Refactoring and cleanups

A few non-functional changes:

* A bunch of docstrings to document types
* Split `EventsStore._persist_events_txn` up a bit. Hopefully it's a bit more
  readable.
* Rephrase `EventFederationStore._update_min_depth_for_room_txn` to avoid
  mind-bending conditional.
* Rephrase rejected/outlier conditional in `_update_outliers_txn` to avoid
  mind-bending conditional.

1 files changed, 213 insertions, 60 deletions

diff --git a/synapse/storage/events.py b/synapse/storage/events.py
index 72319c35ae..42e433da85 100644
--- a/synapse/storage/events.py
+++ b/synapse/storage/events.py
@@ -34,14 +34,16 @@ from canonicaljson import encode_canonical_json
 from collections import deque, namedtuple, OrderedDict
 from functools import wraps
 
-import synapse
 import synapse.metrics
 
-
 import logging
 import math
 import ujson as json
 
+# these are only included to make the type annotations work
+from synapse.events import EventBase    # noqa: F401
+from synapse.events.snapshot import EventContext   # noqa: F401
+
 logger = logging.getLogger(__name__)
 
 
@@ -82,6 +84,11 @@ class _EventPeristenceQueue(object):
 
     def add_to_queue(self, room_id, events_and_contexts, backfilled):
         """Add events to the queue, with the given persist_event options.
+
+        Args:
+            room_id (str):
+            events_and_contexts (list[(EventBase, EventContext)]):
+            backfilled (bool):
         """
         queue = self._event_persist_queues.setdefault(room_id, deque())
         if queue:
@@ -227,6 +234,17 @@ class EventsStore(SQLBaseStore):
     @defer.inlineCallbacks
     @log_function
     def persist_event(self, event, context, backfilled=False):
+        """
+
+        Args:
+            event (EventBase):
+            context (EventContext):
+            backfilled (bool):
+
+        Returns:
+            Deferred: resolves to (int, int): the stream ordering of ``event``,
+            and the stream ordering of the latest persisted event
+        """
         deferred = self._event_persist_queue.add_to_queue(
             event.room_id, [(event, context)],
             backfilled=backfilled,
@@ -253,6 +271,16 @@ class EventsStore(SQLBaseStore):
     @defer.inlineCallbacks
     def _persist_events(self, events_and_contexts, backfilled=False,
                         delete_existing=False):
+        """Persist events to db
+
+        Args:
+            events_and_contexts (list[(EventBase, EventContext)]):
+            backfilled (bool):
+            delete_existing (bool):
+
+        Returns:
+            Deferred: resolves when the events have been persisted
+        """
         if not events_and_contexts:
             return
 
@@ -554,11 +582,87 @@ class EventsStore(SQLBaseStore):
         and the rejections table. Things reading from those table will need to check
         whether the event was rejected.
 
-        If delete_existing is True then existing events will be purged from the
-        database before insertion. This is useful when retrying due to IntegrityError.
+        Args:
+            txn (twisted.enterprise.adbapi.Connection): db connection
+            events_and_contexts (list[(EventBase, EventContext)]):
+                events to persist
+            backfilled (bool): True if the events were backfilled
+            delete_existing (bool): True to purge existing table rows for the
+                events from the database. This is useful when retrying due to
+                IntegrityError.
+            current_state_for_room (dict[str, (list[str], list[str])]):
+                The current-state delta for each room. For each room, a tuple
+                (to_delete, to_insert), being a list of event ids to be removed
+                from the current state, and a list of event ids to be added to
+                the current state.
+            new_forward_extremeties (dict[str, list[str]]):
+                The new forward extremities for each room. For each room, a
+                list of the event ids which are the forward extremities.
+
         """
+        self._update_current_state_txn(txn, current_state_for_room)
+
         max_stream_order = events_and_contexts[-1][0].internal_metadata.stream_ordering
-        for room_id, current_state_tuple in current_state_for_room.iteritems():
+        self._update_forward_extremities_txn(
+            txn,
+            new_forward_extremities=new_forward_extremeties,
+            max_stream_order=max_stream_order,
+        )
+
+        # Ensure that we don't have the same event twice.
+        events_and_contexts = self._filter_events_and_contexts_for_duplicates(
+            events_and_contexts,
+        )
+
+        self._update_room_depths_txn(
+            txn,
+            events_and_contexts=events_and_contexts,
+            backfilled=backfilled,
+        )
+
+        # _update_outliers_txn filters out any events which have already been
+        # persisted, and returns the filtered list.
+        events_and_contexts = self._update_outliers_txn(
+            txn,
+            events_and_contexts=events_and_contexts,
+        )
+
+        # From this point onwards the events are only events that we haven't
+        # seen before.
+
+        if delete_existing:
+            # For paranoia reasons, we go and delete all the existing entries
+            # for these events so we can reinsert them.
+            # This gets around any problems with some tables already having
+            # entries.
+            self._delete_existing_rows_txn(
+                txn,
+                events_and_contexts=events_and_contexts,
+            )
+
+        self._store_event_txn(
+            txn,
+            events_and_contexts=events_and_contexts,
+        )
+
+        # _store_rejected_events_txn filters out any events which were
+        # rejected, and returns the filtered list.
+        events_and_contexts = self._store_rejected_events_txn(
+            txn,
+            events_and_contexts=events_and_contexts,
+        )
+
+        # From this point onwards the events are only ones that weren't
+        # rejected.
+
+        self._update_metadata_tables_txn(
+            txn,
+            events_and_contexts=events_and_contexts,
+            backfilled=backfilled,
+        )
+
+    def _update_current_state_txn(self, txn, state_delta_by_room):
+        for room_id, current_state_tuple in state_delta_by_room.iteritems():
                 to_delete, to_insert = current_state_tuple
                 txn.executemany(
                     "DELETE FROM current_state_events WHERE event_id = ?",
@@ -608,7 +712,9 @@ class EventsStore(SQLBaseStore):
                     txn, self.get_current_state_ids, (room_id,)
                 )
 
