googleapis · ashleyxuu · Nov 29, 2023 · Nov 21, 2023 · Nov 21, 2023 · Nov 23, 2023
@@ -486,6 +486,7 @@ def read_gbq(
     index_col: Iterable[str] | str = (),
     col_order: Iterable[str] = (),
     max_results: Optional[int] = None,
+    use_cache: bool = True,
 ) -> bigframes.dataframe.DataFrame:
     _set_default_session_location_if_possible(query_or_table)
     return global_session.with_default_session(
@@ -494,6 +495,7 @@ def read_gbq(
         index_col=index_col,
         col_order=col_order,
         max_results=max_results,
+        use_cache=use_cache,
     )
 
 
@@ -516,6 +518,7 @@ def read_gbq_query(
     index_col: Iterable[str] | str = (),
     col_order: Iterable[str] = (),
     max_results: Optional[int] = None,
+    use_cache: bool = True,
 ) -> bigframes.dataframe.DataFrame:
     _set_default_session_location_if_possible(query)
     return global_session.with_default_session(
@@ -524,6 +527,7 @@ def read_gbq_query(
         index_col=index_col,
         col_order=col_order,
         max_results=max_results,
+        use_cache=use_cache,
     )
 
 
@@ -536,6 +540,7 @@ def read_gbq_table(
     index_col: Iterable[str] | str = (),
     col_order: Iterable[str] = (),
     max_results: Optional[int] = None,
+    use_cache: bool = True,
 ) -> bigframes.dataframe.DataFrame:
     _set_default_session_location_if_possible(query)
     return global_session.with_default_session(
@@ -544,6 +549,7 @@ def read_gbq_table(
         index_col=index_col,
         col_order=col_order,
         max_results=max_results,
+        use_cache=use_cache,
     )
 
 

@@ -177,6 +177,7 @@ def __init__(
         # Now that we're starting the session, don't allow the options to be
         # changed.
         context._session_started = True
+        self._df_snapshot: Dict[bigquery.TableReference, datetime.datetime] = {}
 
     @property
     def bqclient(self):
@@ -232,6 +233,7 @@ def read_gbq(
         index_col: Iterable[str] | str = (),
         col_order: Iterable[str] = (),
         max_results: Optional[int] = None,
+        use_cache: bool = True,
         # Add a verify index argument that fails if the index is not unique.
     ) -> dataframe.DataFrame:
         # TODO(b/281571214): Generate prompt to show the progress of read_gbq.
@@ -242,6 +244,7 @@ def read_gbq(
                 col_order=col_order,
                 max_results=max_results,
                 api_name="read_gbq",
+                use_cache=use_cache,
             )
         else:
             # TODO(swast): Query the snapshot table but mark it as a
@@ -253,13 +256,15 @@ def read_gbq(
                 col_order=col_order,
                 max_results=max_results,
                 api_name="read_gbq",
+                use_cache=use_cache,
             )
 
     def _query_to_destination(
         self,
         query: str,
         index_cols: List[str],
         api_name: str,
+        use_cache: bool = True,
     ) -> Tuple[Optional[bigquery.TableReference], Optional[bigquery.QueryJob]]:
         # If a dry_run indicates this is not a query type job, then don't
         # bother trying to do a CREATE TEMP TABLE ... AS SELECT ... statement.
@@ -284,6 +289,7 @@ def _query_to_destination(
         job_config = bigquery.QueryJobConfig()
         job_config.labels["bigframes-api"] = api_name
         job_config.destination = temp_table
+        job_config.use_query_cache = use_cache
 
         try:
             # Write to temp table to workaround BigQuery 10 GB query results
@@ -305,6 +311,7 @@ def read_gbq_query(
         index_col: Iterable[str] | str = (),
         col_order: Iterable[str] = (),
         max_results: Optional[int] = None,
+        use_cache: bool = True,
     ) -> dataframe.DataFrame:
         """Turn a SQL query into a DataFrame.
 
