/
backoff.go
259 lines (232 loc) · 6.8 KB
/
backoff.go
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// Copyright 2018 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 retry
import (
"context"
"fmt"
"math"
"math/rand"
"time"
"github.com/pkg/errors"
log "github.com/sirupsen/logrus"
"github.com/tikv/client-go/metrics"
)
const (
// NoJitter makes the backoff sequence strict exponential.
NoJitter = 1 + iota
// FullJitter applies random factors to strict exponential.
FullJitter
// EqualJitter is also randomized, but prevents very short sleeps.
EqualJitter
// DecorrJitter increases the maximum jitter based on the last random value.
DecorrJitter
)
// NewBackoffFn creates a backoff func which implements exponential backoff with
// optional jitters.
// See http://www.awsarchitectureblog.com/2015/03/backoff.html
func NewBackoffFn(base, cap, jitter int) func(ctx context.Context) int {
if base < 2 {
// Top prevent panic in 'rand.Intn'.
base = 2
}
attempts := 0
lastSleep := base
return func(ctx context.Context) int {
var sleep int
switch jitter {
case NoJitter:
sleep = expo(base, cap, attempts)
case FullJitter:
v := expo(base, cap, attempts)
sleep = rand.Intn(v)
case EqualJitter:
v := expo(base, cap, attempts)
sleep = v/2 + rand.Intn(v/2)
case DecorrJitter:
sleep = int(math.Min(float64(cap), float64(base+rand.Intn(lastSleep*3-base))))
}
log.Debugf("backoff base %d, sleep %d", base, sleep)
select {
case <-time.After(time.Duration(sleep) * time.Millisecond):
case <-ctx.Done():
}
attempts++
lastSleep = sleep
return lastSleep
}
}
func expo(base, cap, n int) int {
return int(math.Min(float64(cap), float64(base)*math.Pow(2.0, float64(n))))
}
// BackoffType is the retryable error type.
type BackoffType int
// Back off types.
const (
BoTiKVRPC BackoffType = iota
BoTxnLock
BoTxnLockFast
BoPDRPC
BoRegionMiss
BoUpdateLeader
BoServerBusy
)
func (t BackoffType) createFn() func(context.Context) int {
switch t {
case BoTiKVRPC:
return NewBackoffFn(100, 2000, EqualJitter)
case BoTxnLock:
return NewBackoffFn(200, 3000, EqualJitter)
case BoTxnLockFast:
return NewBackoffFn(50, 3000, EqualJitter)
case BoPDRPC:
return NewBackoffFn(500, 3000, EqualJitter)
case BoRegionMiss:
// change base time to 2ms, because it may recover soon.
return NewBackoffFn(2, 500, NoJitter)
case BoUpdateLeader:
return NewBackoffFn(1, 10, NoJitter)
case BoServerBusy:
return NewBackoffFn(2000, 10000, EqualJitter)
}
return nil
}
func (t BackoffType) String() string {
switch t {
case BoTiKVRPC:
return "tikvRPC"
case BoTxnLock:
return "txnLock"
case BoTxnLockFast:
return "txnLockFast"
case BoPDRPC:
return "pdRPC"
case BoRegionMiss:
return "regionMiss"
case BoUpdateLeader:
return "updateLeader"
case BoServerBusy:
return "serverBusy"
}
return ""
}
// Maximum total sleep time(in ms) for kv/cop commands.
const (
CopBuildTaskMaxBackoff = 5000
TsoMaxBackoff = 15000
ScannerNextMaxBackoff = 20000
BatchGetMaxBackoff = 20000
CopNextMaxBackoff = 20000
GetMaxBackoff = 20000
PrewriteMaxBackoff = 20000
CleanupMaxBackoff = 20000
GcOneRegionMaxBackoff = 20000
GcResolveLockMaxBackoff = 100000
DeleteRangeOneRegionMaxBackoff = 100000
RawkvMaxBackoff = 20000
SplitRegionBackoff = 20000
)
// CommitMaxBackoff is max sleep time of the 'commit' command
var CommitMaxBackoff = 41000
// Backoffer is a utility for retrying queries.
type Backoffer struct {
ctx context.Context
fn map[BackoffType]func(context.Context) int
maxSleep int
totalSleep int
errors []error
types []BackoffType
}
// txnStartKey is a key for transaction start_ts info in context.Context.
const txnStartKey = "_txn_start_key"
// NewBackoffer creates a Backoffer with maximum sleep time(in ms).
func NewBackoffer(ctx context.Context, maxSleep int) *Backoffer {
return &Backoffer{
ctx: ctx,
maxSleep: maxSleep,
}
}
// Backoff sleeps a while base on the BackoffType and records the error message.
// It returns a retryable error if total sleep time exceeds maxSleep.
func (b *Backoffer) Backoff(typ BackoffType, err error) error {
select {
case <-b.ctx.Done():
return err
default:
}
metrics.BackoffCounter.WithLabelValues(typ.String()).Inc()
// Lazy initialize.
if b.fn == nil {
b.fn = make(map[BackoffType]func(context.Context) int)
}
f, ok := b.fn[typ]
if !ok {
f = typ.createFn()
b.fn[typ] = f
}
b.totalSleep += f(b.ctx)
b.types = append(b.types, typ)
var startTs interface{}
if ts := b.ctx.Value(txnStartKey); ts != nil {
startTs = ts
}
log.Debugf("%v, retry later(totalsleep %dms, maxsleep %dms), type: %s, txn_start_ts: %v", err, b.totalSleep, b.maxSleep, typ.String(), startTs)
b.errors = append(b.errors, errors.Errorf("%s at %s", err.Error(), time.Now().Format(time.RFC3339Nano)))
if b.maxSleep > 0 && b.totalSleep >= b.maxSleep {
errMsg := fmt.Sprintf("backoffer.maxSleep %dms is exceeded, errors:", b.maxSleep)
for i, err := range b.errors {
// Print only last 3 errors for non-DEBUG log levels.
if log.GetLevel() == log.DebugLevel || i >= len(b.errors)-3 {
errMsg += "\n" + err.Error()
}
}
log.Warn(errMsg)
// Use the first backoff type to generate a MySQL error.
return errors.New(b.types[0].String())
}
return nil
}
func (b *Backoffer) String() string {
if b.totalSleep == 0 {
return ""
}
return fmt.Sprintf(" backoff(%dms %v)", b.totalSleep, b.types)
}
// Clone creates a new Backoffer which keeps current Backoffer's sleep time and errors, and shares
// current Backoffer's context.
func (b *Backoffer) Clone() *Backoffer {
return &Backoffer{
ctx: b.ctx,
maxSleep: b.maxSleep,
totalSleep: b.totalSleep,
errors: b.errors,
}
}
// Fork creates a new Backoffer which keeps current Backoffer's sleep time and errors, and holds
// a child context of current Backoffer's context.
func (b *Backoffer) Fork() (*Backoffer, context.CancelFunc) {
ctx, cancel := context.WithCancel(b.ctx)
return &Backoffer{
ctx: ctx,
maxSleep: b.maxSleep,
totalSleep: b.totalSleep,
errors: b.errors[:len(b.errors):len(b.errors)],
}, cancel
}
// GetContext returns the associated context.
func (b *Backoffer) GetContext() context.Context {
return b.ctx
}
// TotalSleep returns the total sleep time of the backoffer.
func (b *Backoffer) TotalSleep() time.Duration {
return time.Duration(b.totalSleep) * time.Millisecond
}