kv/concurrency: compute contention event duration from (key,txn) wait start time

[nvanbenschoten]

Fixes #98104.

This commit resolves the bug identified in #98104 where multiple contention events could be emitted with overlapping durations, such that when these durations were added together (e.g. by GetCumulativeContentionTime), their sum was larger than the runtime of the entire query. This was possible because as of 70ef641, we were failing to reset the waiting start time on each new lock holder transaction for the same key.

This commit fixes this by computing the contention event duration using contentionTag.waitStart instead of waitingState.lockWaitStart. It also cleans up some of this code and makes it harder to make such a mistake in the future.

Release note: None

[cockroach-teamcity]

This change is 

[andreimatei]

Reviewable status: complete! 0 of 0 LGTMs obtained (waiting on @AlexTalks and @nvanbenschoten)

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pkg/kv/kvserver/concurrency/lock_table_waiter_test.go line 953 at r1 (raw file):

	var events []*kvpb.ContentionEvent

	h := newContentionEventTracer(sp, clock)

wanna take the opportunity to make this take an hlc.WallClock instead of *hlc.Clock ?

[andreimatei]

Reviewable status: complete! 1 of 0 LGTMs obtained (waiting on @AlexTalks and @nvanbenschoten)

[nvanbenschoten]

TFTR!

bors r=andreimatei

Reviewable status: complete! 1 of 0 LGTMs obtained (waiting on @AlexTalks and @andreimatei)

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pkg/kv/kvserver/concurrency/lock_table_waiter_test.go line 953 at r1 (raw file):

Previously, andreimatei (Andrei Matei) wrote…

wanna take the opportunity to make this take an hlc.WallClock instead of *hlc.Clock ?

+1 on the idea, but I need to backport this all the way to release-22.1 and I suspect that such a refactor will make that more difficult, so I'll save it for another PR.

[craig]

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[nvanbenschoten]

bors r=andreimatei

[craig]

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error creating merge commit from 1201c01 to blathers/backport-release-22.1-99166: POST https://api.github.com/repos/cockroachdb/cockroach/merges: 409 Merge conflict []

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