@@ -362,6 +369,7 @@ def read_gbq_query(
             col_order=col_order,
             max_results=max_results,
             api_name="read_gbq_query",
+            use_cache=use_cache,
         )
 
     def _read_gbq_query(
@@ -372,14 +380,18 @@ def _read_gbq_query(
         col_order: Iterable[str] = (),
         max_results: Optional[int] = None,
         api_name: str = "read_gbq_query",
+        use_cache: bool = True,
     ) -> dataframe.DataFrame:
         if isinstance(index_col, str):
             index_cols = [index_col]
         else:
             index_cols = list(index_col)
 
         destination, query_job = self._query_to_destination(
-            query, index_cols, api_name=api_name
+            query,
+            index_cols,
+            api_name=api_name,
+            use_cache=use_cache,
         )
 
         # If there was no destination table, that means the query must have
@@ -403,6 +415,7 @@ def _read_gbq_query(
             index_col=index_cols,
             col_order=col_order,
             max_results=max_results,
+            use_cache=use_cache,
         )
 
     def read_gbq_table(
@@ -412,6 +425,7 @@ def read_gbq_table(
         index_col: Iterable[str] | str = (),
         col_order: Iterable[str] = (),
         max_results: Optional[int] = None,
+        use_cache: bool = True,
     ) -> dataframe.DataFrame:
         """Turn a BigQuery table into a DataFrame.
 
@@ -434,33 +448,22 @@ def read_gbq_table(
             col_order=col_order,
             max_results=max_results,
             api_name="read_gbq_table",
+            use_cache=use_cache,
         )
 
     def _get_snapshot_sql_and_primary_key(
         self,
         table_ref: bigquery.table.TableReference,
         *,
         api_name: str,
+        use_cache: bool = True,
     ) -> Tuple[ibis_types.Table, Optional[Sequence[str]]]:
         """Create a read-only Ibis table expression representing a table.
 
         If we can get a total ordering from the table, such as via primary key
         column(s), then return those too so that ordering generation can be
         avoided.
         """
-        if table_ref.dataset_id.upper() == "_SESSION":
-            # _SESSION tables aren't supported by the tables.get REST API.
-            return (
-                self.ibis_client.sql(
-                    f"SELECT * FROM `_SESSION`.`{table_ref.table_id}`"
-                ),
-                None,
-            )
-        table_expression = self.ibis_client.table(
-            table_ref.table_id,
-            database=f"{table_ref.project}.{table_ref.dataset_id}",
-        )
-
         # If there are primary keys defined, the query engine assumes these
         # columns are unique, even if the constraint is not enforced. We make
         # the same assumption and use these columns as the total ordering keys.
@@ -481,14 +484,18 @@ def _get_snapshot_sql_and_primary_key(
 
         job_config = bigquery.QueryJobConfig()
         job_config.labels["bigframes-api"] = api_name
-        current_timestamp = list(
-            self.bqclient.query(
-                "SELECT CURRENT_TIMESTAMP() AS `current_timestamp`",
-                job_config=job_config,
-            ).result()
-        )[0][0]
+        if use_cache and table_ref in self._df_snapshot.keys():
+            snapshot_timestamp = self._df_snapshot[table_ref]
+        else:
+            snapshot_timestamp = list(
+                self.bqclient.query(
+                    "SELECT CURRENT_TIMESTAMP() AS `current_timestamp`",
+                    job_config=job_config,
+                ).result()
+            )[0][0]
+            self._df_snapshot[table_ref] = snapshot_timestamp
         table_expression = self.ibis_client.sql(
-            bigframes_io.create_snapshot_sql(table_ref, current_timestamp)
+            bigframes_io.create_snapshot_sql(table_ref, snapshot_timestamp)
         )
         return table_expression, primary_keys
 
@@ -500,20 +507,21 @@ def _read_gbq_table(
         col_order: Iterable[str] = (),
         max_results: Optional[int] = None,
         api_name: str,
+        use_cache: bool = True,
     ) -> dataframe.DataFrame:
         if max_results and max_results <= 0:
             raise ValueError("`max_results` should be a positive number.")
 
