Function ChunkedRead

cpp/src/arrow/filesystem/s3fs_benchmark.cc:230–252

Mimic the Parquet reader, reading the file in small chunks.

/// Mimic the Parquet reader, reading the file in small chunks.
static void ChunkedRead(benchmark::State& st, S3FileSystem* fs, const std::string& path) {
  int64_t total_bytes = 0;
  int total_items = 0;
  for (auto _ : st) {
    std::shared_ptr<io::RandomAccessFile> file;
    std::shared_ptr<Buffer> buf;
    int64_t size = 0;
    ASSERT_OK_AND_ASSIGN(file, fs->OpenInputFile(path));
    ASSERT_OK_AND_ASSIGN(size, file->GetSize());
    total_items += 1;

    int64_t offset = 0;
    while (offset < size) {
      const int64_t read = std::min(size, kChunkSize);
      ASSERT_OK_AND_ASSIGN(buf, file->ReadAt(offset, read));
      total_bytes += buf->size();
      offset += buf->size();
    }
  }
  st.SetBytesProcessed(total_bytes);
  st.SetItemsProcessed(total_items);
  std::cerr << "Read the file " << total_items << " times" << std::endl;
}

/// Read the file in small chunks, but using read coalescing.
static void CoalescedRead(benchmark::State& st, S3FileSystem* fs,