chore: add gauge for snapshots with missing snapshots (#23159)

posthog/tasks/scheduled.py

@@ -47,6 +47,7 @@
     update_quota_limiting,
     verify_persons_data_in_sync,
     update_survey_iteration,
+    invalid_web_replays,
 )
 from posthog.utils import get_crontab
 
@@ -199,6 +200,7 @@ def setup_periodic_tasks(sender: Celery, **kwargs: Any) -> None:
         pg_plugin_server_query_timing.s(),
         name="PG plugin server query timing",
     )
+
     add_periodic_task_with_expiry(
         sender,
         60,
@@ -311,3 +313,10 @@ def setup_periodic_tasks(sender: Celery, **kwargs: Any) -> None:
         check_data_import_row_limits.s(),
         name="check external data rows synced",
     )
+
+    add_periodic_task_with_expiry(
+        sender,
+        3600,
+        invalid_web_replays.s(),
+        name="Invalid web replays count",
+    )

posthog/tasks/tasks.py

@@ -228,6 +228,42 @@ def ingestion_lag() -> None:
         pass
 
 
+@shared_task(ignore_result=True)
+def invalid_web_replays() -> None:
+    from posthog.client import sync_execute
+
+    # ultimately I want to observe values by team id, but at the moment that would be lots of series, let's reduce the value first
+    query = """
+    select
+        --team_id,
+        count()
+    from (
+        select any(team_id) as team_id, argMinMerge(first_url) as first_url, argMinMerge(snapshot_source) as snapshot_source
+        from session_replay_events
+        where min_first_timestamp >= now() - interval 1 hour
+        and min_first_timestamp <= now()
+        group by session_id
+        having first_url is null and snapshot_source = 'web'
+    )
+    --group by team_id
+    """
+
+    try:
+        results = sync_execute(
+            query,
+        )
+        with pushed_metrics_registry("celery_replay_tracking") as registry:
+            gauge = Gauge(
+                "replay_tracking_web_replay_with_missing_first_url",
+                "Acts as a proxy for replay sessions which haven't received a full snapshot",
+                registry=registry,
+            )
+            count = results[0][0]
+            gauge.set(count)
+    except:
+        pass
+
+
 KNOWN_CELERY_TASK_IDENTIFIERS = {
     "pluginJob",
     "runEveryHour",