From d2cdde3887ccd416b053c905aa453ccc4d8b0353 Mon Sep 17 00:00:00 2001
From: Alex Stephen <alexstephen@google.com>
Date: Mon, 21 Sep 2026 18:01:44 +0000
Subject: [PATCH] Avoid duplicating the full value offsets buffer for
 zero-length array slices in Arrow IPC writer.

---
 cpp/src/arrow/ipc/read_write_test.cc | 47 ++++++++++++++++++++++++++++
 cpp/src/arrow/ipc/writer.cc          | 12 ++++++-
 2 files changed, 58 insertions(+), 1 deletion(-)

diff --git a/cpp/src/arrow/ipc/read_write_test.cc b/cpp/src/arrow/ipc/read_write_test.cc
index 15cf0258b2ee..b177dde7ed82 100644
--- a/cpp/src/arrow/ipc/read_write_test.cc
+++ b/cpp/src/arrow/ipc/read_write_test.cc
@@ -3330,6 +3330,53 @@ TEST(PreBuffering, MixedAccess) {
   ASSERT_EQ(2, stats.num_record_batches);
 }
 
+TEST(TestRecordBatchPayload, ZeroLengthArrayValueOffsets) {
+  auto schema = arrow::schema({field("str", utf8())});
+  const auto options = IpcWriteOptions::Defaults();
+
+  // Zero-length array with null offsets buffer
+  {
+    auto array_data = ArrayData::Make(utf8(), /*length=*/0,
+                                      /*buffers=*/{nullptr, nullptr, nullptr});
+    auto batch =
+        RecordBatch::Make(schema, /*num_rows=*/0, {MakeArray(std::move(array_data))});
+    IpcPayload payload;
+    ASSERT_OK(GetRecordBatchPayload(*batch, options, &payload));
+    ASSERT_EQ(payload.body_buffers.size(), 3);
+    ASSERT_EQ(payload.body_buffers[1], nullptr);
+  }
+
+  // Zero-length array with empty offsets buffer
+  {
+    auto empty_buf = Buffer::FromString("");
+    auto array_data = ArrayData::Make(utf8(), /*length=*/0,
+                                      /*buffers=*/{nullptr, empty_buf, empty_buf});
+    auto batch =
+        RecordBatch::Make(schema, /*num_rows=*/0, {MakeArray(std::move(array_data))});
+    IpcPayload payload;
+    ASSERT_OK(GetRecordBatchPayload(*batch, options, &payload));
+    ASSERT_EQ(payload.body_buffers.size(), 3);
+    ASSERT_NE(payload.body_buffers[1], nullptr);
+    ASSERT_EQ(payload.body_buffers[1]->size(), 0);
+  }
+
+  // Zero-length slice of a non-empty array should not retain the parent offsets
+  {
+    auto full_array = ArrayFromJSON(utf8(), R"(["ab", "cd", "ef"])");
+    ASSERT_GT(full_array->data()->buffers[1]->size(),
+              static_cast<int64_t>(sizeof(int32_t)));
+
+    auto empty_slice = full_array->Slice(3, 0);
+    auto batch = RecordBatch::Make(schema, /*num_rows=*/0, {empty_slice});
+    IpcPayload payload;
+    ASSERT_OK(GetRecordBatchPayload(*batch, options, &payload));
+    ASSERT_EQ(payload.body_buffers.size(), 3);
+    ASSERT_NE(payload.body_buffers[1], nullptr);
+    ASSERT_EQ(payload.body_buffers[1]->size(), sizeof(int32_t));
+    ASSERT_EQ(payload.body_buffers[1]->data_as<int32_t>()[0], 0);
+  }
+}
+
 }  // namespace test
 }  // namespace ipc
 }  // namespace arrow
diff --git a/cpp/src/arrow/ipc/writer.cc b/cpp/src/arrow/ipc/writer.cc
index 09a9aef89752..8b57f7442e43 100644
--- a/cpp/src/arrow/ipc/writer.cc
+++ b/cpp/src/arrow/ipc/writer.cc
@@ -325,7 +325,17 @@ class RecordBatchSerializer {
     using offset_type = typename ArrayType::offset_type;
 
     if (array.length() == 0) {
-      *value_offsets = array.value_offsets();
+      if (array.value_offsets() == nullptr || array.value_offsets()->size() == 0) {
+        *value_offsets = array.value_offsets();
+        return Status::OK();
+      }
+      // An offsets buffer for an array of length N contains N + 1 elements, so a
+      // 0-length slice of a non-empty array only needs a single zero offset. Use a
+      // non-owning view over static zero bytes to avoid both a heap allocation and
+      // retaining the full unsliced parent buffer.
+      static constexpr uint64_t kZeroOffset = 0;
+      *value_offsets = std::make_shared<Buffer>(
+          reinterpret_cast<const uint8_t*>(&kZeroOffset), sizeof(offset_type));
       return Status::OK();
     }