remove count(*) from MiqQueue.get

[kbrock]

For MiqQuery.get, we perform an unneeded COUNT(*), which is almost as expensive as the SELECT *

This PR removes that

ms	bytes	objects	queries	query (ms)	rows	comments
2,019.3	31,802,410	365,569	612	1,450.0	1,020	before-4
1,633.1	28,129,576	323,341	510	1,130.4	1,020	after-2
19.1%	12%	12%	17%	23%	0	diff

---

TMI

100.times { MiqQueue.put(:class_name  => 'MyClass', :method_name => 'method1', :args => [1, 2]) }
bookend("miq_queue.count") { 102.times { MiqQueue.get } }

I highlighted the count(*) which is present in before but not after

ms	query	query ms	rows	comments
2,114.9	612	1,528.6	1,020	count#before-2
520.7	102	520.7		.SELECT COUNT(count_column)
511.2	102	482.3	1,020	.SELECT "miq_queue".*
108.0	102	97.7		.SELECT "miq_workers".*
48.7	102	48.7		.BEGIN
253.4	102	253.4		.UPDATE "miq_queue" SET "state" = 'dequeue', "handler_id" = 10000000000018, "handler_type" = 'MiqServer', "updated_on" = .{28}, "lock_version" = 1
86.6	102	86.6		.COMMIT

It is nice that overall, the query numbers are pretty consistent

ms	bytes	objects	queries	query (ms)	rows	comments
1,949.5	31,802,462	365,569	612	1,365.4	1,020	before-1
2,114.9	31,802,328	365,569	612	1,528.6	1,020	before-2
2,162.4	31,802,438	365,569	612	1,580.1	1,020	before-3
2,019.3	31,802,410	365,569	612	1,450.0	1,020	before-4

ms	bytes	objects	queries	query (ms)	rows	comments
1,608.7	28,129,620	323,341	510	1,106.5	1,020	after-1
1,633.1	28,129,576	323,341	510	1,130.4	1,020	after-2
1,655.4	28,129,582	323,341	510	1,151.2	1,020	after-3
1,511.1	28,129,690	323,341	510	1,018.5	1,020	after-4

[isimluk]

👍

take it to the limit!

[isimluk]

@kbrock while this avoids the count, we can make it even more 🍨-y

I suggest we keep limit there and remove the line (return nil if msgs.empty?). Here is why:

The difference between take and limit is that take returns array, limit returns relation. When we call
msgs.empty? -> We either

• run empty? on relation that runs count on that relation
• or we run empty? on array

You changed the relation to the array, so we don't run the count. However (!) we don't need that empty? at all!!! See the code bellow. The empty? call is trying to be smarty, but it optimizes nothing really. See the code below the empty?.

So, I suggest, we just remove

return nil if msgs.empty? # Nothing available in the queue

and we are done.

[kbrock]

@isimluk great suggestion.

[isimluk]

@kbrock could you please clean this one? I think it is new:

❗️ - Line 178, Col 8 - Style/TrailingWhitespace - Trailing whitespace detected.

[miq-bot]

This pull request is not mergeable. Please rebase and repush.

[miq-bot]

Checked commit kbrock@eb4d55d with ruby 2.2.6, rubocop 0.47.1, and haml-lint 0.20.0
1 file checked, 0 offenses detected
Everything looks good. 🍪