zilencer: Add client-size rate limiting of analytics upload.

This should help both by avoiding high memory usage causing OOM kills
on the client, as well as timeouts causing an exception email to be
sent.

zerver/lib/remote_server.py

@@ -92,12 +92,16 @@ def send_json_to_push_bouncer(method: str, endpoint: str, post_data: Dict[str, A
 def build_analytics_data(realm_count_query: Any,
                          installation_count_query: Any) -> Tuple[List[Dict[str, Any]],
                                                                  List[Dict[str, Any]]]:
+    # We limit the batch size on the client side to avoid OOM kills timeouts, etc.
+    MAX_CLIENT_BATCH_SIZE = 10000
     data = {}
     data['analytics_realmcount'] = [
-        model_to_dict(realm_count) for realm_count in realm_count_query.order_by("id")
+        model_to_dict(realm_count) for realm_count in
+        realm_count_query.order_by("id")[0:MAX_CLIENT_BATCH_SIZE]
     ]
     data['analytics_installationcount'] = [
-        model_to_dict(count) for count in installation_count_query.order_by("id")
+        model_to_dict(count) for count in
+        installation_count_query.order_by("id")[0:MAX_CLIENT_BATCH_SIZE]
     ]
 
     floatify_datetime_fields(data, 'analytics_realmcount')