Only turn on the twisted deferred debugging if full_twisted_stacktraces is set in the config

synapse/app/homeserver.py

@@ -33,9 +33,6 @@ if __name__ == '__main__':
         sys.stderr.writelines(message)
         sys.exit(1)
 
-    from synapse.util.debug import debug_deferreds
-    debug_deferreds()
-
 from synapse.storage.engines import create_engine, IncorrectDatabaseSetup
 from synapse.storage import are_all_users_on_domain
 from synapse.storage.prepare_database import UpgradeDatabaseException

synapse/config/logger.py

@@ -22,6 +22,7 @@ import yaml
 from string import Template
 import os
 import signal
+from synapse.util.debug import debug_deferreds
 
 
 DEFAULT_LOG_CONFIG = Template("""
@@ -69,6 +70,8 @@ class LoggingConfig(Config):
         self.verbosity = config.get("verbose", 0)
         self.log_config = self.abspath(config.get("log_config"))
         self.log_file = self.abspath(config.get("log_file"))
+        if config.get("full_twisted_stacktraces"):
+            debug_deferreds()
 
     def default_config(self, config_dir_path, server_name, **kwargs):
         log_file = self.abspath("homeserver.log")
@@ -84,6 +87,11 @@ class LoggingConfig(Config):
 
         # A yaml python logging config file
         log_config: "%(log_config)s"
+
+        # Stop twisted from discarding the stack traces of exceptions in
+        # deferreds by waiting a reactor tick before running a deferred's
+        # callbacks.
+        # full_twisted_stacktraces: true
         """ % locals()
 
     def read_arguments(self, args):