perf: Reduce CURRENT_TIMESTAMP queries

bigframes/session/_io/bigquery/read_gbq_table.py

@@ -45,8 +45,8 @@
 def get_table_metadata(
     bqclient: bigquery.Client,
     table_ref: google.cloud.bigquery.table.TableReference,
+    bq_time: datetime.datetime,
     *,
-    api_name: str,
     cache: Dict[bigquery.TableReference, Tuple[datetime.datetime, bigquery.Table]],
     use_cache: bool = True,
 ) -> Tuple[datetime.datetime, google.cloud.bigquery.table.Table]:
@@ -76,23 +76,9 @@ def get_table_metadata(
         )
         return cached_table
 
-    # TODO(swast): It's possible that the table metadata is changed between now
-    # and when we run the CURRENT_TIMESTAMP() query to see when we can time
-    # travel to. Find a way to fetch the table metadata and BQ's current time
-    # atomically.
     table = bqclient.get_table(table_ref)
 
-    # TODO(swast): Use session._start_query instead?
-    # TODO(swast): Use query_and_wait since we know these are small results.
-    job_config = bigquery.QueryJobConfig()
-    bigframes.session._io.bigquery.add_labels(job_config, api_name=api_name)
-    snapshot_timestamp = list(
-        bqclient.query(
-            "SELECT CURRENT_TIMESTAMP() AS `current_timestamp`",
-            job_config=job_config,
-        ).result()
-    )[0][0]
-    cached_table = (snapshot_timestamp, table)
+    cached_table = (bq_time, table)
     cache[table_ref] = cached_table
     return cached_table
 

bigframes/session/loader.py

@@ -59,6 +59,7 @@
 import bigframes.session.metrics
 import bigframes.session.planner
 import bigframes.session.temp_storage
+import bigframes.session.time as session_time
 import bigframes.version
 
 # Avoid circular imports.
@@ -128,6 +129,8 @@ def __init__(
         self._metrics = metrics
         # Unfortunate circular reference, but need to pass reference when constructing objects
         self._session = session
+        self._clock = session_time.BigQuerySyncedClock(bqclient)
+        self._clock.sync()
 
     def read_pandas_load_job(
         self, pandas_dataframe: pandas.DataFrame, api_name: str
@@ -246,7 +249,7 @@ def read_gbq_table(
         time_travel_timestamp, table = bf_read_gbq_table.get_table_metadata(
             self._bqclient,
             table_ref=table_ref,
-            api_name=api_name,
+            bq_time=self._clock.get_time(),
             cache=self._df_snapshot,
             use_cache=use_cache,
         )

bigframes/session/time.py

@@ -0,0 +1,59 @@
+# Copyright 2024 Google LLC
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+import datetime
+import threading
+import time
+from typing import cast, Optional
+
+import google.cloud.bigquery as bigquery
+
+MIN_RESYNC_SECONDS = 100
+
+
+class BigQuerySyncedClock:
+    """
+    Local clock that attempts to synchronize its time with the bigquery service.
+    """
+
+    def __init__(self, bqclient: bigquery.Client):
+        self._bqclient = bqclient
+        self._sync_lock = threading.Lock()
+        self._sync_remote_time: Optional[datetime.datetime] = None
+        self._sync_monotonic_time: Optional[float] = None
+
+    def get_time(self):
+        if (self._sync_monotonic_time is None) or (self._sync_remote_time is None):
+            self.sync()
+        assert self._sync_remote_time is not None
+        assert self._sync_monotonic_time is not None
+        return self._sync_remote_time + datetime.timedelta(
+            seconds=time.monotonic() - self._sync_monotonic_time
+        )
+
+    def sync(self):
+        with self._sync_lock:
+            if (self._sync_monotonic_time is not None) and (
+                time.monotonic() - self._sync_monotonic_time
+            ) < MIN_RESYNC_SECONDS:
+                return
+            current_bq_time = list(
+                next(
+                    self._bqclient.query_and_wait(
+                        "SELECT CURRENT_TIMESTAMP() AS `current_timestamp`",
+                    )
+                )
+            )[0]
+            self._sync_remote_time = cast(datetime.datetime, current_bq_time)
+            self._sync_monotonic_time = time.monotonic()

noxfile.py

@@ -51,6 +51,7 @@
 UNIT_TEST_STANDARD_DEPENDENCIES = [
     "mock",
     "asyncmock",
+    "freezegun",
     PYTEST_VERSION,
     "pytest-cov",
     "pytest-asyncio",

tests/unit/resources.py

@@ -91,7 +91,16 @@ def query_mock(query, *args, **kwargs):
 
         return query_job
 
+    existing_query_and_wait = bqclient.query_and_wait
+
+    def query_and_wait_mock(query, *args, **kwargs):
+        if query.startswith("SELECT CURRENT_TIMESTAMP()"):
+            return iter([[datetime.datetime.now()]])
+        else:
+            return existing_query_and_wait(query, *args, **kwargs)
+
     bqclient.query = query_mock
+    bqclient.query_and_wait = query_and_wait_mock
 
     clients_provider = mock.create_autospec(bigframes.session.clients.ClientsProvider)
     type(clients_provider).bqclient = mock.PropertyMock(return_value=bqclient)

tests/unit/session/test_time.py

@@ -0,0 +1,69 @@
+# Copyright 2024 Google LLC
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+import datetime
+import unittest.mock as mock
+
+import freezegun
+import google.cloud.bigquery
+import pytest
+
+import bigframes.session.time
+
+INITIAL_BQ_TIME = datetime.datetime(
+    year=2020,
+    month=4,
+    day=24,
+    hour=8,
+    minute=55,
+    second=29,
+    tzinfo=datetime.timezone.utc,
+)
+
+
+@pytest.fixture()
+def bq_client():
+    bqclient = mock.create_autospec(google.cloud.bigquery.Client, instance=True)
+
+    def query_and_wait_mock(query, *args, **kwargs):
+        if query.startswith("SELECT CURRENT_TIMESTAMP()"):
+            return iter([[INITIAL_BQ_TIME]])
+        else:
+            return ValueError(f"mock cannot handle query : {query}")
+
+    bqclient.query_and_wait = query_and_wait_mock
+    return bqclient
+
+
+def test_bqsyncedclock_get_time(bq_client):
+    # this initial local time is actually irrelevant, only the ticks matter
+    initial_local_datetime = datetime.datetime(
+        year=1, month=7, day=12, hour=15, minute=6, second=3
+    )
+
+    with freezegun.freeze_time(initial_local_datetime) as frozen_datetime:
+        clock = bigframes.session.time.BigQuerySyncedClock(bq_client)
+
+        t1 = clock.get_time()
+        assert t1 == INITIAL_BQ_TIME
+
+        frozen_datetime.tick(datetime.timedelta(seconds=3))
+        t2 = clock.get_time()
+        assert t2 == INITIAL_BQ_TIME + datetime.timedelta(seconds=3)
+
+        frozen_datetime.tick(datetime.timedelta(seconds=23529385))
+        t3 = clock.get_time()
+        assert t3 == INITIAL_BQ_TIME + datetime.timedelta(
+            seconds=3
+        ) + datetime.timedelta(seconds=23529385)