Merge pull request #754 from matrix-org/markjh/check_for_nop

Check that something has happend before running the selects

3 files changed, 14 insertions, 2 deletions

diff --git a/synapse/storage/events.py b/synapse/storage/events.py
index 21487724ed..0307b2af3c 100644
--- a/synapse/storage/events.py
+++ b/synapse/storage/events.py
@@ -1143,6 +1143,12 @@ class EventsStore(SQLBaseStore):
                            current_backfill_id, current_forward_id, limit):
         """Get all the new events that have arrived at the server either as
         new events or as backfilled events"""
+        have_backfill_events = last_backfill_id != current_backfill_id
+        have_forward_events = last_forward_id != current_forward_id
+
+        if not have_backfill_events and not have_forward_events:
+            return defer.succeed(AllNewEventsResult([], [], [], [], []))
+
         def get_all_new_events_txn(txn):
             sql = (
                 "SELECT e.stream_ordering, ej.internal_metadata, ej.json, eg.state_group"
@@ -1155,7 +1161,7 @@ class EventsStore(SQLBaseStore):
                 " ORDER BY e.stream_ordering ASC"
                 " LIMIT ?"
             )
-            if last_forward_id != current_forward_id:
+            if have_forward_events:
                 txn.execute(sql, (last_forward_id, current_forward_id, limit))
                 new_forward_events = txn.fetchall()
 
@@ -1199,7 +1205,7 @@ class EventsStore(SQLBaseStore):
                 " ORDER BY e.stream_ordering DESC"
                 " LIMIT ?"
             )
-            if last_backfill_id != current_backfill_id:
+            if have_backfill_events:
                 txn.execute(sql, (-last_backfill_id, -current_backfill_id, limit))
                 new_backfill_events = txn.fetchall()
 
diff --git a/synapse/storage/pusher.py b/synapse/storage/pusher.py
index e5755c0aea..11feb3eb11 100644
--- a/synapse/storage/pusher.py
+++ b/synapse/storage/pusher.py
@@ -106,6 +106,9 @@ class PusherStore(SQLBaseStore):
         return self._pushers_id_gen.get_current_token()
 
     def get_all_updated_pushers(self, last_id, current_id, limit):
+        if last_id == current_id:
+            return defer.succeed(([], []))
+
         def get_all_updated_pushers_txn(txn):
             sql = (
                 "SELECT id, user_name, access_token, profile_tag, kind,"
diff --git a/synapse/storage/receipts.py b/synapse/storage/receipts.py
index 3b8805593e..935fc503d9 100644
--- a/synapse/storage/receipts.py
+++ b/synapse/storage/receipts.py
@@ -391,6 +391,9 @@ class ReceiptsStore(SQLBaseStore):
         )
 
     def get_all_updated_receipts(self, last_id, current_id, limit=None):
+        if last_id == current_id:
+            return defer.succeed([])
+
         def get_all_updated_receipts_txn(txn):
             sql = (
                 "SELECT stream_id, room_id, receipt_type, user_id, event_id, data"