[openstack-dev] [ceilometer] Counter frequency bp discussion

Doug Hellmann doug.hellmann at dreamhost.com
Mon Jan 7 17:40:27 UTC 2013

On Sat, Jan 5, 2013 at 8:03 AM, Jiang, Yunhong <yunhong.jiang at intel.com>wrote:

> Hi, Doug
>         As a follow--up with you on the counter frequency discussion, I
> create a wiki page at
> http://wiki.openstack.org/Ceilometer/blueprints/publisher-counters-frequency. Please have a look on it.

This feels a little more complicated than should be necessary to meet the
requirements we have.

First, lets constrain each pipeline to go to a single publisher. The
transformers have mostly been described as publisher-specific anyway
(formatting the data in a particular way, for example), so I think in
practice we are likely to only have one publisher per pipeline anyway. If
this proves to be wrong, we can change it later to allow more than one
publisher, but starting with one will give us an easier target to hit now.

Second, the interval should be a property of the pipeline rather than a
transformer or counter. There are two reasons for that change: (1) each
pipeline must have an interval, but if we leave it up to the transformer a
user may configure a pipeline without that type of transformer in place and
(2) all of the data flowing through the pipeline (the counters) should be
collected at the same interval to give the pipeline a simple operating
model for the user to understand it ("every N seconds this pipeline
collects data from these sources and publishes it to this destination").

If we make those changes, then we only need to schedule timers for each
unique interval value. When a timer goes off, data for the counters for all
of the pipelines with that interval can be collected and sent into the
appropriate pipelines. We can do some caching to avoid collecting the same
data over and over if multiple pipelines want the same counters, but that's
an optimization we can make after we have the basic logic working correctly.

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