9:07 a.m.
Hi,
Earlier today I created HWKMETRICS-54, but I later thought about it a bit more and to me
it looks like we're not sure what the tags should really do and how the system should
be used. Lets assume the following scenario:
3 machines, each one running an agent that provides data for memory.free, memory.cached,
cpu.idle, cpu.user, cpu.system, disk.free, disk.used
Now what user might want to do in these cases is:
a) I want to get all the statistics affecting the host 1
b) I want to get all the memory.free statistics from each host
Think about the data modeling in our current hawkular-metrics for a moment. The user
starts:
I. Model everything with machine1.memory.free, machine2.memory.free etc
a) How to query machine1.* ? Can't be done. c) How to get *.memory.free? Can't be
done.
How would the query succeed with our current format? By creating tags for every occasion
on metric creation:
create machine1.memory.free (tags: machine='machine1', category='memory')
create machine2.memory.free (tags: machine='machine2', category='memory')
What the user finds out is that "why on earth do I have the metricId at all" ?
It's a good question. In our current structure we should remove metricId and just
invent something random for better Cassandra partitioning.
What it probably should look like (and this is how I assumed it was to be done until I
checked the unit tests and find out that there's nothing pointing to this OpenTSDB
familiar method):
II. memory.free, cpu.idle are the metricIds and I'll define it has a parameter
'machine'. When pushing a metric I set a tag with a value, such as
machine='machine2'.
Now when I fetch the metric "memory.free", I can get all the memory.free valuess
with 'machine'-tag indicating which machine it was gathered from. If I need to
search for all machine-statistics, then I could use the tag-searching. If I wanted only
machine1 memory.free, I would add a filter: tag machine='machine1'.
Or how are we supposed to model real-world-use-cases? The current model is quite
cumbersome and not even necessarily doable in many cases (am I supposed to query for a
metric definition before pushing any metric - because a new container could give me new
set of parameters or a new machine new set of machine parameters and I need to remember to
register them instead of pre-defined types which I might know).
- Micke