metadata.
+ *
+ * <p>NOTE: This method, unlike {@link TypeUtil#selectNot(Schema, Set)},
preserves empty structs
+ * (caused due to a struct having all constant fields) so that Iceberg ORC
readers can later add
+ * constant fields in these structs
Review Comment:
nit: Doesn't have to mention the cause for empty structs as there might be
other scenarios like intentional empty struct as part of schema ?
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