-        for room_id, new_extrem in new_forward_extremeties.items():
+    def _update_forward_extremities_txn(self, txn, new_forward_extremities,
+                                        max_stream_order):
+        for room_id, new_extrem in new_forward_extremities.items():
             self._simple_delete_txn(
                 txn,
                 table="event_forward_extremities",
@@ -626,7 +732,7 @@ class EventsStore(SQLBaseStore):
                     "event_id": ev_id,
                     "room_id": room_id,
                 }
-                for room_id, new_extrem in new_forward_extremeties.items()
+                for room_id, new_extrem in new_forward_extremities.items()
                 for ev_id in new_extrem
             ],
         )
@@ -643,13 +749,22 @@ class EventsStore(SQLBaseStore):
                     "event_id": event_id,
                     "stream_ordering": max_stream_order,
                 }
-                for room_id, new_extrem in new_forward_extremeties.items()
+                for room_id, new_extrem in new_forward_extremities.items()
                 for event_id in new_extrem
             ]
         )
 
-        # Ensure that we don't have the same event twice.
-        # Pick the earliest non-outlier if there is one, else the earliest one.
+    @classmethod
+    def _filter_events_and_contexts_for_duplicates(cls, events_and_contexts):
+        """Ensure that we don't have the same event twice.
+
+        Pick the earliest non-outlier if there is one, else the earliest one.
+
+        Args:
+            events_and_contexts (list[(EventBase, EventContext)]):
+        Returns:
+            list[(EventBase, EventContext)]: filtered list
+        """
         new_events_and_contexts = OrderedDict()
         for event, context in events_and_contexts:
             prev_event_context = new_events_and_contexts.get(event.event_id)
@@ -662,9 +777,17 @@ class EventsStore(SQLBaseStore):
                         new_events_and_contexts[event.event_id] = (event, context)
             else:
                 new_events_and_contexts[event.event_id] = (event, context)
+        return new_events_and_contexts.values()
 
-        events_and_contexts = new_events_and_contexts.values()
+    def _update_room_depths_txn(self, txn, events_and_contexts, backfilled):
+        """Update min_depth for each room
 
+        Args:
+            txn (twisted.enterprise.adbapi.Connection): db connection
+            events_and_contexts (list[(EventBase, EventContext)]): events
+                we are persisting
+            backfilled (bool): True if the events were backfilled
+        """
         depth_updates = {}
         for event, context in events_and_contexts:
             # Remove the any existing cache entries for the event_ids
@@ -683,6 +806,21 @@ class EventsStore(SQLBaseStore):
         for room_id, depth in depth_updates.items():
             self._update_min_depth_for_room_txn(txn, room_id, depth)
 
+    def _update_outliers_txn(self, txn, events_and_contexts):
+        """Update any outliers with new event info.
+
+        This turns outliers into ex-outliers (unless the new event was
+        rejected).
+
+        Args:
+            txn (twisted.enterprise.adbapi.Connection): db connection
+            events_and_contexts (list[(EventBase, EventContext)]): events
+                we are persisting
+
+        Returns:
+            list[(EventBase, EventContext)] new list, without events which
+            are already in the events table.
+        """
         txn.execute(
             "SELECT event_id, outlier FROM events WHERE event_id in (%s)" % (
                 ",".join(["?"] * len(events_and_contexts)),
@@ -697,19 +835,16 @@ class EventsStore(SQLBaseStore):
 
         to_remove = set()
         for event, context in events_and_contexts:
-            if context.rejected:
-                # If the event is rejected then we don't care if the event
-                # was an outlier or not.
-                if event.event_id in have_persisted:
-                    # If we have already seen the event then ignore it.
-                    to_remove.add(event)
-                continue
-
             if event.event_id not in have_persisted:
                 continue
 
             to_remove.add(event)
 
