pkg: create package traceutil for tracing. mvcc: add tracing

steps:range from the in-memory index tree; range from boltdb.
etcdserver: add tracing steps: agreement among raft nodes before
linerized reading; authentication; filter and sort kv pairs; assemble
the response.

pkg/traceutil/trace.go

@@ -0,0 +1,60 @@
+package traceutil
+
+import (
+	"bytes"
+	"fmt"
+	"time"
+
+	"github.com/coreos/pkg/capnslog"
+	"go.uber.org/zap"
+)
+
+var (
+	plog = capnslog.NewPackageLogger("go.etcd.io/etcd", "trace")
+)
+
+type Trace struct {
+	operation string
+	startTime time.Time
+	steps     []step
+}
+
+type step struct {
+	time time.Time
+	msg  string
+}
+
+func New(op string) *Trace {
+	return &Trace{operation: op, startTime: time.Now()}
+}
+
+func (t *Trace) Step(msg string) {
+	t.steps = append(t.steps, step{time: time.Now(), msg: msg})
+}
+
+// Dump all steps in the Trace
+func (t *Trace) Log(lg *zap.Logger) {
+
+	var buf bytes.Buffer
+
+	buf.WriteString(fmt.Sprintf("The tracing of %v request:\n", t.operation))
+
+	buf.WriteString("Request started at:")
+	buf.WriteString(t.startTime.Format("2006-01-02 15:04:05"))
+	buf.WriteString(fmt.Sprintf(".%06d", t.startTime.Nanosecond()/1000))
+	buf.WriteString("\n")
+	lastStepTime := t.startTime
+	for i, step := range t.steps {
+		buf.WriteString(fmt.Sprintf("Step %d: %v Time cost: %v\n", i, step.msg, step.time.Sub(lastStepTime)))
+		//fmt.Println(step.msg, " costs: ", step.time.Sub(lastStepTime))
+		lastStepTime = step.time
+	}
+	buf.WriteString("Trace End\n")
+
+	s := buf.String()
+	if lg != nil {
+		lg.Info(s)
+	} else {
+		plog.Info(s)
+	}
+}

pkg/traceutil/trace_test.go

@@ -0,0 +1,28 @@
+package traceutil
+
+import (
+	"testing"
+)
+
+func TestTrace(t *testing.T) {
+	var (
+		op    = "Test"
+		steps = []string{"Step1, Step2"}
+	)
+
+	trace := New(op)
+	if trace.operation != op {
+		t.Errorf("Expected %v, got %v\n", op, trace.operation)
+	}
+
+	for _, v := range steps {
+		trace.Step(v)
+		trace.Step(v)
+	}
+
+	for i, v := range steps {
+		if v != trace.steps[i].msg {
+			t.Errorf("Expected %v, got %v\n.", v, trace.steps[i].msg)
+		}
+	}
+}