perf: replace LLRB-tree with btree in interval.Tree

Fixes #6465

pkg/ccl/sqlccl/backup.go

@@ -138,7 +138,7 @@ func allRangeDescriptors(ctx context.Context, txn *client.Txn) ([]roachpb.RangeD
 // spansForAllTableIndexes returns non-overlapping spans for every index and
 // table passed in. They would normally overlap if any of them are interleaved.
 func spansForAllTableIndexes(tables []*sqlbase.TableDescriptor) []roachpb.Span {
-	sstIntervalTree := interval.Tree{Overlapper: interval.Range.OverlapExclusive}
+	sstIntervalTree := interval.Tree{Overlapper: interval.ExclusiveOverlapper}
 	for _, table := range tables {
 		for _, index := range table.AllNonDropIndexes() {
 			if err := sstIntervalTree.Insert(intervalSpan(table.IndexSpan(index.ID)), false); err != nil {

pkg/storage/command_queue.go

@@ -139,8 +139,8 @@ func (c *cmd) String() string {
 // typically contain many spans, but are spatially disjoint.
 func NewCommandQueue(coveringOptimization bool) *CommandQueue {
 	cq := &CommandQueue{
-		reads:                interval.Tree{Overlapper: interval.Range.OverlapExclusive},
-		writes:               interval.Tree{Overlapper: interval.Range.OverlapExclusive},
+		reads:                interval.NewTree(interval.ExclusiveOverlapper),
+		writes:               interval.NewTree(interval.ExclusiveOverlapper),
 		wRg:                  interval.NewRangeTree(),
 		rwRg:                 interval.NewRangeTree(),
 		coveringOptimization: coveringOptimization,

pkg/util/cache/cache.go

@@ -496,7 +496,7 @@ func (ic *IntervalCache) MakeKey(start, end []byte) IntervalKey {
 
 // Implementation of cacheStore interface.
 func (ic *IntervalCache) init() {
-	ic.tree = interval.Tree{Overlapper: interval.Range.OverlapExclusive}
+	ic.tree = interval.NewTree(interval.ExclusiveOverlapper)
 }
 
 func (ic *IntervalCache) get(key interface{}) *Entry {