rgbuilds commented on code in PR #26195:
URL: https://github.com/apache/datafusion/pull/26195#discussion_r4291615186
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datafusion/datasource-parquet/src/file_format.rs:
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@@ -272,32 +272,83 @@ fn clear_metadata(
})
}
-/// Marks every field that is missing from at least one of the `file_count`
-/// files as nullable: reading such a file yields nulls for that column.
-fn mark_partially_present_fields_nullable(
- schema: Schema,
- presence: &HashMap<String, usize>,
- file_count: usize,
-) -> Schema {
- if presence.values().all(|&count| count == file_count) {
+/// Widen fields missing from some of their containing schemas. An absent
parent
+/// produces a null parent, not a null value for each required child, so
children
+/// are compared only across files in which their parent exists.
+fn mark_partially_present_fields_nullable(schema: Schema, sources: &[Schema])
-> Schema {
+ if sources.len() <= 1 {
Review Comment:
Good catch! I restored a safe fast path that returns when the recursive
source field trees are identical, both at the schema root and within unchanged
nested levels. I avoided the old top-level-name shortcut because it would hide
the missing-child case fixed here.
In a fresh optimized rerun, identical-schema inference improved by 2.92% for
32 x 128 and 0.23% for 256 x 1,024 versus the pre-fast-path version. Evolving
nested schemas cannot use the shortcut and retain a small inference cost.
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