ENH: Add parameter to download BigQuery results with the BigQuery Sto…

…rage API (pandas-dev#26104)

Adds new `use_bqstorage_api` parameter to `read_gbq`. This can speed up
downloads of large data frames.

doc/source/whatsnew/v0.25.0.rst

@@ -367,6 +367,7 @@ I/O
 - Improved the explanation for the failure when value labels are repeated in Stata dta files and suggested work-arounds (:issue:`25772`)
 - Improved :meth:`pandas.read_stata` and :class:`pandas.io.stata.StataReader` to read incorrectly formatted 118 format files saved by Stata (:issue:`25960`)
 - Fixed bug in loading objects from S3 that contain ``#`` characters in the URL (:issue:`25945`)
+- Adds ``use_bqstorage_api`` parameter to :func:`read_gbq` to speed up downloads of large data frames. This feature requires version 0.10.0 of the ``pandas-gbq`` library as well as the ``google-cloud-bigquery-storage`` and ``fastavro`` libraries. (:issue:`26104`)
 
 Plotting
 ^^^^^^^^

pandas/io/gbq.py

@@ -1,7 +1,5 @@
 """ Google BigQuery support """
 
-import warnings
-
 
 def _try_import():
     # since pandas is a dependency of pandas-gbq
@@ -26,7 +24,7 @@ def _try_import():
 def read_gbq(query, project_id=None, index_col=None, col_order=None,
              reauth=False, auth_local_webserver=False, dialect=None,
              location=None, configuration=None, credentials=None,
-             private_key=None, verbose=None):
+             use_bqstorage_api=None, private_key=None, verbose=None):
     """
     Load data from Google BigQuery.
 
@@ -103,6 +101,21 @@ def read_gbq(query, project_id=None, index_col=None, col_order=None,
         *New in version 0.8.0 of pandas-gbq*.
 
         .. versionadded:: 0.24.0
+    use_bqstorage_api : bool, default False
+        Use the `BigQuery Storage API
+        <https://cloud.google.com/bigquery/docs/reference/storage/>`__ to
+        download query results quickly, but at an increased cost. To use this
+        API, first `enable it in the Cloud Console
+        <https://console.cloud.google.com/apis/library/bigquerystorage.googleapis.com>`__.
+        You must also have the `bigquery.readsessions.create
+        <https://cloud.google.com/bigquery/docs/access-control#roles>`__
+        permission on the project you are billing queries to.
+
+        This feature requires version 0.10.0 or later of the ``pandas-gbq``
+        package. It also requires the ``google-cloud-bigquery-storage`` and
+        ``fastavro`` packages.
+
+        .. versionadded:: 0.25.0
     private_key : str, deprecated
         Deprecated in pandas-gbq version 0.8.0. Use the ``credentials``
         parameter and
@@ -131,22 +144,27 @@ def read_gbq(query, project_id=None, index_col=None, col_order=None,
     """
     pandas_gbq = _try_import()
 
-    if dialect is None:
-        dialect = "legacy"
-        warnings.warn(
-            'The default value for dialect is changing to "standard" in a '
-            'future version of pandas-gbq. Pass in dialect="legacy" to '
-            "disable this warning.",
-            FutureWarning,
-            stacklevel=2,
-        )
+    kwargs = {}
+
+    # START: new kwargs.  Don't populate unless explicitly set.
+    if use_bqstorage_api is not None:
+        kwargs["use_bqstorage_api"] = use_bqstorage_api
+    # END: new kwargs
+
+    # START: deprecated kwargs.  Don't populate unless explicitly set.
+    if verbose is not None:
+        kwargs["verbose"] = verbose
+
+    if private_key is not None:
+        kwargs["private_key"] = private_key
+    # END: deprecated kwargs
 
     return pandas_gbq.read_gbq(
         query, project_id=project_id, index_col=index_col,
         col_order=col_order, reauth=reauth,
         auth_local_webserver=auth_local_webserver, dialect=dialect,
         location=location, configuration=configuration,
-        credentials=credentials, verbose=verbose, private_key=private_key)
+        credentials=credentials, **kwargs)
 
 
 def to_gbq(dataframe, destination_table, project_id=None, chunksize=None,

pandas/tests/io/test_gbq.py

@@ -8,7 +8,6 @@
 
 import pandas as pd
 from pandas import DataFrame
-import pandas.util.testing as tm
 
 api_exceptions = pytest.importorskip("google.api_core.exceptions")
 bigquery = pytest.importorskip("google.cloud.bigquery")
@@ -90,16 +89,59 @@ def make_mixed_dataframe_v2(test_size):
                      index=range(test_size))
 
 
-def test_read_gbq_without_dialect_warns_future_change(monkeypatch):
-    # Default dialect is changing to standard SQL. See:
-    # https://github.com/pydata/pandas-gbq/issues/195
+def test_read_gbq_with_deprecated_kwargs(monkeypatch):
+    captured_kwargs = {}
 
-    def mock_read_gbq(*args, **kwargs):
+    def mock_read_gbq(sql, **kwargs):
+        captured_kwargs.update(kwargs)
         return DataFrame([[1.0]])
 
-    monkeypatch.setattr(pandas_gbq, 'read_gbq', mock_read_gbq)
-    with tm.assert_produces_warning(FutureWarning):
-        pd.read_gbq("SELECT 1")
+    monkeypatch.setattr("pandas_gbq.read_gbq", mock_read_gbq)
+    private_key = object()
+    pd.read_gbq("SELECT 1", verbose=True, private_key=private_key)
+
+    assert captured_kwargs["verbose"]
+    assert captured_kwargs["private_key"] is private_key
+
+
+def test_read_gbq_without_deprecated_kwargs(monkeypatch):
+    captured_kwargs = {}
+
+    def mock_read_gbq(sql, **kwargs):
+        captured_kwargs.update(kwargs)
+        return DataFrame([[1.0]])
+
+    monkeypatch.setattr("pandas_gbq.read_gbq", mock_read_gbq)
+    pd.read_gbq("SELECT 1")
+
+    assert "verbose" not in captured_kwargs
+    assert "private_key" not in captured_kwargs
+
+
+def test_read_gbq_with_new_kwargs(monkeypatch):
+    captured_kwargs = {}
+
+    def mock_read_gbq(sql, **kwargs):
+        captured_kwargs.update(kwargs)
+        return DataFrame([[1.0]])
+
+    monkeypatch.setattr("pandas_gbq.read_gbq", mock_read_gbq)
+    pd.read_gbq("SELECT 1", use_bqstorage_api=True)
+
+    assert captured_kwargs["use_bqstorage_api"]
+
+
+def test_read_gbq_without_new_kwargs(monkeypatch):
+    captured_kwargs = {}
+
+    def mock_read_gbq(sql, **kwargs):
+        captured_kwargs.update(kwargs)
+        return DataFrame([[1.0]])
+
+    monkeypatch.setattr("pandas_gbq.read_gbq", mock_read_gbq)
+    pd.read_gbq("SELECT 1")
+
+    assert "use_bqstorage_api" not in captured_kwargs
 
 
 @pytest.mark.single