[Data] Clarify that num_rows_per_file isn't strict (ray-project#45529)

The parameter name num_rows_per_file suggests that the resulting files should have exactly the specified number of rows, but that isn't the case. This PR clarifies that the value is more of a hint.

Signed-off-by: Balaji Veeramani <[email protected]>

python/ray/data/dataset.py

@@ -2795,6 +2795,8 @@ def write_parquet(
  arguments for each dataset block.
  num_rows_per_file: The target number of rows to write to each file. If
  ``None``, Ray Data writes a system-chosen number of rows to each file.
+ The specified value is a hint, not a strict limit. Ray Data might write
+ more or fewer rows to each file.
  ray_remote_args: Kwargs passed to :meth:`~ray.remote` in the write tasks.
  concurrency: The maximum number of Ray tasks to run concurrently. Set this
  to control number of tasks to run concurrently. This doesn't change the
@@ -2903,6 +2905,8 @@ def write_json(
  arguments for each dataset block.
  num_rows_per_file: The target number of rows to write to each file. If
  ``None``, Ray Data writes a system-chosen number of rows to each file.
+ The specified value is a hint, not a strict limit. Ray Data might write
+ more or fewer rows to each file.
  ray_remote_args: kwargs passed to :meth:`~ray.remote` in the write tasks.
  concurrency: The maximum number of Ray tasks to run concurrently. Set this
  to control number of tasks to run concurrently. This doesn't change the
@@ -3083,6 +3087,8 @@ def write_csv(
  write arguments for each dataset block.
  num_rows_per_file: The target number of rows to write to each file. If
  ``None``, Ray Data writes a system-chosen number of rows to each file.
+ The specified value is a hint, not a strict limit. Ray Data might write
+ more or fewer rows to each file.
  ray_remote_args: kwargs passed to :meth:`~ray.remote` in the write tasks.
  concurrency: The maximum number of Ray tasks to run concurrently. Set this
  to control number of tasks to run concurrently. This doesn't change the
@@ -3183,6 +3189,8 @@ def write_tfrecords(
  look like.
  num_rows_per_file: The target number of rows to write to each file. If
  ``None``, Ray Data writes a system-chosen number of rows to each file.
+ The specified value is a hint, not a strict limit. Ray Data might write
+ more or fewer rows to each file.
  ray_remote_args: kwargs passed to :meth:`~ray.remote` in the write tasks.
  concurrency: The maximum number of Ray tasks to run concurrently. Set this
  to control number of tasks to run concurrently. This doesn't change the
@@ -3267,6 +3275,8 @@ def write_webdataset(
  implementation to write each dataset block to a custom output path.
  num_rows_per_file: The target number of rows to write to each file. If
  ``None``, Ray Data writes a system-chosen number of rows to each file.
+ The specified value is a hint, not a strict limit. Ray Data might write
+ more or fewer rows to each file.
  ray_remote_args: Kwargs passed to ``ray.remote`` in the write tasks.
  concurrency: The maximum number of Ray tasks to run concurrently. Set this
  to control number of tasks to run concurrently. This doesn't change the
@@ -3354,6 +3364,8 @@ def write_numpy(
  look like.
  num_rows_per_file: The target number of rows to write to each file. If
  ``None``, Ray Data writes a system-chosen number of rows to each file.
+ The specified value is a hint, not a strict limit. Ray Data might write
+ more or fewer rows to each file.
  ray_remote_args: kwargs passed to :meth:`~ray.remote` in the write tasks.
  concurrency: The maximum number of Ray tasks to run concurrently. Set this
  to control number of tasks to run concurrently. This doesn't change the