From 83426ca330f4f4f2126efbe00603d49abe63011e Mon Sep 17 00:00:00 2001
From: Alexander Rafferty <hello@alexanderrafferty.com>
Date: Sun, 29 Mar 2026 18:14:53 +1100
Subject: [PATCH 1/2] Change occurances of `truncate(0)` to be `clear` instead,
 mostly for `Vec`s but also one `MutableBuffer`.

---
 arrow-buffer/src/buffer/mutable.rs  | 2 +-
 arrow-json/src/reader/value_iter.rs | 2 +-
 parquet/tests/geospatial.rs         | 4 ++--
 3 files changed, 4 insertions(+), 4 deletions(-)

diff --git a/arrow-buffer/src/buffer/mutable.rs b/arrow-buffer/src/buffer/mutable.rs
index 9fc860506194..d64ad3e82009 100644
--- a/arrow-buffer/src/buffer/mutable.rs
+++ b/arrow-buffer/src/buffer/mutable.rs
@@ -1371,7 +1371,7 @@ mod tests {
             assert_eq!(pool.used(), 40);
 
             // Truncate to zero
-            buffer.truncate(0);
+            buffer.clear();
             assert_eq!(buffer.len(), 0);
             assert_eq!(pool.used(), 0);
         }
diff --git a/arrow-json/src/reader/value_iter.rs b/arrow-json/src/reader/value_iter.rs
index f70b893f52a0..ebaba695adf3 100644
--- a/arrow-json/src/reader/value_iter.rs
+++ b/arrow-json/src/reader/value_iter.rs
@@ -73,7 +73,7 @@ impl<R: BufRead> Iterator for ValueIter<R> {
         }
 
         loop {
-            self.line_buf.truncate(0);
+            self.line_buf.clear();
             match self.reader.read_line(&mut self.line_buf) {
                 Ok(0) => {
                     // read_line returns 0 when stream reached EOF
diff --git a/parquet/tests/geospatial.rs b/parquet/tests/geospatial.rs
index 4f449df920e8..fcc93661ed97 100644
--- a/parquet/tests/geospatial.rs
+++ b/parquet/tests/geospatial.rs
@@ -380,8 +380,8 @@ mod test {
 
         for i in 0..reader.num_row_groups() {
             let row_group = reader.get_row_group(i).unwrap();
-            values.truncate(0);
-            def_levels.truncate(0);
+            values.clear();
+            def_levels.clear();
 
             let mut row_group_out = writer.next_row_group().unwrap();
 

From b4c83a9067659bfb5a319747c1a0e7f4ed26cfe2 Mon Sep 17 00:00:00 2001
From: Alexander Rafferty <hello@alexanderrafferty.com>
Date: Sun, 29 Mar 2026 18:15:15 +1100
Subject: [PATCH 2/2] Fixed an inconsistency between `MutableBuffer::truncate`
 and `MutableBuffer::clear`.

---
 arrow-buffer/src/buffer/mutable.rs | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/arrow-buffer/src/buffer/mutable.rs b/arrow-buffer/src/buffer/mutable.rs
index d64ad3e82009..07ef965cb082 100644
--- a/arrow-buffer/src/buffer/mutable.rs
+++ b/arrow-buffer/src/buffer/mutable.rs
@@ -450,7 +450,13 @@ impl MutableBuffer {
 
     /// Clear all existing data from this buffer.
     pub fn clear(&mut self) {
-        self.len = 0
+        self.len = 0;
+        #[cfg(feature = "pool")]
+        {
+            if let Some(reservation) = self.reservation.lock().unwrap().as_mut() {
+                reservation.resize(self.len);
+            }
+        }
     }
 
     /// Returns the data stored in this buffer as a slice.