fix: event listener (#2119)

* fix: commit transaction after taking event

* feat: allow to reconnect to postgres for event listener

* chore: log sync events pending to process to metrics

* fix: make dead_letter runner able to process events without needing to have lock on the event

* chore: close Session after reconnect

* refactor: make EventSource emit only events that can be processed

app/models.py

@@ -3699,7 +3699,10 @@ class SyncEvent(Base, ModelMixin):
           AND taken_time IS NULL
         """
         args = {"taken_time": arrow.now().datetime, "sync_event_id": self.id}
+
         res = Session.execute(sql, args)
+        Session.commit()
+
         return res.rowcount > 0
 
     @classmethod

events/event_source.py

@@ -13,6 +13,8 @@ from typing import Callable, NoReturn
 _DEAD_LETTER_THRESHOLD_MINUTES = 10
 _DEAD_LETTER_INTERVAL_SECONDS = 30
 
+_POSTGRES_RECONNECT_INTERVAL_SECONDS = 5
+
 
 class EventSource(ABC):
     @abstractmethod
@@ -22,9 +24,19 @@ class EventSource(ABC):
 
 class PostgresEventSource(EventSource):
     def __init__(self, connection_string: str):
-        self.__connection = psycopg2.connect(connection_string)
+        self.__connection_string = connection_string
+        self.__connect()
 
     def run(self, on_event: Callable[[SyncEvent], NoReturn]):
+        while True:
+            try:
+                self.__listen(on_event)
+            except Exception as e:
+                LOG.warn(f"Error listening to events: {e}")
+                sleep(_POSTGRES_RECONNECT_INTERVAL_SECONDS)
+                self.__connect()
+
+    def __listen(self, on_event: Callable[[SyncEvent], NoReturn]):
         self.__connection.set_isolation_level(
             psycopg2.extensions.ISOLATION_LEVEL_AUTOCOMMIT
         )
@@ -44,12 +56,24 @@ class PostgresEventSource(EventSource):
                         webhook_id = int(notify.payload)
                         event = SyncEvent.get_by(id=webhook_id)
                         if event is not None:
-                            on_event(event)
+                            if event.mark_as_taken():
+                                on_event(event)
+                            else:
+                                LOG.info(
+                                    f"Event {event.id} was handled by another runner"
+                                )
                         else:
                             LOG.info(f"Could not find event with id={notify.payload}")
                     except Exception as e:
                         LOG.warn(f"Error getting event: {e}")
 
+    def __connect(self):
+        self.__connection = psycopg2.connect(self.__connection_string)
+
+        from app.db import Session
+
+        Session.close()
+
 
 class DeadLetterEventSource(EventSource):
     @newrelic.agent.background_task()
@@ -73,3 +97,4 @@ class DeadLetterEventSource(EventSource):
                     sleep(_DEAD_LETTER_INTERVAL_SECONDS)
             except Exception as e:
                 LOG.warn(f"Error getting dead letter event: {e}")
+                sleep(_DEAD_LETTER_INTERVAL_SECONDS)

events/runner.py

@@ -18,31 +18,25 @@ class Runner:
     @newrelic.agent.background_task()
     def __on_event(self, event: SyncEvent):
         try:
-            can_process = event.mark_as_taken()
-            if can_process:
-                event_created_at = event.created_at
-                start_time = arrow.now()
-                success = self.__sink.process(event)
-                if success:
-                    event_id = event.id
-                    SyncEvent.delete(event.id, commit=True)
-                    LOG.info(f"Marked {event_id} as done")
+            event_created_at = event.created_at
+            start_time = arrow.now()
+            success = self.__sink.process(event)
+            if success:
+                event_id = event.id
+                SyncEvent.delete(event.id, commit=True)
+                LOG.info(f"Marked {event_id} as done")
 
-                    end_time = arrow.now() - start_time
-                    time_between_taken_and_created = start_time - event_created_at
+                end_time = arrow.now() - start_time
+                time_between_taken_and_created = start_time - event_created_at
 
-                    newrelic.agent.record_custom_metric(
-                        "Custom/sync_event_processed", 1
-                    )
-                    newrelic.agent.record_custom_metric(
-                        "Custom/sync_event_process_time", end_time.total_seconds()
-                    )
-                    newrelic.agent.record_custom_metric(
-                        "Custom/sync_event_elapsed_time",
-                        time_between_taken_and_created.total_seconds(),
-                    )
-            else:
-                LOG.info(f"{event.id} was handled by another runner")
+                newrelic.agent.record_custom_metric("Custom/sync_event_processed", 1)
+                newrelic.agent.record_custom_metric(
+                    "Custom/sync_event_process_time", end_time.total_seconds()
+                )
+                newrelic.agent.record_custom_metric(
+                    "Custom/sync_event_elapsed_time",
+                    time_between_taken_and_created.total_seconds(),
+                )
         except Exception as e:
             LOG.warn(f"Exception processing event [id={event.id}]: {e}")
             newrelic.agent.record_custom_metric("Custom/sync_event_failed", 1)

monitoring.py

@@ -93,11 +93,23 @@ def log_nb_db_connection():
     newrelic.agent.record_custom_metric("Custom/nb_db_connections", nb_connection)
 
 
+@newrelic.agent.background_task()
+def log_pending_to_process_events():
+    r = Session.execute("select count(*) from sync_events WHERE taken_time IS NULL;")
+    events_pending = list(r)[0][0]
+
+    LOG.d("number of events pending to process %s", events_pending)
+    newrelic.agent.record_custom_metric(
+        "Custom/sync_events_pending_to_process", events_pending
+    )
+
+
 if __name__ == "__main__":
     exporter = MetricExporter(get_newrelic_license())
     while True:
         log_postfix_metrics()
         log_nb_db_connection()
+        log_pending_to_process_events()
         Session.close()
 
         exporter.run()