tenantrate: add "test" that reports IOPS estimations

This change adds a "test" facility which takes the description of a
uniform workload (read percentage, read size, write size) and prints
out an estimation of the sustained IOPS and burst IO. This will allow
a better understanding of how changes to the settings or the mechanism
translate into IOPS changes.

Release note: None

pkg/kv/kvserver/tenantrate/helpers_test.go

@@ -24,3 +24,26 @@ func OverrideSettingsWithRateLimits(settings *cluster.Settings, rl LimitConfigs)
 	writeRateLimit.Override(&settings.SV, int64(rl.WriteBytes.Rate))
 	writeBurstLimit.Override(&settings.SV, rl.WriteBytes.Burst)
 }
+
+// DefaultLimitConfigs returns the configuration that corresponds to the default
+// setting values.
+func DefaultLimitConfigs() LimitConfigs {
+	return LimitConfigs{
+		ReadRequests: LimitConfig{
+			Rate:  Limit(readRequestRateLimit.Default()),
+			Burst: readRequestBurstLimit.Default(),
+		},
+		WriteRequests: LimitConfig{
+			Rate:  Limit(writeRequestRateLimit.Default()),
+			Burst: writeRequestBurstLimit.Default(),
+		},
+		ReadBytes: LimitConfig{
+			Rate:  Limit(readRateLimit.Default()),
+			Burst: readBurstLimit.Default(),
+		},
+		WriteBytes: LimitConfig{
+			Rate:  Limit(writeRateLimit.Default()),
+			Burst: writeBurstLimit.Default(),
+		},
+	}
+}

pkg/kv/kvserver/tenantrate/limiter_test.go

@@ -15,6 +15,7 @@ import (
 	"bytes"
 	"context"
 	"fmt"
+	"math"
 	"regexp"
 	"sort"
 	"strings"
@@ -30,6 +31,7 @@ import (
 	"github.com/cockroachdb/cockroach/pkg/util/timeutil"
 	"github.com/cockroachdb/datadriven"
 	"github.com/cockroachdb/errors"
+	"github.com/dustin/go-humanize"
 	"github.com/stretchr/testify/require"
 	"gopkg.in/yaml.v2"
 )
@@ -105,10 +107,11 @@ var testStateCommands = map[string]func(*testState, *testing.T, *datadriven.Test
 	"metrics":         (*testState).metrics,
 	"get_tenants":     (*testState).getTenants,
 	"release_tenants": (*testState).releaseTenants,
+	"estimate_iops":   (*testState).estimateIOPS,
 }
 
 func (ts *testState) run(t *testing.T, d *datadriven.TestData) string {
-	if !ts.initialized && d.Cmd != "init" {
+	if !ts.initialized && d.Cmd != "init" && d.Cmd != "estimate_iops" {
 		d.Fatalf(t, "expected init as first command, got %q", d.Cmd)
 	}
 	if f, ok := testStateCommands[d.Cmd]; ok {
@@ -486,6 +489,79 @@ func (ts *testState) releaseTenants(t *testing.T, d *datadriven.TestData) string
 	return ts.FormatTenants()
 }
 
