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net: implement query-response fast failover in builtin dns stub resolver

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Speed improvements via code cleanup, and changes to make go dns behave more like glibc resolver.  See https://groups.google.com/forum/#!topic/golang-dev/lV-0aHqxVeo

Fixes #6579.

Benchmark results on linux/amd64

benchmark                                  old ns/op    new ns/op    delta
BenchmarkGoLookupIP                          4831903      2572937  -46.75%
BenchmarkGoLookupIPNoSuchHost               10114105      2419641  -76.08%
BenchmarkGoLookupIPWithBrokenNameServer  20007735624   5004490730  -74.99%

benchmark                                 old allocs   new allocs    delta
BenchmarkGoLookupIP                              287          288    0.35%
BenchmarkGoLookupIPNoSuchHost                    204          102  -50.00%
BenchmarkGoLookupIPWithBrokenNameServer          410          358  -12.68%

benchmark                                  old bytes    new bytes    delta
BenchmarkGoLookupIP                            13181        13271    0.68%
BenchmarkGoLookupIPNoSuchHost                  17260         8714  -49.51%
BenchmarkGoLookupIPWithBrokenNameServer        28160        22432  -20.34%

LGTM=mikioh.mikioh
R=golang-codereviews, mikioh.mikioh, bradfitz, josharian, abursavich
CC=golang-codereviews
https://golang.org/cl/128820043
This commit is contained in:
Alex A Skinner 2014-08-30 13:12:28 +09:00 committed by Mikio Hara
parent 2758cb75f0
commit 39a021bc0e
2 changed files with 54 additions and 41 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

70
src/pkg/net/dnsclient_unix.go
View File

@ -169,33 +169,20 @@ func tryOneName(cfg *dnsConfig, name string, qtype uint16) (string, []dnsRR, err
}
timeout := time.Duration(cfg.timeout) * time.Second
var lastErr error
for _, server := range cfg.servers {
server += ":53"
lastErr = &DNSError{
Err: "no answer from DNS server",
Name: name,
Server: server,
IsTimeout: true,
}
for i := 0; i < cfg.attempts; i++ {
for _, server := range cfg.servers {
server = JoinHostPort(server, "53")
msg, err := exchange(server, name, qtype, timeout)
if err != nil {
if nerr, ok := err.(Error); ok && nerr.Timeout() {
lastErr = &DNSError{
Err: nerr.Error(),
Name: name,
Server: server,
IsTimeout: true,
}
continue
}
lastErr = &DNSError{
Err: err.Error(),
Name: name,
Server: server,
}
break
if nerr, ok := err.(Error); ok && nerr.Timeout() {
lastErr.(*DNSError).IsTimeout = true
}
continue
}
cname, addrs, err := answer(name, server, msg, qtype)
if err == nil || err.(*DNSError).Err == noSuchHost {
@ -387,31 +374,36 @@ func goLookupIP(name string) (addrs []IP, err error) {
return
}
}
var records []dnsRR
var cname string
var err4, err6 error
cname, records, err4 = lookup(name, dnsTypeA)
addrs = convertRR_A(records)
if cname != "" {
name = cname
type racer struct {
qtype uint16
rrs []dnsRR
error
}
_, records, err6 = lookup(name, dnsTypeAAAA)
if err4 != nil && err6 == nil {
// Ignore A error because AAAA lookup succeeded.
err4 = nil
lane := make(chan racer, 1)
qtypes := [...]uint16{dnsTypeA, dnsTypeAAAA}
for _, qtype := range qtypes {
go func(qtype uint16) {
_, rrs, err := lookup(name, qtype)
lane <- racer{qtype, rrs, err}
}(qtype)
}
if err6 != nil && len(addrs) > 0 {
// Ignore AAAA error because A lookup succeeded.
err6 = nil
var lastErr error
for range qtypes {
racer := <-lane
if racer.error != nil {
lastErr = racer.error
continue
}
if err4 != nil {
return nil, err4
switch racer.qtype {
case dnsTypeA:
addrs = append(addrs, convertRR_A(racer.rrs)...)
case dnsTypeAAAA:
addrs = append(addrs, convertRR_AAAA(racer.rrs)...)
}
if err6 != nil {
return nil, err6
}
addrs = append(addrs, convertRR_AAAA(records)...)
if len(addrs) == 0 && lastErr != nil {
return nil, lastErr
}
return addrs, nil
}

21
src/pkg/net/dnsclient_unix_test.go
View File

@ -218,8 +218,29 @@ func TestReloadResolvConfChange(t *testing.T) {
r.WantServers([]string{"[8.8.4.4]"})
}
func BenchmarkGoLookupIP(b *testing.B) {
for i := 0; i < b.N; i++ {
goLookupIP("www.example.com")
}
}
func BenchmarkGoLookupIPNoSuchHost(b *testing.B) {
for i := 0; i < b.N; i++ {
goLookupIP("some.nonexistent")
}
}
func BenchmarkGoLookupIPWithBrokenNameServer(b *testing.B) {
onceLoadConfig.Do(loadDefaultConfig)
if cfg.dnserr != nil || cfg.dnsConfig == nil {
b.Fatalf("loadConfig failed: %v", cfg.dnserr)
}
// This looks ugly but it's safe as long as benchmarks are run
// sequentially in package testing.
orig := cfg.dnsConfig
cfg.dnsConfig.servers = append([]string{"203.0.113.254"}, cfg.dnsConfig.servers...) // use TEST-NET-3 block, see RFC 5737
for i := 0; i < b.N; i++ {
goLookupIP("www.example.com")
}
cfg.dnsConfig = orig
}