DB: do not fetch data and others when deleting rows (#10446)

* DB: do not fetch `data` and others when deleting rows

This task was cancelled again. The query shows a SELECT first that fetchs the
whole rows. I think we can reduce this time/memory by only fetching the ids.

* DB: only fetch "id" when deleting rows

* DB: clean up old data using raw SQL from Django

We are facing an issue with this query because it takes too long to
execute (more than 30s) making our DB to kill the query. This is because Django
performs a `SELECT` first to be able to trigger pre_ and post_ delete signals on
each object delete.

We don't really need this here, so we are using raw SQL to bypass this and make
the query to execute faster. This is not ideal, but we didn't find a better approach.

* DB: there is no results to fetch

The query is executed without requiring `.fetchall()`

readthedocs/analytics/tasks.py

@@ -1,12 +1,12 @@
 """Tasks for Read the Docs' analytics."""
 
 from django.conf import settings
+from django.db import connection
 from django.utils import timezone
 
 import readthedocs
 from readthedocs.worker import app
 
-from .models import PageView
 from .utils import send_to_analytics
 
 DEFAULT_PARAMETERS = {
@@ -80,7 +80,16 @@ def delete_old_page_counts():
     """
     retention_days = settings.RTD_ANALYTICS_DEFAULT_RETENTION_DAYS
     days_ago = timezone.now().date() - timezone.timedelta(days=retention_days)
-    return PageView.objects.filter(
-        date__lt=days_ago,
-        date__gt=days_ago - timezone.timedelta(days=90),
-    ).delete()
+
+    # NOTE: we are using raw SQL here to avoid Django doing a SELECT first to
+    # send `pre_` and `post_` delete signals
+    # See https://docs.djangoproject.com/en/4.2/ref/models/querysets/#delete
+    with connection.cursor() as cursor:
+        cursor.execute(
+            # "SELECT COUNT(*) FROM analytics_pageview WHERE date BETWEEN %s AND %s",
+            "DELETE FROM analytics_pageview WHERE date BETWEEN %s AND %s",
+            [
+                days_ago - timezone.timedelta(days=90),
+                days_ago,
+            ],
+        )

readthedocs/telemetry/tasks.py

@@ -1,6 +1,7 @@
 """Tasks related to telemetry."""
 
 from django.conf import settings
+from django.db import connections
 from django.utils import timezone
 
 from readthedocs.builds.models import Build
@@ -33,7 +34,15 @@ def delete_old_build_data():
     """
     retention_days = settings.RTD_TELEMETRY_DATA_RETENTION_DAYS
     days_ago = timezone.now().date() - timezone.timedelta(days=retention_days)
-    return BuildData.objects.filter(
-        created__lt=days_ago,
-        created__gt=days_ago - timezone.timedelta(days=90),
-    ).delete()
+    # NOTE: we are using raw SQL here to avoid Django doing a SELECT first to
+    # send `pre_` and `post_` delete signals
+    # See https://docs.djangoproject.com/en/4.2/ref/models/querysets/#delete
+    with connections["telemetry"].cursor() as cursor:
+        cursor.execute(
+            # "SELECT COUNT(*) FROM telemetry_builddata WHERE created BETWEEN %s AND %s",
+            "DELETE FROM telemetry_builddata WHERE created BETWEEN %s AND %s",
+            [
+                days_ago - timezone.timedelta(days=90),
+                days_ago,
+            ],
+        )