adriangb commented on code in PR #20854:
URL: https://github.com/apache/datafusion/pull/20854#discussion_r2926464080
##########
datafusion/datasource-parquet/src/row_filter.rs:
##########
@@ -519,6 +562,149 @@ fn leaf_indices_for_roots(
.collect()
}
+/// Resolves struct field access to specific Parquet leaf column indices
+///
+/// For every `StructFieldAccess`, finds the leaf columns in the Parquet schema
+/// whose path matches the struct root name + field path. This avoids reading
all
+/// leaves of a struct when only specific fields are needed
+fn resolve_struct_field_leaves(
+ accesses: &[StructFieldAccess],
+ file_schema: &Schema,
+ schema_descr: &SchemaDescriptor,
+) -> Vec<usize> {
+ let mut leaf_indices = Vec::new();
+
+ for access in accesses {
+ let root_name = file_schema.field(access.root_index).name();
+ let prefix = std::iter::once(root_name.as_str())
+ .chain(access.field_path.iter().map(|p| p.as_str()))
+ .collect::<Vec<_>>();
+
+ for leaf_idx in 0..schema_descr.num_columns() {
+ let col = schema_descr.column(leaf_idx);
+ let col_path = col.path().parts();
+
+ // A leaf matches if its path starts with our prefix.
+ // e.g., prefix=["s", "value"] matches leaf path ["s", "value"]
+ // prefix=["s", "outer"] matches ["s", "outer", "inner"]
+
+ // a leaf matches iff its path starts with our prefix
+ // for example: prefix=["s", "value"] matches leaf path ["s",
"value"]
+ // prefix=["s", "outer"] matches ["s", "outer",
"inner"]
+ let leaf_matches_path = col_path.len() >= prefix.len()
+ && col_path.iter().zip(prefix.iter()).all(|(a, b)| a == b);
+
+ if leaf_matches_path {
+ leaf_indices.push(leaf_idx);
+ }
+ }
+ }
+
+ leaf_indices
+}
+
+/// Builds a filter schema that includes only the fields actually accessed by
the
+/// filter expression.
+///
+/// For regular (non-struct) columns, the full field type is used.
+/// For struct columns accessed via `get_field`, a pruned struct type is
created
Review Comment:
Okay interesting. I would have thought that `ProjectionMask::leaves`
returned a flat column, not a nested struct. Thanks for explaining 😄
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