prometheus: Optimize metrics formatting

It is faster to use join for join multiple strings than the regular
string concatenation since it does not create a new string on each
iteration.

Signed-off-by: Boris Ranto <branto@redhat.com>
(cherry picked from commit d395868d9ef787d98fa1a0f9dd0e84e41d04fd26)

diff --git a/src/pybind/mgr/prometheus/module.py b/src/pybind/mgr/prometheus/module.py
index 121db40e79d8e9c8b6321969deef9cd5a3814d9c..38f04e8480400bbef498ad6131b5905570af670c 100644 (file)
--- a/src/pybind/mgr/prometheus/module.py
+++ b/src/pybind/mgr/prometheus/module.py
@@ -602,7 +602,6 @@ class Module(MgrModule):
                     ))
                     self.metrics.set(path, value, (daemon,))
 
-
         return self.metrics.all()
 
     def get_file_sd_config(self):
@@ -662,10 +661,8 @@ class Module(MgrModule):
                 return self
 
             def format_metrics(self, metrics):
-                formatted = ''
-                for m in metrics.values():
-                    formatted += m.str_expfmt()
-                return formatted + '\n'
+                _metrics = [m.str_expfmt() for m in metrics.values()]
+                return ''.join(_metrics) + '\n'
 
             @cherrypy.expose
             def index(self):