From 39f0aadeb6d15a9253fe4a4ca6d8a6769ccc91a5 Mon Sep 17 00:00:00 2001
From: Adrian Garcia Badaracco <1755071+adriangb@users.noreply.github.com>
Date: Mon, 29 Dec 2025 18:32:42 -0600
Subject: [PATCH] disable array reader cache for nested fields

---
 parquet/src/arrow/array_reader/builder.rs | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/parquet/src/arrow/array_reader/builder.rs b/parquet/src/arrow/array_reader/builder.rs
index 82c8e77f6393..a1ec04dfd916 100644
--- a/parquet/src/arrow/array_reader/builder.rs
+++ b/parquet/src/arrow/array_reader/builder.rs
@@ -152,7 +152,12 @@ impl<'a> ArrayReaderBuilder<'a> {
                     return Ok(Some(reader));
                 };
 
-                if cache_options.projection_mask.leaf_included(col_idx) {
+                // Skip caching for columns with nullable ancestors (def_level > 0)
+                // because CachedArrayReader doesn't support get_def_levels() yet.
+                // See: https://github.com/apache/arrow-rs/issues/XXXX
+                if cache_options.projection_mask.leaf_included(col_idx)
+                    && field.def_level == 0
+                {
                     Ok(Some(Box::new(CachedArrayReader::new(
                         reader,
                         Arc::clone(cache_options.cache),