Fix batching for fetching cross-signing keys

There's no point carefully dividing a list into batches, and then completely
ignoring the batches.

synapse/storage/data_stores/main/end_to_end_keys.py

@@ -25,7 +25,9 @@ from twisted.internet import defer
 
 from synapse.logging.opentracing import log_kv, set_tag, trace
 from synapse.storage._base import SQLBaseStore, db_to_json
+from synapse.storage.database import make_in_list_sql_clause
 from synapse.util.caches.descriptors import cached, cachedList
+from synapse.util.iterutils import batch_iter
 
 
 class EndToEndKeyWorkerStore(SQLBaseStore):
@@ -391,26 +393,24 @@ class EndToEndKeyWorkerStore(SQLBaseStore):
         """
         result = {}
 
-        batch_size = 100
-        chunks = [
-            user_ids[i : i + batch_size] for i in range(0, len(user_ids), batch_size)
-        ]
-        for user_chunk in chunks:
-            sql = """
+        for user_chunk in batch_iter(user_ids, 100):
+            clause, params = make_in_list_sql_clause(
+                txn.database_engine, "k.user_id", user_chunk
+            )
+            sql = (
+                """
                 SELECT k.user_id, k.keytype, k.keydata, k.stream_id
                   FROM e2e_cross_signing_keys k
                   INNER JOIN (SELECT user_id, keytype, MAX(stream_id) AS stream_id
                                 FROM e2e_cross_signing_keys
                                GROUP BY user_id, keytype) s
                  USING (user_id, stream_id, keytype)
-                 WHERE k.user_id IN (%s)
-            """ % (
-                ",".join("?" for u in user_chunk),
+                 WHERE
+            """
+                + clause
             )
-            query_params = []
-            query_params.extend(user_chunk)
 
-            txn.execute(sql, query_params)
+            txn.execute(sql, params)
             rows = self.db.cursor_to_dict(txn)
 
             for row in rows:
@@ -453,15 +453,7 @@ class EndToEndKeyWorkerStore(SQLBaseStore):
                     device_id = k
                 devices[(user_id, device_id)] = key_type
 
-        device_list = list(devices)
-
-        # split into batches
-        batch_size = 100
-        chunks = [
-            device_list[i : i + batch_size]
-            for i in range(0, len(device_list), batch_size)
-        ]
-        for user_chunk in chunks:
+        for batch in batch_iter(devices.keys(), size=100):
             sql = """
                 SELECT target_user_id, target_device_id, key_id, signature
                   FROM e2e_cross_signing_signatures
@@ -469,11 +461,11 @@ class EndToEndKeyWorkerStore(SQLBaseStore):
                    AND (%s)
             """ % (
                 " OR ".join(
-                    "(target_user_id = ? AND target_device_id = ?)" for d in devices
+                    "(target_user_id = ? AND target_device_id = ?)" for _ in batch
                 )
             )
             query_params = [from_user_id]
-            for item in devices:
+            for item in batch:
                 # item is a (user_id, device_id) tuple
                 query_params.extend(item)