+            if context.rejected:
+                # If the event is rejected then we don't care if the event
+                # was an outlier or not.
+                continue
+
             outlier_persisted = have_persisted[event.event_id]
             if not event.internal_metadata.is_outlier() and outlier_persisted:
                 # We received a copy of an event that we had already stored as
@@ -764,37 +899,19 @@ class EventsStore(SQLBaseStore):
                 # event isn't an outlier any more.
                 self._update_backward_extremeties(txn, [event])
 
-        events_and_contexts = [
+        return [
             ec for ec in events_and_contexts if ec[0] not in to_remove
         ]
 
+    @classmethod
+    def _delete_existing_rows_txn(cls, txn, events_and_contexts):
         if not events_and_contexts:
-            # Make sure we don't pass an empty list to functions that expect to
-            # be storing at least one element.
+            # nothing to do here
             return
 
-        # From this point onwards the events are only events that we haven't
-        # seen before.
+        logger.info("Deleting existing")
 
-        def event_dict(event):
-            return {
-                k: v
-                for k, v in event.get_dict().items()
-                if k not in [
-                    "redacted",
-                    "redacted_because",
-                ]
-            }
-
-        if delete_existing:
-            # For paranoia reasons, we go and delete all the existing entries
-            # for these events so we can reinsert them.
-            # This gets around any problems with some tables already having
-            # entries.
-
-            logger.info("Deleting existing")
-
-            for table in (
+        for table in (
                 "events",
                 "event_auth",
                 "event_json",
@@ -817,11 +934,34 @@ class EventsStore(SQLBaseStore):
                 "redactions",
                 "room_memberships",
                 "topics"
-            ):
-                txn.executemany(
-                    "DELETE FROM %s WHERE event_id = ?" % (table,),
-                    [(ev.event_id,) for ev, _ in events_and_contexts]
-                )
+        ):
+            txn.executemany(
+                "DELETE FROM %s WHERE event_id = ?" % (table,),
+                [(ev.event_id,) for ev, _ in events_and_contexts]
+            )
+
+    def _store_event_txn(self, txn, events_and_contexts):
+        """Insert new events into the event and event_json tables
+
+        Args:
+            txn (twisted.enterprise.adbapi.Connection): db connection
+            events_and_contexts (list[(EventBase, EventContext)]): events
+                we are persisting
+        """
+
+        if not events_and_contexts:
+            # nothing to do here
+            return
+
+        def event_dict(event):
+            return {
+                k: v
+                for k, v in event.get_dict().items()
+                if k not in [
+                    "redacted",
+                    "redacted_because",
+                ]
+            }
 
         self._simple_insert_many_txn(
             txn,
@@ -865,6 +1005,19 @@ class EventsStore(SQLBaseStore):
             ],
         )
 
+    def _store_rejected_events_txn(self, txn, events_and_contexts):
+        """Add rows to the 'rejections' table for received events which were
+        rejected
+
+        Args:
+            txn (twisted.enterprise.adbapi.Connection): db connection
+            events_and_contexts (list[(EventBase, EventContext)]): events
+                we are persisting
+
+        Returns:
+            list[(EventBase, EventContext)] new list, without the rejected
+                events.
+        """
         # Remove the rejected events from the list now that we've added them
         # to the events table and the events_json table.
         to_remove = set()
@@ -876,17 +1029,24 @@ class EventsStore(SQLBaseStore):
                 )
                 to_remove.add(event)
 
-        events_and_contexts = [
+        return [
             ec for ec in events_and_contexts if ec[0] not in to_remove
         ]
 
+    def _update_metadata_tables_txn(self, txn, events_and_contexts, backfilled):
+        """Update all the miscellaneous tables for new events
+
+        Args:
+            txn (twisted.enterprise.adbapi.Connection): db connection
+            events_and_contexts (list[(EventBase, EventContext)]): events
+                we are persisting
+            backfilled (bool): True if the events were backfilled
+        """
+
         if not events_and_contexts:
-            # Make sure we don't pass an empty list to functions that expect to
-            # be storing at least one element.
+            # nothing to do here
             return
 
-        # From this point onwards the events are only ones that weren't rejected.
-
         for event, context in events_and_contexts:
             # Insert all the push actions into the event_push_actions table.
             if context.push_actions:
@@ -1005,13 +1165,6 @@ class EventsStore(SQLBaseStore):
         # Prefill the event cache
         self._add_to_cache(txn, events_and_contexts)
 
-        if backfilled:
-            # Backfilled events come before the current state so we don't need
-            # to update the current state table
-            return
-
-        return
-
     def _add_to_cache(self, txn, events_and_contexts):
         to_prefill = []