Use query insead of query_range when we do not need full data.

[yaacov]

Compute > Containers > Providers - click a provider - toolbar Monitoring > Ad Hoc Metrics

Description

The ad hoc page use a the same query from Prometheus to get data and to get only labels.
We query labels for all the metrics in the system, this query may take a lot of time (e.g. more then 10s) on large system scales.

This PR changes the query we use when we only want labels. Now we use the less stressful query instead of query_range, when we do not need to get data.

More info

On my small system this reduced query time from 900ms to 600ms, on bigger systems this can change from several s' to the ms' range.

BZ: https://bugzilla.redhat.com/show_bug.cgi?id=1511402

Screenshots
Before, query takes ~900ms on my very small system:

After, query takes ~600ms on my very small system:

[yaacov]

@miq-bot add_label bug, compute/containers, gaprindashvili/yes

@simon3z @moolitayer @zeari @himdel @martinpovolny please review

https://bugzilla.redhat.com/show_bug.cgi?id=1511402 target: 5.9.0

[yaacov]

@joelddiaz @ilackarms , this may have impact on the OPS effort, PTAL

[miq-bot]

Checked commit yaacov@510fc86 with ruby 2.3.3, rubocop 0.47.1, haml-lint 0.20.0, and yamllint 1.10.0
1 file checked, 0 offenses detected
Everything looks fine. 🏆

[joelddiaz]

👍 this should definitely help with the timeouts we were seeing last week

[yaacov]

@ilackarms can you make an image with this, so @joelddiaz can test it in the wild and compare with an image without this fix ?

[himdel]

Code looks good, has anyone tested this?

(EngLab-prometheus gives me execution expired now)

[yaacov]

Checking EngLab-prometheus ... a moment :-)

[yaacov]

@himdel sorry about that, machines are up now.

[himdel]

Perfect, thanks! :)

LGTM, I'm getting the same set of tags :).

[himdel]

@yaacov Just a note here though... on my dev setup, this makes the time go from about 5.89 seconds on master to about 6.12s with this PR.

(But not sure if this is statistically significant or anything, just not seeing that huge performance gain ;).)

[yaacov]

@himdel I have a small setup, on @joelddiaz machine this made a big improvement, but we only tested this query vs query_range, once on a "real" machine.

[simaishi]

Gaprindashvili backport details:

$ git log -1
commit 9f48355bb427410b4a1110c61f8685bd87f4e34b
Author: Martin Hradil <himdel@seznam.cz>
Date:   Thu Nov 16 13:24:15 2017 +0000

    Merge pull request #2736 from yaacov/use-query-instead-of-query_range-to-get-metrics-tags
    
    Use query insead of query_range when we do not need full data.
    (cherry picked from commit 6b6a87e522f4c2bb348e2f8fbd46e6e9984252e3)
    
    https://bugzilla.redhat.com/show_bug.cgi?id=1514523