There are a lot of things that I dislike about IMetric. It provides too much
flexibility and at the same time not enough information/conventions to be able
to interpret the numbers it returns correctly. We recently had a case where
someone was trying to compute an average using a ReducedMetric and a
MeanReducer (which by the way should be deprecated because it is fundamentally
flawed). This hands the metric collector an average. How is it supposed to
combine one average with another when doing a roll up, either across components
or across time ranges? It just does not work mathematically unless you know
that all of the averages had the exact same number of operations in them, which
we cannot know.
This is why dropwizard and other metrics systems have a specific set up
supported metrics, not object, that they know mathematically work out. A gauge
is different from a counter, which is different from a ratio, or a meter, or a
timer, or a histogram. Please lets not reinvent the wheel here, we already did
it wrong once, lets not do it wrong again. We are using dropwizard in other
places in the code internally, I would prefer that we standardize on it, or a
thin wrapper around it based on the same concepts. Or if there is a different
API that someone here would prefer that we use that is fine with me too. But
lets not write it ourselves, lets take from the experts who have spent a long
time building something that works.
- Bobby
On Tuesday, May 17, 2016 10:10 PM, Jungtaek Lim <[email protected]> wrote:
Hi devs,
Since IMetric#getValueAndReset doesn't restrict return type, it gives us
flexibility but metrics consumer should parse the value without context
(having just some assumptions).
I've look into some open source metrics consumers, and many of them support
Number, Map<String, Number/String>, and one of them supports Nested Map.
For the case of Map its key is appended to metric key and value is
converted to 'double'. I think it would be enough, but I'm not sure we can
rely on all metrics consumers to handle properly, too.
I feel if we can recommend proper types of DataPoint value for storing
metrics to time-series DB via metrics consumer it would be great. It can be
used to protocol between IMetric users and metrics consumer developers.
What do you think?
Thanks,
Jungtaek Lim (HeartSaVioR)
ps. I'm not heavy user of time-series DBs (I researched some, but they
don't document type/size of value clearly) so if someone could give the
information of supporting type/size of value of time-series DBs it should
be great for me. Or we can just assume number as 'double' as above and go
forward.
