diff --git a/vcsserver/lib/rc_cache/backends.py b/vcsserver/lib/rc_cache/backends.py
--- a/vcsserver/lib/rc_cache/backends.py
+++ b/vcsserver/lib/rc_cache/backends.py
@@ -32,7 +32,7 @@ from dogpile.cache.util import memoized_
 from pyramid.settings import asbool
 
 from vcsserver.lib.memory_lru_dict import LRUDict, LRUDictDebug
-from vcsserver.utils import safe_str
+from vcsserver.utils import safe_str, safe_unicode
 
 
 _default_max_size = 1024
@@ -133,7 +133,7 @@ class FileNamespaceBackend(PickleSeriali
         try:
             super(FileNamespaceBackend, self).__init__(arguments)
         except Exception:
-            log.error('Failed to initialize db at: %s', db_file)
+            log.exception('Failed to initialize db at: %s', db_file)
             raise
 
     def __repr__(self):
@@ -265,7 +265,7 @@ class BaseRedisBackend(redis_backend.Red
 
     def get_mutex(self, key):
         if self.distributed_lock:
-            lock_key = redis_backend.u('_lock_{0}').format(safe_str(key))
+            lock_key = redis_backend.u(u'_lock_{0}'.format(safe_unicode(key)))
             return get_mutex_lock(self.client, lock_key, self._lock_timeout,
                                   auto_renewal=self._lock_auto_renewal)
         else: