Description of problem:

Customer has configured the overcloud ceilometer services to perform hardware polling via SNMP of the overcloud compute nodes. They have a requirement to have SNMP hardware data queryable by gnocchi API. They've configured an arithmetic transformer to gather this data, but its consistently dropping samples. We noticed a method in arithmetic.py that seems to be missing returning a sample. We've added this and the samples are no longer being dropped and are appearing in gnocchi measures show.


Version-Release number of selected component (if applicable):

OSP10

openstack-ceilometer-api-7.1.1-6.el7ost.noarch
openstack-ceilometer-central-7.1.1-6.el7ost.noarch
openstack-ceilometer-collector-7.1.1-6.el7ost.noarch
openstack-ceilometer-common-7.1.1-6.el7ost.noarch
openstack-ceilometer-compute-7.1.1-6.el7ost.noarch
openstack-ceilometer-notification-7.1.1-6.el7ost.noarch
openstack-ceilometer-polling-7.1.1-6.el7ost.noarch
puppet-ceilometer-9.5.0-4.el7ost.noarch
python-ceilometer-7.1.1-6.el7ost.noarch
python-ceilometerclient-2.6.2-1.el7ost.noarch
python-ceilometermiddleware-0.5.2-1.el7ost.noarch

How reproducible:

Every time.

Steps to Reproduce:
1. Deploy OSP10 and setup SNMP hardware polling with new sinks and transforms (details in below comment).
2. Observe in ceilometer agent-notification.log that samples of this transformer are always being dropped.

Actual results:

Samples with arithmetic transformer are consistently being dropped.

Expected results:

Samples with arithmetic transformer should not be dropped, and passed onto storage into gnocchi.


Additional info:

We've seemed to alleviate the sample dropping issue with the following code change:

~~~
  - /usr/lib/python2.7/site-packages/ceilometer/pipeline.py
  
    443 class SampleSink(Sink):
    444 
    445     NAMESPACE = 'ceilometer.publisher'
    446 
    447     def _transform_sample(self, start, sample):
    448         try:
    449             for transformer in self.transformers[start:]:
    450                 sample = transformer.handle_sample(sample)              <=== Expects return of sample.
    451                 if not sample:
    452                     LOG.debug(
    453                         "Pipeline %(pipeline)s: Sample dropped by "
    454                         "transformer %(trans)s", {'pipeline': self,
    455                                                   'trans': transformer})
    456                     return
    457             return sample

  - /usr/lib/python2.7/site-packages/ceilometer/transformer/arithmetic.py
  
     99     def handle_sample(self, _sample):                                    <==== Not returning any value.
    100         self._update_cache(_sample)
    101         self.latest_timestamp = _sample.timestamp
    102
~~~

with the code change: (No drops)

~~~
    def handle_sample(self, _sample):
        self._update_cache(_sample)
        self.latest_timestamp = _sample.timestamp
        return _sample                                                           <====  change
~~~