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
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
|
package stmtcache
import (
"container/list"
"context"
"fmt"
"sync/atomic"
"github.com/jackc/pgconn"
)
var lruCount uint64
// LRU implements Cache with a Least Recently Used (LRU) cache.
type LRU struct {
conn *pgconn.PgConn
mode int
cap int
prepareCount int
m map[string]*list.Element
l *list.List
psNamePrefix string
stmtsToClear []string
}
// NewLRU creates a new LRU. mode is either ModePrepare or ModeDescribe. cap is the maximum size of the cache.
func NewLRU(conn *pgconn.PgConn, mode int, cap int) *LRU {
mustBeValidMode(mode)
mustBeValidCap(cap)
n := atomic.AddUint64(&lruCount, 1)
return &LRU{
conn: conn,
mode: mode,
cap: cap,
m: make(map[string]*list.Element),
l: list.New(),
psNamePrefix: fmt.Sprintf("lrupsc_%d", n),
}
}
// Get returns the prepared statement description for sql preparing or describing the sql on the server as needed.
func (c *LRU) Get(ctx context.Context, sql string) (*pgconn.StatementDescription, error) {
if ctx != context.Background() {
select {
case <-ctx.Done():
return nil, ctx.Err()
default:
}
}
// flush an outstanding bad statements
txStatus := c.conn.TxStatus()
if (txStatus == 'I' || txStatus == 'T') && len(c.stmtsToClear) > 0 {
for _, stmt := range c.stmtsToClear {
err := c.clearStmt(ctx, stmt)
if err != nil {
return nil, err
}
}
}
if el, ok := c.m[sql]; ok {
c.l.MoveToFront(el)
return el.Value.(*pgconn.StatementDescription), nil
}
if c.l.Len() == c.cap {
err := c.removeOldest(ctx)
if err != nil {
return nil, err
}
}
psd, err := c.prepare(ctx, sql)
if err != nil {
return nil, err
}
el := c.l.PushFront(psd)
c.m[sql] = el
return psd, nil
}
// Clear removes all entries in the cache. Any prepared statements will be deallocated from the PostgreSQL session.
func (c *LRU) Clear(ctx context.Context) error {
for c.l.Len() > 0 {
err := c.removeOldest(ctx)
if err != nil {
return err
}
}
return nil
}
func (c *LRU) StatementErrored(sql string, err error) {
pgErr, ok := err.(*pgconn.PgError)
if !ok {
return
}
// https://github.com/jackc/pgx/issues/1162
//
// We used to look for the message "cached plan must not change result type". However, that message can be localized.
// Unfortunately, error code "0A000" - "FEATURE NOT SUPPORTED" is used for many different errors and the only way to
// tell the difference is by the message. But all that happens is we clear a statement that we otherwise wouldn't
// have so it should be safe.
possibleInvalidCachedPlanError := pgErr.Code == "0A000"
if possibleInvalidCachedPlanError {
c.stmtsToClear = append(c.stmtsToClear, sql)
}
}
func (c *LRU) clearStmt(ctx context.Context, sql string) error {
elem, inMap := c.m[sql]
if !inMap {
// The statement probably fell off the back of the list. In that case, we've
// ensured that it isn't in the cache, so we can declare victory.
return nil
}
c.l.Remove(elem)
psd := elem.Value.(*pgconn.StatementDescription)
delete(c.m, psd.SQL)
if c.mode == ModePrepare {
return c.conn.Exec(ctx, fmt.Sprintf("deallocate %s", psd.Name)).Close()
}
return nil
}
// Len returns the number of cached prepared statement descriptions.
func (c *LRU) Len() int {
return c.l.Len()
}
// Cap returns the maximum number of cached prepared statement descriptions.
func (c *LRU) Cap() int {
return c.cap
}
// Mode returns the mode of the cache (ModePrepare or ModeDescribe)
func (c *LRU) Mode() int {
return c.mode
}
func (c *LRU) prepare(ctx context.Context, sql string) (*pgconn.StatementDescription, error) {
var name string
if c.mode == ModePrepare {
name = fmt.Sprintf("%s_%d", c.psNamePrefix, c.prepareCount)
c.prepareCount += 1
}
return c.conn.Prepare(ctx, name, sql, nil)
}
func (c *LRU) removeOldest(ctx context.Context) error {
oldest := c.l.Back()
c.l.Remove(oldest)
psd := oldest.Value.(*pgconn.StatementDescription)
delete(c.m, psd.SQL)
if c.mode == ModePrepare {
return c.conn.Exec(ctx, fmt.Sprintf("deallocate %s", psd.Name)).Close()
}
return nil
}
|
