From e6a6c4fbab8f409a20422659dddc3b7437a2cc07 Mon Sep 17 00:00:00 2001
From: Richard van der Hoff <richard@matrix.org>
Date: Wed, 24 Jul 2019 16:37:50 +0100
Subject: [PATCH] split _get_events_from_db out of _enqueue_events

---
 synapse/storage/events_worker.py | 83 ++++++++++++++++++++------------
 1 file changed, 51 insertions(+), 32 deletions(-)

diff --git a/synapse/storage/events_worker.py b/synapse/storage/events_worker.py
index 5b606bec7c..6e5f1cf6ee 100644
--- a/synapse/storage/events_worker.py
+++ b/synapse/storage/events_worker.py
@@ -343,13 +343,12 @@ class EventsWorkerStore(SQLBaseStore):
             log_ctx = LoggingContext.current_context()
             log_ctx.record_event_fetch(len(missing_events_ids))
 
-            # Note that _enqueue_events is also responsible for turning db rows
+            # Note that _get_events_from_db is also responsible for turning db rows
             # into FrozenEvents (via _get_event_from_row), which involves seeing if
             # the events have been redacted, and if so pulling the redaction event out
             # of the database to check it.
             #
-            # _enqueue_events is a bit of a rubbish name but naming is hard.
-            missing_events = yield self._enqueue_events(
+            missing_events = yield self._get_events_from_db(
                 missing_events_ids, allow_rejected=allow_rejected
             )
 
@@ -458,43 +457,25 @@ class EventsWorkerStore(SQLBaseStore):
                     self.hs.get_reactor().callFromThread(fire, event_list, e)
 
     @defer.inlineCallbacks
-    def _enqueue_events(self, events, allow_rejected=False):
-        """Fetches events from the database using the _event_fetch_list. This
-        allows batch and bulk fetching of events - it allows us to fetch events
-        without having to create a new transaction for each request for events.
+    def _get_events_from_db(self, event_ids, allow_rejected=False):
+        """Fetch a bunch of events from the database.
+
+        Returned events will be added to the cache for future lookups.
 
         Args:
-            events (Iterable[str]): events to be fetched.
+            event_ids (Iterable[str]): The event_ids of the events to fetch
+            allow_rejected (bool): Whether to include rejected events
 
         Returns:
-            Deferred[Dict[str, _EventCacheEntry]]: map from event id to result.
+            Deferred[Dict[str, _EventCacheEntry]]:
+                map from event id to result.
         """
-        if not events:
+        if not event_ids:
             return {}
 
-        events_d = defer.Deferred()
-        with self._event_fetch_lock:
-            self._event_fetch_list.append((events, events_d))
+        row_map = yield self._enqueue_events(event_ids)
 
-            self._event_fetch_lock.notify()
-
-            if self._event_fetch_ongoing < EVENT_QUEUE_THREADS:
-                self._event_fetch_ongoing += 1
-                should_start = True
-            else:
-                should_start = False
-
-        if should_start:
-            run_as_background_process(
-                "fetch_events", self.runWithConnection, self._do_fetch
-            )
-
-        logger.debug("Loading %d events", len(events))
-        with PreserveLoggingContext():
-            row_map = yield events_d
-        logger.debug("Loaded %d events (%d rows)", len(events), len(row_map))
-
-        rows = (row_map.get(event_id) for event_id in events)
+        rows = (row_map.get(event_id) for event_id in event_ids)
 
         # filter out absent rows
         rows = filter(operator.truth, rows)
@@ -521,6 +502,44 @@ class EventsWorkerStore(SQLBaseStore):
 
         return {e.event.event_id: e for e in res if e}
 
+    @defer.inlineCallbacks
+    def _enqueue_events(self, events):
+        """Fetches events from the database using the _event_fetch_list. This
+        allows batch and bulk fetching of events - it allows us to fetch events
+        without having to create a new transaction for each request for events.
+
+        Args:
+            events (Iterable[str]): events to be fetched.
+
+        Returns:
+            Deferred[Dict[str, Dict]]: map from event id to row data from the database.
+                May contain events that weren't requested.
+        """
+
+        events_d = defer.Deferred()
+        with self._event_fetch_lock:
+            self._event_fetch_list.append((events, events_d))
+
+            self._event_fetch_lock.notify()
+
+            if self._event_fetch_ongoing < EVENT_QUEUE_THREADS:
+                self._event_fetch_ongoing += 1
+                should_start = True
+            else:
+                should_start = False
+
+        if should_start:
+            run_as_background_process(
+                "fetch_events", self.runWithConnection, self._do_fetch
+            )
+
+        logger.debug("Loading %d events: %s", len(events), events)
+        with PreserveLoggingContext():
+            row_map = yield events_d
+        logger.debug("Loaded %d events (%d rows)", len(events), len(row_map))
+
+        return row_map
+
     def _fetch_event_rows(self, txn, event_ids):
         """Fetch event rows from the database