Fix and document counter types

Document each counter type available and fixes the various counter already
implemented.

This fixes bug #1023969.

Change-Id: Ibc8b726d59c3f9433109096958b1d40db043e70d
Signed-off-by: Julien Danjou <julien@danjou.info>

ceilometer/compute/libvirt.py

@@ -120,7 +120,7 @@ class CPUPollster(plugin.PollsterBase):
                                                  )
                 yield make_counter_from_instance(instance,
                                                  name='instance',
-                                                 type='delta',
+                                                 type='cumulative',
                                                  volume=1,
                                                  )
             except Exception as err:

ceilometer/compute/network.py

@@ -39,7 +39,7 @@ class FloatingIPPollster(plugin.PollsterBase):
                 yield counter.Counter(
                     source='?',
                     name='floating_ip',
-                    type='delta',
+                    type='cumulative',
                     volume=1,
                     user_id=None,
                     project_id=ip.project_id,

ceilometer/compute/notifications.py

@@ -39,7 +39,7 @@ class InstanceNotifications(plugin.NotificationBase):
         return [counter.Counter(
             source='?',
             name='instance',
-            type='delta',
+            type='cumulative',
             volume=1,
             user_id=message['payload']['user_id'],
             project_id=message['payload']['tenant_id'],

ceilometer/counter.py

@@ -24,7 +24,22 @@ in by the plugins that create them.
 
 import collections
 
-
+# Fields explanation:
+#
+# Source:
+# Name: the name of the counter, must be unique
+# Type: the type of the counter, must be either:
+#       - cumulative: the value is incremented and never reset to 0
+#       - delta: the value is reset to 0 each time it is sent
+#       - absolute: the value is an absolute value and is not a counter
+# Volume: the counter value
+# User ID: the user ID
+# Project ID: the project ID
+# Resource ID: the resource ID
+# Timestamp: when the counter has been read
+# Duration: duration in seconds determining how long the value is valid.
+#           adding this to timestamp give the end time of the counter
+# Resource metadata: various metadata
 Counter = collections.namedtuple('Counter',
                                  ' '.join(['source',
                                            'name',

doc/source/contributing/plugins.rst

@@ -64,7 +64,7 @@ from libvirt and send back two ``Counter`` objects.  The first one, named
 "cpu", is of type "cumulative", meaning that between two polls, its value is
 not reset, or in other word that the cpu value is always provided as a duration
 that continuously increases since the creation of the instance. The second one,
-named "instance", is of type "delta", meaning that it's value is just the
+named "instance", is of type "cumulative", meaning that it's value is just the
 volume since the last poll. Here, the instance counter is only used as a way
 to tell the system that the instance is still running, hence the hard coded
 value of 1.

tests/compute/test_notifications.py

@@ -172,7 +172,7 @@ def test_process_notification():
 
     for name, actual, expected in [
         ('counter_name', info.name, 'instance'),
-        ('counter_type', info.type, 'delta'),
+        ('counter_type', info.type, 'cumulative'),
         ('counter_volume', info.volume, 1),
         ('timestamp', info.timestamp,
          INSTANCE_CREATE_END['timestamp']),