[GitHub] [arrow] lidavidm commented on a diff in pull request #12812: ARROW-16131 [C++] support saving and retrieving custom metadata in batches for IPC file

[GitBox <gi...@apache.org>]

lidavidm commented on code in PR #12812:
URL: https://github.com/apache/arrow/pull/12812#discussion_r845076985


##########
cpp/src/arrow/ipc/writer.cc:
##########
@@ -263,6 +263,14 @@ class RecordBatchSerializer {
     out_->body_length = offset - buffer_start_offset_;
     DCHECK(bit_util::IsMultipleOf8(out_->body_length));
 
+    // copy given record batch's schema metadata to the serializer for serialization
+    auto const &metadata = batch.schema()->metadata();

Review Comment:
   Maybe we should instead add overloads that also allow explicitly passing in metadata to include with the message. Thoughts @pitrou @westonpace?



##########
cpp/src/arrow/ipc/writer.cc:
##########
@@ -263,6 +263,14 @@ class RecordBatchSerializer {
     out_->body_length = offset - buffer_start_offset_;
     DCHECK(bit_util::IsMultipleOf8(out_->body_length));
 
+    // copy given record batch's schema metadata to the serializer for serialization
+    auto const &metadata = batch.schema()->metadata();

Review Comment:
   ```suggestion
       const auto& metadata = batch.schema()->metadata();
   ```
   for consistency



##########
cpp/src/arrow/ipc/writer.cc:
##########
@@ -263,6 +263,14 @@ class RecordBatchSerializer {
     out_->body_length = offset - buffer_start_offset_;
     DCHECK(bit_util::IsMultipleOf8(out_->body_length));
 
+    // copy given record batch's schema metadata to the serializer for serialization
+    auto const &metadata = batch.schema()->metadata();

Review Comment:
   I'm not sure about this change. If the overall schema has metadata, then won't this copy the schema metadata into every batch, duplicating it over and over?



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