storage: use RangeKeyChanged() in MVCCClearTimeRange

[erikgrinaker]

Some minor optimizations that might yield minor performance
improvements. We don't have any benchmarks for this function, and it's
used fairly rarely.

Release justification: bug fixes and low-risk updates to new functionality

Release note: None

[cockroach-teamcity]

This change is 

[tbg]

Reviewed 4 of 5 files at r3, 1 of 1 files at r4, all commit messages.
Reviewable status: complete! 0 of 0 LGTMs obtained (waiting on @erikgrinaker)

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-- commits line 70 at r4:
Also seems like low-reward, should we let this sit then?

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pkg/storage/mvcc.go line 2697 at r4 (raw file):

					!clearedMeta.Timestamp.ToTimestamp().LessEq(v.Timestamp) {
					rangeKeys := iter.RangeKeysIgnoringTime()
					if rangeKeys.IsEmpty() || !rangeKeys.HasBetween(k.Timestamp, v.Timestamp.Prev()) {

This is just making the previous behavior more explicit, right? Since IsEmpty() => !HasBetween.

[erikgrinaker]

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

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-- commits line 70 at r4:

Previously, tbg (Tobias Grieger) wrote…

Also seems like low-reward, should we let this sit then?

I'd rather get everything ported to RangeKeyChanged(), so that's the canonical way to handle this. Also, this should have a decent boost when there are MVCC range tombstones present, since it avoids both a key comparison and binary search in the hot path.

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pkg/storage/mvcc.go line 2697 at r4 (raw file):

Previously, tbg (Tobias Grieger) wrote…

This is just making the previous behavior more explicit, right? Since IsEmpty() => !HasBetween.

It's really a performance optimization, since HasBetween calls through to sort.Search, which was found to be really expensive over in #86515. Even though that PR now checks the empty case internally, omitting the function call entirely was found to have a non-negligible perf benefit in very hot paths like ComputeStats so may as well check it here too.

[erikgrinaker]

bors r=tbg

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