Drop the metric name after any transformation

[juliusv]

Prometheus has no way of telling whether the original name of a metric is still semantically correct after applying any kind of transformation to it, so the metric name should be dropped in that case.

This requires some refactoring, as we currently don't deal well with metrics without a name everywhere (in one place, we even panic).

[juliusv]

@brian-brazil I'd like to get your opinion on this: I'm actually working on a change which tries to be clever about assigning automatic new metric names after transformations, when possible. Some examples:

sum(http_request_duration_microseconds) by (job, instance)`
  =>
`job_instance:http_request_duration_microseconds:sum{instance="http://localhost:9090/metrics",job="prometheus"}`

// What about this case? You said using only one colon in a name is ugly.
// Would we want to invent some "global" aggregation level name if no by-clause is given?
sum(http_request_duration_microseconds)
  =>
http_request_duration_microseconds:sum{}

// Not implemented yet, but possible. Same problem about having only one colon:
rate(http_request_duration_microseconds[5m])
  =>
http_request_duration_microseconds:rate5m{...}

// Any binops still end up erasing the metric name, as they probably change the original meaning.
http_request_duration_microseconds / 10
  =>
{}

If the corner-cases and combinations of multiple aggregations end up generating too ugly metric names, we can still decide for just always dropping the metric names after any transformations. Just wanted to throw this idea out there.

[juliusv]

/cc @u-c-l

[brian-brazil]

I think this may be workable, and avoid a lot of problems if we can pull it off. I suspect there's too many edge cases though.

For example the purpose of the level: prefix is so you can tell what labels are on a variable, a form of Hungarian notation that makes it obvious if you've messed up your label modifiers. That doesn't work when a label being empty is the same as it not existing, and I don't think it's practical to add in the strong typing needed to make it work.

[juliusv]

For now, this is solved by completely dropping the metric name in f3e9f6b. This has yet to be merged into master after merging the exp/storage-ng branch. Keeping this issue open until then to not lose track of this.

[beorn7]

Merged. I'm going to close this. Please reopen if needed.

[lock]

This thread has been automatically locked since there has not been any recent activity after it was closed. Please open a new issue for related bugs.