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pkg/log(dm):support reading fields from Ctx #5518

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May 24, 2022
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47 changes: 47 additions & 0 deletions dm/pkg/log/ctx.go
Original file line number Diff line number Diff line change
@@ -0,0 +1,47 @@
// Copyright 2022 PingCAP, Inc.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// See the License for the specific language governing permissions and
// limitations under the License.

package log

import (
"context"

"go.uber.org/zap"
)

type logCtxKeyType string

var logCtxKey = logCtxKeyType("zap-fields")

func getZapFieldsFromCtx(ctx context.Context) []zap.Field {
// Use a pointer to key to save one allocation.
fields := ctx.Value(&logCtxKey)
if fields == nil {
return nil
}
// Note that the value is a pointer to slice, to save allocation.
return *fields.(*[]zap.Field)
}

// AppendZapFieldToCtx attaches new fields to the context, which can be then
// used with log.WithCtx().
func AppendZapFieldToCtx(ctx context.Context, newFields ...zap.Field) context.Context {
fields := getZapFieldsFromCtx(ctx)
if fields == nil {
// 8 fields should be enough for most situations.
fields = make([]zap.Field, 0, 8)
}
fields = append(fields, newFields...)

return context.WithValue(ctx, &logCtxKey, &fields)
}
57 changes: 57 additions & 0 deletions dm/pkg/log/ctx_test.go
Original file line number Diff line number Diff line change
@@ -0,0 +1,57 @@
// Copyright 2022 PingCAP, Inc.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// See the License for the specific language governing permissions and
// limitations under the License.

package log

import (
"context"
"fmt"
"testing"

"github.com/stretchr/testify/require"
"go.uber.org/zap"
)

func TestLogCtxBasics(t *testing.T) {
ctx := context.Background()
ctx1 := AppendZapFieldToCtx(ctx, zap.String("key1", "value1"))
ctx2 := AppendZapFieldToCtx(ctx1, zap.String("key2", "value2"))

require.Nil(t, getZapFieldsFromCtx(ctx))
require.Equal(t, []zap.Field{zap.String("key1", "value1")}, getZapFieldsFromCtx(ctx1))
require.Equal(t, []zap.Field{
zap.String("key1", "value1"),
zap.String("key2", "value2"),
}, getZapFieldsFromCtx(ctx2))
}

func TestLogCtxTooManyFields(t *testing.T) {
ctx := context.Background()
var (
ctxs []context.Context
fields [][]zap.Field
)

ctxs = append(ctxs, ctx)
fields = append(fields, nil)
for i := 1; i < 100; i++ {
k := fmt.Sprintf("key%d", i)
v := fmt.Sprintf("value%d", i)
ctxs = append(ctxs, AppendZapFieldToCtx(ctxs[i-1], zap.String(k, v)))
fields = append(fields, append(fields[i-1], zap.String(k, v)))
}

for i := 0; i < 100; i++ {
require.Equal(t, fields[i], getZapFieldsFromCtx(ctxs[i]), "failed, index = %d", i)
}
}
5 changes: 5 additions & 0 deletions dm/pkg/log/log.go
Original file line number Diff line number Diff line change
Expand Up @@ -183,3 +183,8 @@ func WrapStringerField(message string, object fmt.Stringer) zap.Field {

return zap.Stringer(message, object)
}

// WithCtx adds fields from ctx to the logger.
func WithCtx(ctx context.Context) Logger {
return Logger{appLogger.With(getZapFieldsFromCtx(ctx)...)}
}
34 changes: 34 additions & 0 deletions dm/pkg/log/log_test.go
Original file line number Diff line number Diff line change
Expand Up @@ -150,3 +150,37 @@ func (s *testLogSuite) TestInitSlowQueryLoggerNotInDebugLevel(c *C) {
c.Assert(output[0], Matches, ".*this is from applogger.*")
c.Assert(output[1], Equals, "") // no output
}

func (s *testLogSuite) TestWithCtx(c *C) {
// test slow query logger can write debug log
logLevel := "debug"
cfg := &Config{Level: logLevel, Format: "json"}
cfg.Adjust()

ctx := context.Background()
ctx = AppendZapFieldToCtx(ctx, zap.String("key1", "value1"))
ctx = AppendZapFieldToCtx(ctx, zap.String("key2", "value2"))

output, err := captureStdout(func() {
c.Assert(InitLogger(cfg), IsNil)
WithCtx(ctx).Info("test1")
})
c.Assert(err, IsNil)
c.Assert(output[0], Matches, ".*test1.*key1.*value1.*key2.*value2.*")
}

func BenchmarkBaseline(b *testing.B) {
logger := L().With(zap.String("key1", "value1"))
for i := 0; i < b.N; i++ {
subLogger := logger.With(zap.String("key2", "value2"))
subLogger.Info("test-test-test")
}
}

func BenchmarkWithCtx(b *testing.B) {
ctx := AppendZapFieldToCtx(context.Background(), zap.String("key1", "value1"))
for i := 0; i < b.N; i++ {
subCtx := AppendZapFieldToCtx(ctx, zap.String("key2", "value2"))
WithCtx(subCtx).Info("test-test-test")
}
}