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balancer.go
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balancer.go
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// Copyright 2012, Google Inc. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
package vtgate
import (
"flag"
"fmt"
"math/rand"
"sort"
"sync"
"time"
log "github.com/golang/glog"
pb "github.com/youtube/vitess/go/vt/proto/topodata"
)
var resetDownConnDelay = flag.Duration("reset-down-conn-delay", 10*time.Minute, "delay to reset a marked down tabletconn")
// GetEndPointsFunc defines the callback to topo server.
type GetEndPointsFunc func() (*pb.EndPoints, error)
// Balancer is a simple round-robin load balancer.
// It allows you to temporarily mark down nodes that
// are non-functional.
type Balancer struct {
mu sync.Mutex
addressNodes []*addressStatus
index int
getEndPoints GetEndPointsFunc
retryDelay time.Duration
resetDownConnDelay time.Duration
}
type addressStatus struct {
endPoint *pb.EndPoint
timeRetry time.Time
balancer *Balancer
}
// NewBalancer creates a Balancer. getAddresses is the function
// it will use to refresh the list of addresses if one of the
// nodes has been marked down. The list of addresses is shuffled.
// retryDelay specifies the minimum time a node will be marked down
// before it will be cleared for a retry.
func NewBalancer(getEndPoints GetEndPointsFunc, retryDelay time.Duration) *Balancer {
blc := new(Balancer)
blc.getEndPoints = getEndPoints
blc.retryDelay = retryDelay
blc.resetDownConnDelay = *resetDownConnDelay
return blc
}
// Get returns a single endpoint that was not recently marked down.
// If it finds an address that was down for longer than retryDelay,
// it refreshes the list of addresses and returns the next available
// node. If all addresses are marked down, it waits and retries.
// If a refresh fails, it returns an error.
func (blc *Balancer) Get() (endPoints []*pb.EndPoint, err error) {
blc.mu.Lock()
defer blc.mu.Unlock()
// Clear timeRetry if it has been a long time
for _, addrNode := range blc.addressNodes {
if time.Now().Sub(addrNode.timeRetry) > blc.resetDownConnDelay {
addrNode.timeRetry = time.Time{}
}
}
// Get the latest endpoints
err = blc.refresh()
if err != nil {
return []*pb.EndPoint{}, err
}
// Return all endpoints without markdown and timeRetry < now(),
// so endpoints just marked down (within retryDelay) are ignored.
validEndPoints := make([]*pb.EndPoint, 0, 1)
for _, addrNode := range blc.addressNodes {
if addrNode.timeRetry.IsZero() || addrNode.timeRetry.Before(time.Now()) {
validEndPoints = append(validEndPoints, addrNode.endPoint)
continue
}
break
}
return validEndPoints, nil
}
// MarkDown marks the specified address down. Such addresses
// will not be used by Balancer for the duration of retryDelay.
func (blc *Balancer) MarkDown(uid uint32, reason string) {
blc.mu.Lock()
defer blc.mu.Unlock()
if index := findAddrNode(blc.addressNodes, uid); index != -1 {
log.Infof("Marking down %v at %+v (%v)", uid, blc.addressNodes[index].endPoint, reason)
blc.addressNodes[index].timeRetry = time.Now().Add(blc.retryDelay)
}
}
func (blc *Balancer) refresh() error {
endPoints, err := blc.getEndPoints()
if err != nil {
return err
}
// Add new addressNodes
if endPoints != nil {
for _, endPoint := range endPoints.Entries {
if index := findAddrNode(blc.addressNodes, endPoint.Uid); index == -1 {
addrNode := &addressStatus{
endPoint: endPoint,
balancer: blc,
}
blc.addressNodes = append(blc.addressNodes, addrNode)
} else {
blc.addressNodes[index].endPoint = endPoint
}
}
}
// Remove those that went away
i := 0
for i < len(blc.addressNodes) {
if index := findAddress(endPoints, blc.addressNodes[i].endPoint.Uid); index == -1 {
blc.addressNodes = delAddrNode(blc.addressNodes, i)
continue
}
i++
}
if len(blc.addressNodes) == 0 {
return fmt.Errorf("no available addresses")
}
// Sort endpoints by timeRetry (from ZERO to largest)
sort.Sort(AddressList(blc.addressNodes))
// Randomize endpoints with ZERO timeRetry
shuffle(blc.addressNodes, findFirstAddrNodeNonZeroTimeRetry(blc.addressNodes))
return nil
}
// AddressList is the slice of addressStatus.
type AddressList []*addressStatus
func (al AddressList) Len() int {
return len(al)
}
func (al AddressList) Swap(i, j int) {
al[i], al[j] = al[j], al[i]
}
func (al AddressList) Less(i, j int) bool {
return al[i].timeRetry.Before(al[j].timeRetry)
}
func findFirstAddrNodeNonZeroTimeRetry(addressNodes []*addressStatus) (index int) {
for i, addrNode := range addressNodes {
if !addrNode.timeRetry.IsZero() {
return i
}
}
return len(addressNodes)
}
func findAddrNode(addressNodes []*addressStatus, uid uint32) (index int) {
for i, addrNode := range addressNodes {
if uid == addrNode.endPoint.Uid {
return i
}
}
return -1
}
func findAddress(endPoints *pb.EndPoints, uid uint32) (index int) {
if endPoints == nil {
return -1
}
for i, endPoint := range endPoints.Entries {
if uid == endPoint.Uid {
return i
}
}
return -1
}
func delAddrNode(addressNodes []*addressStatus, index int) []*addressStatus {
copy(addressNodes[index:len(addressNodes)-1], addressNodes[index+1:])
return addressNodes[:len(addressNodes)-1]
}
// shuffle uses the Fisher-Yates algorithm.
func shuffle(addressNodes []*addressStatus, length int) {
index := 0
for i := length - 1; i > 0; i-- {
index = rand.Intn(i + 1)
addressNodes[i], addressNodes[index] = addressNodes[index], addressNodes[i]
}
}
func init() {
rand.Seed(time.Now().UnixNano())
idGen.Set(rand.Int63())
}