Add option to client_golang to *not* send the time on a Series() call

[jacksontj]

The series call doesn't require a time, it would be nice if we had some mechanism in the go API to not set a time. I had opened #615 towards this, but I'm not sure this is a great approach, maybe we instead make the time.Time pointers?

[beorn7]

Could the zero value of time.Time be used as a marker for “do not use”? (Cf. https://golang.org/pkg/time/#Time.IsZero .) I might be completely wrong. Not an expert of the API client. @krasi-georgiev to vet.

[jacksontj]

My only concern is that prom's minTime is actually significantly before time.Time{}

minTime = -292273086-05-16 16:47:06 +0000 UTC
time.Time{} = 0001-01-01 00:00:00 +0000 UTC

on go playground

So if you wanted to query a time before Zero time (since apparently thats valid?) it'd be a bit weird to have our "null" (don't send a value) be in the middle of that.

[beorn7]

Oh right, I now even remember that we had discussed this problem in a different context already (i.e. a valid Prometheus sample might happen to have the time.Time zero value as its actual timestamp).

[beorn7]

So yeah, disregard my comment, please.

[bboreham]

I just hit this on LabelValues(). Evidently somebody else though that time.Time{} should behave as 'not set':

https://github.com/cortexproject/cortex/blob/07d6cfc4eb848fc410262773255dfec750c0a64f/integration/getting_started_single_process_config_test.go#L62

How about creating a constant with a value of minTime, that would be taken as "don't send a value"?

[jacksontj]

Its been a while since this issue was touched last; but this came up again as an issue on promxy (jacksontj/promxy#528) -- I was wondering if we had any ideas/thoughts on fixing this?

[jacksontj]

The "clearest" API change (IMO) would be to change from a time.Time to a *time.Time (pointer) -- that way if it is null we just don't send it on. This is more accurate to what the underlying HTTP API is (since these are optional arguments).

[jacksontj]

I was looking to create a PR against this and noticed that the client already is VERY inconsistent. Some methods (such as Query) use IsZero and others do nothing. From a quick review of the prometheus server API -- all of the time values are optional (except for QueryRange) -- so it this seems like something we should definitely fix.

Practically speaking time.Time{} or *time.Time approaches both work (*time.Time is more accurate, but an API change).

[bboreham]

Pointers to Time here is not idiomatic Go, in my opinion.

Adding a new method like SeriesForAllTime would be non-breaking.

I think I’d be fine with the zero time meaning “not set”, since that is obvious. I doubt there are many people who have data at that instant.

(Note there is a bug with model.Earliest - #951)