Store state groups separately from events (#2784)

* Split state group persist into seperate storage func

* Add per database engine code for state group id gen

* Move store_state_group to StateReadStore

This allows other workers to use it, and so resolve state.

* Hook up store_state_group

* Fix tests

* Rename _store_mult_state_groups_txn

* Rename StateGroupReadStore

* Remove redundant _have_persisted_state_group_txn

* Update comments

* Comment compute_event_context

* Set start val for state_group_id_seq

... otherwise we try to recreate old state groups

* Update comments

* Don't store state for outliers

* Update comment

* Update docstring as state groups are ints

1 files changed, 17 insertions, 7 deletions

diff --git a/synapse/handlers/federation.py b/synapse/handlers/federation.py

index 8ee9434c9b..643e813b1f 100644
--- a/synapse/handlers/federation.py
+++ b/synapse/handlers/federation.py
@@ -1831,8 +1831,8 @@ class FederationHandler(BaseHandler):
                 current_state = set(e.event_id for e in auth_events.values())
                 different_auth = event_auth_events - current_state
 
-                self._update_context_for_auth_events(
-                    context, auth_events, event_key,
+                yield self._update_context_for_auth_events(
+                    event, context, auth_events, event_key,
                 )
 
         if different_auth and not event.internal_metadata.is_outlier():
@@ -1913,8 +1913,8 @@ class FederationHandler(BaseHandler):
                 # 4. Look at rejects and their proofs.
                 # TODO.
 
-                self._update_context_for_auth_events(
-                    context, auth_events, event_key,
+                yield self._update_context_for_auth_events(
+                    event, context, auth_events, event_key,
                 )
 
         try:
@@ -1923,11 +1923,15 @@ class FederationHandler(BaseHandler):
             logger.warn("Failed auth resolution for %r because %s", event, e)
             raise e
 
-    def _update_context_for_auth_events(self, context, auth_events,
+    @defer.inlineCallbacks
+    def _update_context_for_auth_events(self, event, context, auth_events,
                                         event_key):
-        """Update the state_ids in an event context after auth event resolution
+        """Update the state_ids in an event context after auth event resolution,
+        storing the changes as a new state group.
 
         Args:
+            event (Event): The event we're handling the context for
+
             context (synapse.events.snapshot.EventContext): event context
                 to be updated
 
@@ -1950,7 +1954,13 @@ class FederationHandler(BaseHandler):
         context.prev_state_ids.update({
             k: a.event_id for k, a in auth_events.iteritems()
         })
-        context.state_group = self.store.get_next_state_group()
+        context.state_group = yield self.store.store_state_group(
+            event.event_id,
+            event.room_id,
+            prev_group=context.prev_group,
+            delta_ids=context.delta_ids,
+            current_state_ids=context.current_state_ids,
+        )
 
     @defer.inlineCallbacks
     def construct_auth_difference(self, local_auth, remote_auth):