+// estimateIOPS takes in the description of a workload and produces an estimate
+// of the IOPS for that workload (under the default settings).
+//
+// For example:
+//
+//  estimate_iops
+//  readpercentage: 50
+//  readsize: 4096
+//  writesize: 4096
+//  ----
+//  Mixed workload (50% reads; 4.0 KiB reads; 4.0 KiB writes): 256 sustained IOPS, 256 burst.
+//
+func (ts *testState) estimateIOPS(t *testing.T, d *datadriven.TestData) string {
+	var workload struct {
+		ReadPercentage int
+		ReadSize       int
+		WriteSize      int
+	}
+	if err := yaml.UnmarshalStrict([]byte(d.Input), &workload); err != nil {
+		d.Fatalf(t, "failed to parse workload information: %v", err)
+	}
+	if workload.ReadPercentage < 0 || workload.ReadPercentage > 100 {
+		d.Fatalf(t, "Invalid read percentage %d", workload.ReadPercentage)
+	}
+	limits := tenantrate.DefaultLimitConfigs()
+
+	calculateIOPS := func(readRate, readBytesRate, writeRate, writeBytesRate float64) float64 {
+		readIOPS := math.Min(readRate, readBytesRate/float64(workload.ReadSize))
+		writeIOPS := math.Min(writeRate, writeBytesRate/float64(workload.WriteSize))
+		// The reads and writes are rate-limited separately; our workload will be
+		// bottlenecked on one of them.
+		return math.Min(
+			writeIOPS*100.0/float64(100-workload.ReadPercentage),
+			readIOPS*100.0/float64(workload.ReadPercentage),
+		)
+	}
+
+	sustained := calculateIOPS(
+		float64(limits.ReadRequests.Rate), float64(limits.ReadBytes.Rate),
+		float64(limits.WriteRequests.Rate), float64(limits.WriteBytes.Rate),
+	)
+
+	burst := calculateIOPS(
+		float64(limits.ReadRequests.Burst), float64(limits.ReadBytes.Burst),
+		float64(limits.WriteRequests.Burst), float64(limits.WriteBytes.Burst),
+	)
+	fmtFloat := func(val float64) string {
+		if val < 10 {
+			return fmt.Sprintf("%.1f", val)
+		}
+		return fmt.Sprintf("%.0f", val)
+	}
+	switch workload.ReadPercentage {
+	case 0:
+		return fmt.Sprintf(
+			"Write-only workload (%s writes): %s sustained IOPS, %s burst.",
+			humanize.IBytes(uint64(workload.WriteSize)), fmtFloat(sustained), fmtFloat(burst),
+		)
+	case 100:
+		return fmt.Sprintf(
+			"Read-only workload (%s reads): %s sustained IOPS, %s burst.",
+			humanize.IBytes(uint64(workload.ReadSize)), fmtFloat(sustained), fmtFloat(burst),
+		)
+	default:
+		return fmt.Sprintf(
+			"Mixed workload (%d%% reads; %s reads; %s writes): %s sustained IOPS, %s burst.",
+			workload.ReadPercentage,
+			humanize.IBytes(uint64(workload.ReadSize)), humanize.IBytes(uint64(workload.WriteSize)),
+			fmtFloat(sustained), fmtFloat(burst),
+		)
+	}
+}
+
 func (rs *testState) FormatRunning() string {
 	var states []string
 	for _, ls := range rs.running {

pkg/kv/kvserver/tenantrate/testdata/estimate_iops

@@ -0,0 +1,49 @@
+estimate_iops
+readpercentage: 100
+readsize: 4096
+----
+Read-only workload (4.0 KiB reads): 128 sustained IOPS, 512 burst.
+
+estimate_iops
+readpercentage: 100
+readsize: 65536
+----
+Read-only workload (64 KiB reads): 16 sustained IOPS, 256 burst.
+
+estimate_iops
+readpercentage: 100
+readsize: 1048576
+----
+Read-only workload (1.0 MiB reads): 1.0 sustained IOPS, 16 burst.
+
+estimate_iops
+readpercentage: 0
+writesize: 4096
+----
+Write-only workload (4.0 KiB writes): 128 sustained IOPS, 512 burst.
+
+estimate_iops
+readpercentage: 0
+writesize: 65536
+----
+Write-only workload (64 KiB writes): 8.0 sustained IOPS, 128 burst.
+
+estimate_iops
+readpercentage: 0
+writesize: 1048576
+----
+Write-only workload (1.0 MiB writes): 0.5 sustained IOPS, 8.0 burst.
+
+estimate_iops
+readpercentage: 50
+readsize: 4096
+writesize: 4096
+----
+Mixed workload (50% reads; 4.0 KiB reads; 4.0 KiB writes): 256 sustained IOPS, 1024 burst.
+
+estimate_iops
+readpercentage: 90
+readsize: 4096
+writesize: 4096
+----
+Mixed workload (90% reads; 4.0 KiB reads; 4.0 KiB writes): 142 sustained IOPS, 569 burst.