kv: relax bounds for YCSB splits tests

We've seen variants of YCSB A and B fail with both higher and
lower number of splits. In response, we've changed the bounds of both
these variants independently. The commentary suggests the number of
splits here should be the same for both variants; this patch makes it
such, picking the max upper bound and min lower bound across the two
variants.

Closes #155951

Release note: None

Author: arulajmani

pkg/cmd/roachtest/tests/split.go

@@ -335,9 +335,9 @@ func registerLoadSplits(r registry.Registry) {
 				maxSize:      10 << 30,               // 10 GB
 				cpuThreshold: 100 * time.Millisecond, // 1/10th of a CPU per second.
 				// YCSB/A has a zipfian distribution with 50% inserts and 50% updates.
-				// The number of splits should be between 15-38 after 10 minutes with
+				// The number of splits should be between 13-38 after 10 minutes with
 				// 100ms threshold on 8vCPU machines.
-				minimumRanges:     17,
+				minimumRanges:     15,
 				maximumRanges:     40,
 				initialRangeCount: 2,
 				load: ycsbSplitLoad{
@@ -362,7 +362,7 @@ func registerLoadSplits(r registry.Registry) {
 				// The number of splits should be similar to YCSB/A.
 				cpuThreshold:      100 * time.Millisecond, // 1/10th of a CPU per second.
 				minimumRanges:     15,
-				maximumRanges:     35,
+				maximumRanges:     40,
 				initialRangeCount: 2,
 				load: ycsbSplitLoad{
 					workload:     "b",