Disable calculating unread counts unless the config flag is enabled. (#13694)

This avoids doing work that will never be used (since the
resulting unread counts will never be sent in a /sync
response).

The negative of doing this is that unread counts will be
incorrect when the feature is initially enabled.

2 files changed, 9 insertions, 1 deletions

diff --git a/synapse/config/experimental.py b/synapse/config/experimental.py
index 260db49cad..702b81e636 100644
--- a/synapse/config/experimental.py
+++ b/synapse/config/experimental.py
@@ -71,6 +71,9 @@ class ExperimentalConfig(Config):
         self.msc3720_enabled: bool = experimental.get("msc3720_enabled", False)
 
         # MSC2654: Unread counts
+        #
+        # Note that enabling this will result in an incorrect unread count for
+        # previously calculated push actions.
         self.msc2654_enabled: bool = experimental.get("msc2654_enabled", False)
 
         # MSC2815 (allow room moderators to view redacted event content)
diff --git a/synapse/push/bulk_push_rule_evaluator.py b/synapse/push/bulk_push_rule_evaluator.py
index ccd512be54..d1caf8a0f7 100644
--- a/synapse/push/bulk_push_rule_evaluator.py
+++ b/synapse/push/bulk_push_rule_evaluator.py
@@ -262,7 +262,12 @@ class BulkPushRuleEvaluator:
             # This can happen due to out of band memberships
             return
 
-        count_as_unread = _should_count_as_unread(event, context)
+        # Disable counting as unread unless the experimental configuration is
+        # enabled, as it can cause additional (unwanted) rows to be added to the
+        # event_push_actions table.
+        count_as_unread = False
+        if self.hs.config.experimental.msc2654_enabled:
+            count_as_unread = _should_count_as_unread(event, context)
 
         rules_by_user = await self._get_rules_for_event(event)
         actions_by_user: Dict[str, Collection[Union[Mapping, str]]] = {}