arenaskl: add BenchmarkCockroachKeysSeekPrefixGE

Add a new microbenchmark that benchmarks SeekPrefixGE but with Cockroach keys
and the Cockroach comparator.

Author: jbowens

internal/arenaskl/skl_bench_test.go

@@ -0,0 +1,65 @@
+// Copyright 2025 The LevelDB-Go and Pebble Authors. All rights reserved. Use
+// of this source code is governed by a BSD-style license that can be found in
+// the LICENSE file.
+
+package arenaskl_test
+
+import (
+	"fmt"
+	"math/rand/v2"
+	"testing"
+	"time"
+
+	"github.com/cockroachdb/pebble/cockroachkvs"
+	"github.com/cockroachdb/pebble/internal/arenaskl"
+	"github.com/cockroachdb/pebble/internal/base"
+)
+
+// BenchmarkCockroachKeysSeekPrefixGE looks at the performance of repeated calls
+// to SeekPrefixGE, with different skip distances and different settings of
+// trySeekUsingNext.
+func BenchmarkCockroachKeysSeekPrefixGE(b *testing.B) {
+	l := arenaskl.NewSkiplist(arenaskl.NewArena(make([]byte, 64<<20)), cockroachkvs.Compare)
+	rng := rand.New(rand.NewPCG(0, uint64(10000)))
+	keys, vals := cockroachkvs.RandomKVs(rng, 1000000, cockroachkvs.KeyGenConfig{
+		PrefixAlphabetLen: 26,
+		PrefixLenShared:   4,
+		RoachKeyLen:       16,
+		AvgKeysPerPrefix:  2,
+		BaseWallTime:      uint64(time.Now().UnixNano()),
+	}, 8 /* value len */)
+	prefixes := make([][]byte, len(keys))
+	for i := range prefixes {
+		prefixes[i] = keys[i][:cockroachkvs.Split(keys[i])]
+	}
+
+	var count int
+	for count = 0; ; count++ {
+		if err := l.Add(base.InternalKey{UserKey: keys[count]}, vals[count]); err == arenaskl.ErrArenaFull {
+			break
+		}
+	}
+
+	for _, skip := range []int{1, 2, 4, 8, 16} {
+		for _, useNext := range []bool{false, true} {
+			b.Run(fmt.Sprintf("skip=%d/use-next=%t", skip, useNext), func(b *testing.B) {
+				it := l.NewIter(nil, nil)
+				j := 0
+				b.ResetTimer()
+				it.SeekPrefixGE(prefixes[j], keys[j], base.SeekGEFlagsNone)
+				for i := 1; i < b.N; i++ {
+					j += skip
+					var flags base.SeekGEFlags
+					if useNext {
+						flags = flags.EnableTrySeekUsingNext()
+					}
+					if j >= count {
+						j = 0
+						flags = flags.DisableTrySeekUsingNext()
+					}
+					it.SeekPrefixGE(prefixes[j], keys[j], flags)
+				}
+			})
+		}
+	}
+}