Use temporary decryption buffers in Parquet SerialiedPageReader

Author: adamreeve

cpp/src/parquet/column_reader.cc

@@ -226,8 +226,7 @@ class SerializedPageReader : public PageReader {
         decompression_buffer_(AllocateBuffer(properties_.memory_pool(), 0)),
         page_ordinal_(0),
         seen_num_values_(0),
-        total_num_values_(total_num_values),
-        decryption_buffer_(AllocateBuffer(properties_.memory_pool(), 0)) {
+        total_num_values_(total_num_values) {
     if (crypto_ctx != nullptr) {
       crypto_ctx_ = *crypto_ctx;
       InitDecryption();
@@ -304,8 +303,6 @@ class SerializedPageReader : public PageReader {
   // updated by only the page ordinal.
   std::string data_page_aad_;
   std::string data_page_header_aad_;
-  // Encryption
-  std::shared_ptr<ResizableBuffer> decryption_buffer_;
 };
 
 void SerializedPageReader::InitDecryption() {
@@ -477,14 +474,12 @@ std::shared_ptr<Page> SerializedPageReader::NextPage() {
 
     // Decrypt it if we need to
     if (data_decryptor_ != nullptr) {
-      PARQUET_THROW_NOT_OK(
-          decryption_buffer_->Resize(data_decryptor_->PlaintextLength(compressed_len),
-                                     /*shrink_to_fit=*/false));
-      compressed_len =
-          data_decryptor_->Decrypt(page_buffer->span_as<uint8_t>(),
-                                   decryption_buffer_->mutable_span_as<uint8_t>());
+      auto decryption_buffer = AllocateBuffer(
+          properties_.memory_pool(), data_decryptor_->PlaintextLength(compressed_len));
+      compressed_len = data_decryptor_->Decrypt(
+          page_buffer->span_as<uint8_t>(), decryption_buffer->mutable_span_as<uint8_t>());
 
-      page_buffer = decryption_buffer_;
+      page_buffer = decryption_buffer;
     }
 
     if (page_type == PageType::DICTIONARY_PAGE) {