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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
}
isInvalidCachedPlanError := pgErr.Severity == "ERROR" &&
pgErr.Code == "0A000" &&
pgErr.Message == "cached plan must not change result type"
if isInvalidCachedPlanError {
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
}
|
