lidavidm commented on a change in pull request #11616:
URL: https://github.com/apache/arrow/pull/11616#discussion_r785185319
##########
File path: cpp/src/arrow/ipc/reader.cc
##########
@@ -1088,10 +1163,33 @@ class RecordBatchFileReaderImpl : public
RecordBatchFileReader {
return Status::OK();
}
+ Future<std::shared_ptr<RecordBatch>> ReadRecordBatchAsync(int i) {
+ DCHECK_GE(i, 0);
+ DCHECK_LT(i, num_record_batches());
+
+ auto cached_metadata = cached_metadata_.find(i);
+ if (cached_metadata != cached_metadata_.end()) {
+ return ReadCachedRecordBatch(i, cached_metadata->second);
+ }
+
+ return Status::Invalid(
+ "Asynchronous record batch reading is only supported after a call to "
+ "PreBufferMetadata or PreBufferBatches");
+ }
+
Result<std::shared_ptr<RecordBatch>> ReadRecordBatch(int i) override {
DCHECK_GE(i, 0);
DCHECK_LT(i, num_record_batches());
+ auto cached_metadata = cached_metadata_.find(i);
+ if (cached_metadata != cached_metadata_.end()) {
+ return ReadCachedRecordBatch(i, cached_metadata->second).result();
+ }
+
+ // FIXME: What if they have prebuffered metadata and so the dictionary
read has
+ // started but this batch wasn't prebuffered and so the dictionaries
haven't been
+ // finished getting read yet.
Review comment:
Is this FIXME a worry?
##########
File path: cpp/src/arrow/ipc/reader.cc
##########
@@ -1240,6 +1382,14 @@ class RecordBatchFileReaderImpl : public
RecordBatchFileReader {
return std::move(message);
}
+ Result<std::unique_ptr<Message>> ReadCachedMessageFromBlock(const FileBlock&
block) {
+ ++stats_.num_messages;
+ ARROW_ASSIGN_OR_RAISE(std::shared_ptr<Buffer> metadata,
+ metadata_cache_->Read({block.offset,
block.metadata_length}));
+ std::shared_ptr<Buffer> data;
+ return arrow::ipc::ReadMessageFromCached(std::move(metadata),
std::move(data));
+ }
+
Review comment:
I could go either way but it feels like this would be a little clearer
inlined into its only callsite above
##########
File path: cpp/src/arrow/ipc/reader.cc
##########
@@ -1000,6 +1049,13 @@ static Future<std::shared_ptr<Message>>
ReadMessageFromBlockAsync(
io_context);
}
+static Result<std::unique_ptr<Message>> ReadMessageFromCached(
+ std::shared_ptr<Buffer> cached_metadata, std::shared_ptr<Buffer>
cached_data) {
+ ARROW_ASSIGN_OR_RAISE(auto message,
+ ReadMessage(std::move(cached_metadata),
std::move(cached_data)));
+ return std::move(message);
+}
+
Review comment:
I kind of question having this method over just calling ReadMessage
directly.
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