-
Notifications
You must be signed in to change notification settings - Fork 82
/
taf.go
140 lines (127 loc) · 4.39 KB
/
taf.go
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
// Copyright 2019 PayPal Inc.
//
// Licensed to the Apache Software Foundation (ASF) under one or more
// contributor license agreements. See the NOTICE file distributed with
// this work for additional information regarding copyright ownership.
// The ASF licenses this file to You 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,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
package lib
import (
"fmt"
"github.com/paypal/hera/utility/logger"
"math/rand"
"sync/atomic"
)
// TAF keeps a statistic of errors and successes and tells which database whould be used for the next request
type TAF interface {
// return true if the request should use the primary db, false to use the fallback
UsePrimary() bool
// For logging, gets the internal PCT field, which is a measure of the health of the primary database
GetPct() int
// To be called by coordinator if the request was ok
NotifyOK()
// To be called by coordinator if the request timed out failed with an ORA error
NotifyError()
}
var giTAF []*taf
// GetTAF returns the TAF entry for the shard
func GetTAF(shard int) TAF {
return giTAF[shard]
}
const (
tafMaxPct = uint32(110)
tafMinPct = uint32(1)
// pct change for recovery as well as max pct change for failure
tafPctChange = uint32(10)
tafDeltaPctMin = uint32(1)
tafDeltaPctMax = uint32(64)
)
/**
* taf implements TAF interface
*/
type taf struct {
// pct is the probability of going to the primary database on the next request. It is in [1..110] range,
// it decreases when we see falures in the primary and it increases when we see successes in the primary.
// 1 is the lower bound because even if the primary is down completely we still send 1% of requests to the primary,
// as a way of doing health check. 110 is the upper bound because a spurrious error should not cause moving away
// from the primary, we still send 100% of requests to the primary
pct uint32
// deltaPct is by how much we change pct
deltaPct uint32
shard int
}
// InitTAF initializes the TAF structure
func InitTAF(shards int) {
giTAF = make([]*taf, shards, shards)
for tf := range giTAF {
giTAF[tf] = &taf{pct: tafMaxPct, deltaPct: 1, shard: tf}
}
}
// UsePrimary tells if it should use the primary
func (tf *taf) UsePrimary() bool {
return uint32(rand.Intn(100)) < atomic.LoadUint32(&(tf.pct))
}
// GetPct returns the current value of PCT
func (tf *taf) GetPct() int {
return int(tf.pct)
}
// NotifyOK increases pct by 10 and halves deltaPct
func (tf *taf) NotifyOK() {
// we ignore race condition because we don't have to be precise. so no need for CAS
pct := atomic.LoadUint32(&(tf.pct))
deltaPct := atomic.LoadUint32(&(tf.deltaPct))
if pct < tafMaxPct {
if pct < tafMaxPct-tafPctChange {
pct += tafPctChange
} else {
pct = tafMaxPct
}
atomic.StoreUint32(&(tf.pct), pct)
}
if deltaPct > tafDeltaPctMin {
deltaPct /= 2
atomic.StoreUint32(&(tf.deltaPct), deltaPct)
}
if logger.GetLogger().V(logger.Verbose) {
logger.GetLogger().Log(logger.Verbose, "TAF NotifyOK: pct =", pct, ", deltaPct:", deltaPct, ", shard:", tf.shard)
}
}
// NotifyError decreases pct by max(10, deltaPct) and doubles deltaPct
func (tf *taf) NotifyError() {
// we ignore race condition because we don't have to be precise. so no need for CAS
pct := atomic.LoadUint32(&(tf.pct))
oldDeltaPct := atomic.LoadUint32(&(tf.deltaPct))
if pct > tafMinPct {
var deltaPct uint32
if oldDeltaPct > tafPctChange {
deltaPct = tafPctChange
} else {
deltaPct = oldDeltaPct
}
if pct > tafMinPct+deltaPct {
pct -= deltaPct
} else {
pct = tafMinPct
}
atomic.StoreUint32(&(tf.pct), pct)
}
if oldDeltaPct < tafDeltaPctMax {
oldDeltaPct *= 2
atomic.StoreUint32(&(tf.deltaPct), oldDeltaPct)
}
if logger.GetLogger().V(logger.Verbose) {
logger.GetLogger().Log(logger.Verbose, "TAF NotifyError: pct =", pct, ", deltaPct:", oldDeltaPct, ", shard:", tf.shard)
}
}
func (tf *taf) dump() string {
return fmt.Sprintf("TAFLB pct=%d%%, deltaPct=%d%%, shard=%d\n", tf.pct, tf.deltaPct, tf.shard)
}