Add more logging for purging

Log the number of events we will be deleting at info.

synapse/storage/events.py

@@ -2033,6 +2033,8 @@ class EventsStore(SQLBaseStore):
                 400, "topological_ordering is greater than forward extremeties"
             )
 
+        logger.debug("[purge] looking for events to delete")
+
         txn.execute(
             "SELECT event_id, state_key FROM events"
             " LEFT JOIN state_events USING (room_id, event_id)"
@@ -2041,6 +2043,14 @@ class EventsStore(SQLBaseStore):
         )
         event_rows = txn.fetchall()
 
+        to_delete = [
+            (event_id,) for event_id, state_key in event_rows
+            if state_key is None and not self.hs.is_mine_id(event_id)
+        ]
+        logger.info(
+            "[purge] found %i events before cutoff, of which %i are remote"
+            " non-state events to delete", len(event_rows), len(to_delete))
+
         for event_id, state_key in event_rows:
             txn.call_after(self._get_state_group_for_event.invalidate, (event_id,))
 
@@ -2091,6 +2101,7 @@ class EventsStore(SQLBaseStore):
         )
 
         state_rows = txn.fetchall()
+        logger.debug("[purge] found %i redundant state groups", len(state_rows))
 
         # make a set of the redundant state groups, so that we can look them up
         # efficiently
@@ -2184,10 +2195,6 @@ class EventsStore(SQLBaseStore):
         )
 
         # Delete all remote non-state events
-        to_delete = [
-            (event_id,) for event_id, state_key in event_rows
-            if state_key is None and not self.hs.is_mine_id(event_id)
-        ]
         for table in (
             "events",
             "event_json",
@@ -2203,7 +2210,7 @@ class EventsStore(SQLBaseStore):
             "event_signatures",
             "rejections",
         ):
-            logger.debug("[purge] removing non-state events from %s", table)
+            logger.debug("[purge] removing remote non-state events from %s", table)
 
             txn.executemany(
                 "DELETE FROM %s WHERE event_id = ?" % (table,),
@@ -2211,7 +2218,7 @@ class EventsStore(SQLBaseStore):
             )
 
         # Mark all state and own events as outliers
-        logger.debug("[purge] marking events as outliers")
+        logger.debug("[purge] marking remaining events as outliers")
         txn.executemany(
             "UPDATE events SET outlier = ?"
             " WHERE event_id = ?",
@@ -2221,7 +2228,7 @@ class EventsStore(SQLBaseStore):
             ]
         )
 
-        logger.debug("[purge] done")
+        logger.info("[purge] done")
 
     @defer.inlineCallbacks
     def is_event_after(self, event_id1, event_id2):