Speed up widget generation

[kbrock]

Reporting is bringing back all rows to check for data types.
For widgets, this was bringing back unnecessary data.

The change detects if the input is a query, and uses ActiveRecord::Relation#klass instead of fetching all rows and comparing them.

https://bugzilla.redhat.com/show_bug.cgi?id=1251259

ms	bytes	objects	queries	query (ms)	rows	comments
5,962.8	51,785,052*	6,412,174	1,196	1,570.6	6,768	before.4
260.9	6,975,857	84,669	56	105.8	16	after.4
95.6%	>87%	99%	95%	93.3%	99.8%	diff

EOM

---

The verbose numbers section.
If you note, the numbers below were used up top

w = MiqWidget.find_by(name: 'report_top_storage_consumers') ; opts = w.group_options.last
bookend("generate", gc: true) { w.send(:content_generator).generate(w, *opts) }

ms	bytes	objects	queries	query (ms)	rows	comments
8,048.9	117,580,084*	9,798,996	1,196	2,507.0	6,768	before.1
5,948.2	96,799,316*	6,407,554	1,196	1,463.2	6,768	before.2
5,994.2	51,616,590*	6,412,285	1,196	1,491.9	6,768	before.3
5,962.8	51,785,052*	6,412,174	1,196	1,570.6	6,768	before.4
1,314.7	46,933,349*	1,091,083	56	169.7	16	after.1
249.0	6,975,855	84,669	56	96.5	16	after.2
265.0	6,975,856	84,669	56	101.7	16	after.3
260.9	6,975,857	84,669	56	105.8	16	after.4

* Memory usage does not reflect 3,599,936 freed objects - before.1
* Memory usage does not reflect 2,200,252 freed objects - before.2
* Memory usage does not reflect 2,204,985 freed objects - before.3
* Memory usage does not reflect 2,204,873 freed objects - before.4
* Memory usage does not reflect 9,060 freed objects - after.1

[miq-bot]

Checked commit kbrock@9dab1c4 with ruby 2.2.6, rubocop 0.47.1, and haml-lint 0.20.0
1 file checked, 1 offense detected

app/models/metric/helper.rb

• ❗ - Line 126, Col 18 - Style/TrailingWhitespace - Trailing whitespace detected.

[isimluk]

👍

[gtanzillo]

Nice improvement 👍

[kbrock]

@chessbyte @gtanzillo you ok marking this as darga/yes?
The BZ is from 5.4

Should be minimal risk (thought I'm unsure why we have to check every record that it is a Metric record vs just the first - not sure the history there)

[kbrock]

WARNING: these numbers are not right

[simaishi]

Euwe backport details:

$ git log -1
commit 58cbec8d9ef464d1b0adf11afe47339dd11b244c
Author: Gregg Tanzillo <gtanzill@redhat.com>
Date:   Wed Mar 8 08:56:49 2017 -0500

    Merge pull request #14224 from kbrock/widget_1
    
    Speed up widget generation
    (cherry picked from commit 15f7ba471e1a31a482a76168b6a07a19b2cf9917)
    
    https://bugzilla.redhat.com/show_bug.cgi?id=1434150