execstats: fix query level stats calculation

[yuzefovich]

execstats: fix query level contention time calculation

Previously, we were using an incorrect map to calculate the contention
time.

Release note: None

execstats: fix GetQueryLevelStats when sub- and post-queries are present

Previously, GetQueryLevelStats would incorrectly calculate the query
level stats when multiple FlowMetadata objects are passed in. That is
the case when either sub- or post-queries are present. As a result, we
would return the query level stats only for the last FlowMetadata
object. This is now fixed by aggregating the query level stats of all
FlowMetadata objects.

However, the test is missing since I don't yet see how to do it. It is
left as a TODO.

Additionally, this commit does some cleanup - using "Flows" instead of
"Flow" for metadata to indicate that multiple flows (that are part of
the same physical plan) correspond to a single metadata object (this was
a point of confusion to me), as well as some comments wrapping.

Release note: None

[cockroach-teamcity]

This change is 

[asubiotto]

Re the testing, you could probably add a public testing function to utils_test.go that creates a FlowMetadata from specified internal maps. You could create two simple ones (e.g. single processor stats with a dummy kv time) and assert that the result is what you expect.

Reviewed 2 of 2 files at r1, 3 of 6 files at r2.
Reviewable status: complete! 0 of 0 LGTMs obtained (waiting on @asubiotto and @yuzefovich)

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pkg/sql/execstats/traceanalyzer.go, line 113 at r2 (raw file):

// aggregate updates s to include stats from other.
func (s *QueryLevelStats) aggregate(other QueryLevelStats) {

If you rebase, I added an Accumulate method in a recent PR.

[yuzefovich]

Added a simple unit test. I originally thought that we need to inject the stats into the trace and didn't realize we can artificially add component stats directly into the FlowsMetadata objects.

Reviewable status: complete! 0 of 0 LGTMs obtained (waiting on @asubiotto)

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pkg/sql/execstats/traceanalyzer.go, line 113 at r2 (raw file):

Previously, asubiotto (Alfonso Subiotto Marqués) wrote…

If you rebase, I added an Accumulate method in a recent PR.

Ack.

[asubiotto]

Thanks!

Reviewed 6 of 6 files at r3, 6 of 6 files at r4.
Reviewable status: complete! 1 of 0 LGTMs obtained

[yuzefovich]

TFTR!

bors r+

[craig]

Build succeeded:

• GitHub CI (Cockroach)