-        # TODO(swast): Can we re-use the temp table from other reads in the
-        # session, if the original table wasn't modified?
         table_ref = bigquery.table.TableReference.from_string(
             query, default_project=self.bqclient.project
         )
 
         (
             table_expression,
             total_ordering_cols,
-        ) = self._get_snapshot_sql_and_primary_key(table_ref, api_name=api_name)
+        ) = self._get_snapshot_sql_and_primary_key(
+            table_ref, api_name=api_name, use_cache=use_cache
+        )
 
         for key in col_order:
             if key not in table_expression.columns:

@@ -117,11 +117,6 @@ def create_snapshot_sql(
     table_ref: bigquery.TableReference, current_timestamp: datetime.datetime
 ) -> str:
     """Query a table via 'time travel' for consistent reads."""
-
-    # If we have a _SESSION table, assume that it's already a copy. Nothing to do here.
-    if table_ref.dataset_id.upper() == "_SESSION":
-        return f"SELECT * FROM `_SESSION`.`{table_ref.table_id}`"
-
     # If we have an anonymous query results table, it can't be modified and
     # there isn't any BigQuery time travel.
     if table_ref.dataset_id.startswith("_"):

@@ -16,6 +16,7 @@
 import random
 import tempfile
 import textwrap
+import time
 import typing
 from typing import List
 
@@ -308,6 +309,23 @@ def test_read_gbq_w_script_no_select(session, dataset_id: str):
     assert df["statement_type"][0] == "SCRIPT"
 
 
+def test_read_gbq_twice_with_same_timestamp(session, penguins_table_id):
+    df1 = session.read_gbq(penguins_table_id)
+    time.sleep(1)
+    df2 = session.read_gbq(penguins_table_id)
+    df1.columns = [
+        "species1",
+        "island1",
+        "culmen_length_mm1",
+        "culmen_depth_mm1",
+        "flipper_length_mm1",
+        "body_mass_g1",
+        "sex1",
+    ]
+    df3 = df1.join(df2)
+    assert df3 is not None
+
+
 def test_read_gbq_model(session, penguins_linear_model_name):
     model = session.read_gbq_model(penguins_linear_model_name)
     assert isinstance(model, bigframes.ml.linear_model.LinearRegression)

@@ -147,20 +147,6 @@ def test_create_snapshot_sql_doesnt_timetravel_anonymous_datasets():
     assert "`my-test-project`.`_e8166e0cdb`.`anonbb92cd`" in sql
 
 
-def test_create_snapshot_sql_doesnt_timetravel_session_tables():
-    table_ref = bigquery.TableReference.from_string("my-test-project._session.abcdefg")
-
-    sql = bigframes.session._io.bigquery.create_snapshot_sql(
-        table_ref, datetime.datetime.now(datetime.timezone.utc)
-    )
-
-    # We aren't modifying _SESSION tables, so don't use time travel.
-    assert "SYSTEM_TIME" not in sql
-
-    # Don't need the project ID for _SESSION tables.
-    assert "my-test-project" not in sql
-
-
 def test_create_temp_table_default_expiration():
     """Make sure the created table has an expiration."""
     bqclient = mock.create_autospec(bigquery.Client)

@@ -16,6 +16,7 @@ def read_gbq(
         index_col: Iterable[str] | str = (),
         col_order: Iterable[str] = (),
         max_results: Optional[int] = None,
+        use_cache: bool = True,
     ):
         """Loads a DataFrame from BigQuery.
 
@@ -83,6 +84,8 @@ def read_gbq(
             max_results (Optional[int], default None):
                 If set, limit the maximum number of rows to fetch from the
                 query results.
+            use_cache (bool, default True):
+                Whether to cache the query inputs. Default to True.
 
         Returns:
             bigframes.dataframe.DataFrame: A DataFrame representing results of the query or table.