Add Static labels

[burningalchemist]

Hi @free ,

It seems like the previous pull request was abandoned, though the idea is good.
I checked your previous comments and added what was missing.

What's your opinion?

[free]

I'd rather use a map[string]string, similar to StaticConfig.Labels. Then you won't run into any issues due to duplicate labels, as the YAML parser will simply take the last value. As is, you'll likely get a cryptic start-up error when creating the metric family.

[burningalchemist]

It also looks better to me, but I thought it was already agreed. Will change.

[free]

Also, these are no (result set) columns, they're simply static constants. The comment should be something like "constant/fixed label-value pairs".

[burningalchemist]

I thought that the implementation it was more or less agreed, so I picked the initial contributor commit as is and added the missing bit. :) I'll work this out. 👍

[free]

Thanks for putting up with me.

Apparently I didn't look too close at the original PR. I'm not a Go programmer by day, the only reason I wrote this in Go is that Prometheus is written in Go and some of the underlying libraries could be reused.

[burningalchemist]

Just based upon the number of docker image pulls (~1.4m) you did a really good job, thanks for that! I recently joined the team and sql_exporter is used there across many environments. The best thing I can do personally is to contribute to the upstream. :)

[free]

Well, I tried. I would have used anything that was already there, but couldn't find anything half-decent for MSSQL, so I had to roll my own. Plus I needed to be able to run arbitrary queries.

[burningalchemist]

👍

[free]

This will append the slice to itself, it doesn't change anything. It should instead be:

Suggested change

	sortableLabels := append(constLabels[:0:0], constLabels...)
	sortedLabels := append([]int(nil), constLabels...)

See https://play.golang.org/p/c-_2YcYxi5p

[burningalchemist]

Yeah, it makes sense. I just came across the suggestion here and I like the guarantees we have with that, so decided to try something new and also get your opinion about it.

It gives me the same result if I'm not missing anything: https://play.golang.org/p/rs0LoTAI8xY

[free]

You're right, of course, please leave it as is. My apologies.

I did try your code in the playground, but I must have appended the value directly to the [:0:0] slice instead of appending the contents of the slice itself first.

[burningalchemist]

No worries, thanks for double checking!

[free]

Suggested change

	// Create a copy of original slice to apply sort properly
	// Create a copy of original slice to avoid modifying constLabels

[burningalchemist]

👍

[burningalchemist]

@free I've applied the changes you suggested, now it works exactly as we discussed:
For the configuration below:

  - metric_name: test-query
    type: gauge
    help: 'Time when prices for a market were last updated'
    key_labels:
    - test
    static_labels:
      testkey: testvalue
      testkey2: testvalue2
      testkey2: testvalue2  // accidental duplicate
    values: [id]
    query: |
      SELECT *
      FROM "doc"."test";

we get the following result (database values are correct):

# HELP test-query Time when prices for a market were last updated
# TYPE test-query gauge
test-query{test="2",testkey="testvalue",testkey2="testvalue2"} 1

[free]

LGTM, thanks.