diff --git a/cpp/src/arrow/adapters/orc/adapter.cc b/cpp/src/arrow/adapters/orc/adapter.cc
index 98784450b3cce..576bd0dada596 100644
--- a/cpp/src/arrow/adapters/orc/adapter.cc
+++ b/cpp/src/arrow/adapters/orc/adapter.cc
@@ -222,6 +222,11 @@ class ORCFileReader::Impl {
     return Init();
   }
 
+  virtual liborc::Reader* GetRawORCReader() {
+    return reader_.get();
+  }
+
+
   Status Init() {
     int64_t nstripes = reader_->getNumberOfStripes();
     stripes_.resize(static_cast<size_t>(nstripes));
@@ -548,6 +553,10 @@ class ORCFileReader::Impl {
     return NextStripeReader(batch_size, empty_vec);
   }
 
+  liborc::Reader* ORCFileReader::GetRawORCReader() {
+    return impl_->GetRawORCReader();
+  }
+
  private:
   MemoryPool* pool_;
   std::unique_ptr<liborc::Reader> reader_;
@@ -559,6 +568,15 @@ ORCFileReader::ORCFileReader() { impl_.reset(new ORCFileReader::Impl()); }
 
 ORCFileReader::~ORCFileReader() {}
 
+liborc::Reader* ORCFileReader::GetRawORCReader() {
+  return impl_->GetRawORCReader();
+}
+
+Status ORCFileReader::Open(const std::shared_ptr<io::RandomAccessFile>& file,
+                           MemoryPool* pool, std::unique_ptr<ORCFileReader>* reader) {
+  return Open(file, pool).Value(reader);
+}
+
 Result<std::unique_ptr<ORCFileReader>> ORCFileReader::Open(
     const std::shared_ptr<io::RandomAccessFile>& file, MemoryPool* pool) {
 #ifdef ARROW_ORC_NEED_TIME_ZONE_DATABASE_CHECK
diff --git a/cpp/src/arrow/adapters/orc/adapter.h b/cpp/src/arrow/adapters/orc/adapter.h
index 4ffff81f355f1..6adb3be5ec5b3 100644
--- a/cpp/src/arrow/adapters/orc/adapter.h
+++ b/cpp/src/arrow/adapters/orc/adapter.h
@@ -30,6 +30,7 @@
 #include "arrow/type_fwd.h"
 #include "arrow/util/macros.h"
 #include "arrow/util/visibility.h"
+#include "arrow/adapters/orc/adapter_util.h"
 
 namespace arrow {
 namespace adapters {
@@ -53,6 +54,19 @@ class ARROW_EXPORT ORCFileReader {
  public:
   ~ORCFileReader();
 
+  /// \brief Creates a new ORC reader.
+  ///
+  /// \param[in] file the data source
+  /// \param[in] pool a MemoryPool to use for buffer allocations
+  /// \param[out] reader the returned reader object
+  /// \return Status
+  ARROW_DEPRECATED("Deprecated in 6.0.0. Use Result-returning overload instead.")
+  static Status Open(const std::shared_ptr<io::RandomAccessFile>& file, MemoryPool* pool,
+                     std::unique_ptr<ORCFileReader>* reader);
+
+  /// \brief Get ORC reader from inside.
+  liborc::Reader* GetRawORCReader();
+
   /// \brief Creates a new ORC reader
   ///
   /// \param[in] file the data source
diff --git a/cpp/src/arrow/ipc/reader.cc b/cpp/src/arrow/ipc/reader.cc
index d272c78560f82..a34517c660108 100644
--- a/cpp/src/arrow/ipc/reader.cc
+++ b/cpp/src/arrow/ipc/reader.cc
@@ -1369,6 +1369,23 @@ class RecordBatchFileReaderImpl : public RecordBatchFileReader {
     return total;
   }
 
+  Result<int64_t> RecordBatchCountRows(int i) override {
+    DCHECK_GE(i, 0);
+    DCHECK_LT(i, num_record_batches());
+    ARROW_ASSIGN_OR_RAISE(auto outer_message,
+                          ReadMessageFromBlock(GetRecordBatchBlock(i)));
+    auto metadata = outer_message->metadata();
+    const flatbuf::Message* message = nullptr;
+    RETURN_NOT_OK(
+        internal::VerifyMessage(metadata->data(), metadata->size(), &message));
+    auto batch = message->header_as_RecordBatch();
+    if (batch == nullptr) {
+      return Status::IOError(
+          "Header-type of flatbuffer-encoded Message is not RecordBatch.");
+    }
+    return batch->length();
+  }
+
   Status Open(const std::shared_ptr<io::RandomAccessFile>& file, int64_t footer_offset,
               const IpcReadOptions& options) {
     owned_file_ = file;
diff --git a/cpp/src/arrow/ipc/reader.h b/cpp/src/arrow/ipc/reader.h
index 888f59a627771..2e876d65f567f 100644
--- a/cpp/src/arrow/ipc/reader.h
+++ b/cpp/src/arrow/ipc/reader.h
@@ -203,6 +203,8 @@ class ARROW_EXPORT RecordBatchFileReader
   /// \brief Computes the total number of rows in the file.
   virtual Result<int64_t> CountRows() = 0;
 
+  virtual Result<int64_t> RecordBatchCountRows(int i) = 0;
+
   /// \brief Begin loading metadata for the desired batches into memory.
   ///
   /// This method will also begin loading all dictionaries messages into memory.
diff --git a/cpp/src/arrow/util/bit_stream_utils.h b/cpp/src/arrow/util/bit_stream_utils.h
index 811694e43b76c..e5a10e48ecc3e 100644
--- a/cpp/src/arrow/util/bit_stream_utils.h
+++ b/cpp/src/arrow/util/bit_stream_utils.h
@@ -272,6 +272,11 @@ inline void GetValue_(int num_bits, T* v, int max_bytes, const uint8_t* buffer,
 #pragma warning(push)
 #pragma warning(disable : 4800)
 #endif
+  if (ARROW_PREDICT_FALSE(*bit_offset >= 64)) {
+    auto msg = std::string("invalid bit offset: ") + std::to_string(*bit_offset);
+    msg += ", may be malformed num_bits: " + std::to_string(num_bits);
+    throw std::runtime_error(msg);
+  }
   *v = static_cast<T>(bit_util::TrailingBits(*buffered_values, *bit_offset + num_bits) >>
                       *bit_offset);
 #ifdef _MSC_VER
diff --git a/cpp/src/parquet/encoding.cc b/cpp/src/parquet/encoding.cc
index 05221568c8fa0..5b567989adf6b 100644
--- a/cpp/src/parquet/encoding.cc
+++ b/cpp/src/parquet/encoding.cc
@@ -2721,7 +2721,7 @@ class DeltaBitPackDecoder : public DecoderImpl, virtual public TypedDecoder<DTyp
   T min_delta_;
   uint32_t mini_block_idx_;
   std::shared_ptr<ResizableBuffer> delta_bit_widths_;
-  int delta_bit_width_;
+  int delta_bit_width_ = 0;
 
   T last_value_;
 };