feat(benchmark): use gops to diagnose benchmark tool (#717)

### What this PR does

This pull request adds the gops agent into the benchmark tool, making it easier
to diagnose.

Refs:

- <https://github.com/google/gops>

cmd/benchmark/test_command.go

@@ -4,6 +4,7 @@ import (
 	"fmt"
 	"strings"
 
+	"github.com/google/gops/agent"
 	"github.com/urfave/cli/v2"
 
 	"github.com/kakao/varlog/internal/benchmark"
@@ -45,6 +46,12 @@ var (
 		Category: "Common: ",
 		Usage:    "Use single connection shared by appenders in a target. Each target uses different connection.",
 	}
+	flagGopsAddr = &cli.StringFlag{
+		Name:     "gops-addr",
+		Category: "Common: ",
+		Value:    ":0",
+		Usage:    "The address of gops agent",
+	}
 
 	flagAppenders = &cli.UintSliceFlag{
 		Name:     "appenders",
@@ -94,17 +101,21 @@ func newCommandTest() *cli.Command {
 		Usage: "run benchmark test",
 		Flags: []cli.Flag{
 			flagClusterID,
+
 			flagTarget,
 			flagMRAddrs,
-			flagMsgSize,
-			flagBatchSize,
-			flagAppenders,
-			flagSubscribers,
 			flagDuration,
 			flagReportInterval,
 			flagPrintJSON,
-			flagPipelineSize,
 			flagSingleConnPerTarget,
+			flagGopsAddr,
+
+			flagAppenders,
+			flagMsgSize,
+			flagBatchSize,
+			flagPipelineSize,
+
+			flagSubscribers,
 			flagSubscribeSize,
 		},
 		Action: runCommandTest,
@@ -116,6 +127,13 @@ func runCommandTest(c *cli.Context) error {
 		return fmt.Errorf("unexpected args: %v", c.Args().Slice())
 	}
 
+	if err := agent.Listen(agent.Options{
+		Addr: c.String(flagGopsAddr.Name),
+	}); err != nil {
+		return err
+	}
+	defer agent.Close()
+
 	clusterID, err := types.ParseClusterID(c.String(flagClusterID.Name))
 	if err != nil {
 		return err

go.mod

@@ -8,6 +8,7 @@ require (
 	github.com/gogo/protobuf v1.3.2
 	github.com/gogo/status v1.1.1
 	github.com/golang/protobuf v1.5.3
+	github.com/google/gops v0.3.28
 	github.com/lib/pq v1.10.9
 	github.com/pkg/errors v0.9.1
 	github.com/puzpuzpuz/xsync/v2 v2.5.1

go.sum

@@ -179,6 +179,8 @@ github.com/google/go-cmp v0.6.0/go.mod h1:17dUlkBOakJ0+DkrSSNjCkIjxS6bF9zb3elmeN
 github.com/google/gofuzz v1.0.0/go.mod h1:dBl0BpW6vV/+mYPU4Po3pmUjxk6FQPldtuIdl/M65Eg=
 github.com/google/gofuzz v1.2.0 h1:xRy4A+RhZaiKjJ1bPfwQ8sedCA+YS2YcCHW6ec7JMi0=
 github.com/google/gofuzz v1.2.0/go.mod h1:dBl0BpW6vV/+mYPU4Po3pmUjxk6FQPldtuIdl/M65Eg=
+github.com/google/gops v0.3.28 h1:2Xr57tqKAmQYRAfG12E+yLcoa2Y42UJo2lOrUFL9ark=
+github.com/google/gops v0.3.28/go.mod h1:6f6+Nl8LcHrzJwi8+p0ii+vmBFSlB4f8cOOkTJ7sk4c=
 github.com/google/martian v2.1.0+incompatible/go.mod h1:9I4somxYTbIHy5NJKHRl3wXiIaQGbYVAs8BPL6v8lEs=
 github.com/google/martian/v3 v3.0.0/go.mod h1:y5Zk1BBys9G+gd6Jrk0W3cC1+ELVxBWuIGO+w/tUAp0=
 github.com/google/pprof v0.0.0-20181206194817-3ea8567a2e57/go.mod h1:zfwlbNMJ+OItoe0UupaVj+oy1omPYYDuagoSzA8v9mc=

internal/benchmark/loader.go

@@ -248,11 +248,8 @@ func (loader *Loader) subscribeLoop(ctx context.Context, c varlog.Log) error {
 }
 
 func (loader *Loader) subscribeLoopInternal(ctx context.Context, c varlog.Log, first, last varlogpb.LogSequenceNumber) error {
-	subscribeSize := types.GLSN(loader.SubscribeSize)
-
-	loader.logger.Info("subscribe", slog.Any("first", first), slog.Any("last", last), slog.Int("subscribeSize", loader.SubscribeSize))
-
 	var sm SubscribeMetrics
+	subscribeSize := types.GLSN(loader.SubscribeSize)
 	begin := first.GLSN
 	end := min(begin+subscribeSize, last.GLSN+1)
 	for begin < end {