Allow passing reader option through ArrayRecordDataSource

python/array_record_data_source.py

@@ -173,11 +173,12 @@ def get_read_instruction(path: PathLikeOrFileInstruction) -> _ReadInstruction:
   )
 
 
-def _create_reader(filename: epath.PathLike):
+def _create_reader(filename: epath.PathLike, additional_reader_options: str):
   """Returns an ArrayRecordReader for the given filename."""
+  reader_options = f"readahead_buffer_size:0,{additional_reader_options}"
   return array_record_module.ArrayRecordReader(
       filename,
-      options="readahead_buffer_size:0",
+      options=reader_options,
       file_reader_buffer_size=32768,
   )
 
@@ -219,6 +220,7 @@ def __init__(
       paths: Union[
           PathLikeOrFileInstruction, Sequence[PathLikeOrFileInstruction]
       ],
+      reader_options: dict[str, str] | None = None,
   ):
     """Creates a new ArrayRecordDataSource object.
 
@@ -238,6 +240,8 @@ def __init__(
         paths/FileInstructions. When you want to read subsets or have a large
         number of files prefer to pass FileInstructions. This makes the
         initialization faster.
+      reader_options: string of comma-separated options to be passed when
+        creating a reader.
     """
     if isinstance(paths, (str, pathlib.Path, FileInstruction)):
       paths = [paths]
@@ -258,6 +262,12 @@ def __init__(
           "Unsupported path format was used. Path format must be "
           "a Sequence, String, pathlib.Path or FileInstruction."
       )
+    if reader_options is None:
+      self._reader_options_string = ""
+    else:
+      self._reader_options_string = ",".join(
+          [f"{k}:{v}" for k, v in reader_options.items()]
+      )
     self._read_instructions = _get_read_instructions(paths)
     self._paths = [ri.filename for ri in self._read_instructions]
     # We open readers lazily when we need to read from them.
@@ -324,7 +334,7 @@ def _ensure_reader_exists(self, reader_idx: int) -> None:
     if self._readers[reader_idx] is not None:
       return
     filename = self._read_instructions[reader_idx].filename
-    reader = _create_reader(filename)
+    reader = _create_reader(filename, self._reader_options_string)
     _check_group_size(filename, reader)
     self._readers[reader_idx] = reader
 

python/array_record_data_source_test.py

@@ -247,6 +247,22 @@ def test_repr(self):
     ])
     self.assertRegex(repr(ar), r"ArrayRecordDataSource\(hash_of_paths=[\w]+\)")
 
+  @flagsaver.flagsaver(grain_use_fast_array_record_reader=False)
+  def test_additional_reader_options(self):
+    indices_to_read = [3, 0, 5, 9, 2, 1, 4, 7, 8, 6]
+    ar = array_record_data_source.ArrayRecordDataSource(
+        [
+            self.testdata_dir / "digits.array_record-00000-of-00002",
+            self.testdata_dir / "digits.array_record-00001-of-00002",
+        ],
+        {"index_storage_option": "in_memory"},
+    )
+    # We need to read the records to trigger the creation of the readers.
+    _ = [ar[x] for x in indices_to_read]
+    self.assertLen(ar._readers, 2)
+    self.assertIsInstance(ar._readers[0], array_record_module.ArrayRecordReader)
+    self.assertIsInstance(ar._readers[1], array_record_module.ArrayRecordReader)
+
 
 class RunInParallelTest(parameterized.TestCase):