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database_storage.go
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database_storage.go
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package remotecache
import (
"context"
"time"
"github.com/grafana/grafana/pkg/infra/log"
"github.com/grafana/grafana/pkg/services/sqlstore"
)
var getTime = time.Now
const databaseCacheType = "database"
type databaseCache struct {
SQLStore *sqlstore.SQLStore
log log.Logger
}
func newDatabaseCache(sqlstore *sqlstore.SQLStore) *databaseCache {
dc := &databaseCache{
SQLStore: sqlstore,
log: log.New("remotecache.database"),
}
return dc
}
func (dc *databaseCache) Run(ctx context.Context) error {
ticker := time.NewTicker(time.Minute * 10)
for {
select {
case <-ctx.Done():
return ctx.Err()
case <-ticker.C:
dc.internalRunGC()
}
}
}
func (dc *databaseCache) internalRunGC() {
err := dc.SQLStore.WithDbSession(context.Background(), func(session *sqlstore.DBSession) error {
now := getTime().Unix()
sql := `DELETE FROM cache_data WHERE (? - created_at) >= expires AND expires <> 0`
_, err := session.Exec(sql, now)
return err
})
if err != nil {
dc.log.Error("failed to run garbage collect", "error", err)
}
}
func (dc *databaseCache) Get(ctx context.Context, key string) (interface{}, error) {
cacheHit := CacheData{}
session := dc.SQLStore.NewSession(ctx)
defer session.Close()
exist, err := session.Where("cache_key= ?", key).Get(&cacheHit)
if err != nil {
return nil, err
}
if !exist {
return nil, ErrCacheItemNotFound
}
if cacheHit.Expires > 0 {
existedButExpired := getTime().Unix()-cacheHit.CreatedAt >= cacheHit.Expires
if existedButExpired {
err = dc.Delete(ctx, key) // ignore this error since we will return `ErrCacheItemNotFound` anyway
if err != nil {
dc.log.Debug("Deletion of expired key failed: %v", err)
}
return nil, ErrCacheItemNotFound
}
}
item := &cachedItem{}
if err = decodeGob(cacheHit.Data, item); err != nil {
return nil, err
}
return item.Val, nil
}
func (dc *databaseCache) Set(ctx context.Context, key string, value interface{}, expire time.Duration) error {
item := &cachedItem{Val: value}
data, err := encodeGob(item)
if err != nil {
return err
}
session := dc.SQLStore.NewSession(context.Background())
defer session.Close()
var expiresInSeconds int64
if expire != 0 {
expiresInSeconds = int64(expire) / int64(time.Second)
}
// attempt to insert the key
sql := `INSERT INTO cache_data (cache_key,data,created_at,expires) VALUES(?,?,?,?)`
_, err = session.Exec(sql, key, data, getTime().Unix(), expiresInSeconds)
if err != nil {
// attempt to update if a unique constrain violation or a deadlock (for MySQL) occurs
// if the update fails propagate the error
// which eventually will result in a key that is not finally set
// but since it's a cache does not harm a lot
if dc.SQLStore.Dialect.IsUniqueConstraintViolation(err) || dc.SQLStore.Dialect.IsDeadlock(err) {
sql := `UPDATE cache_data SET data=?, created_at=?, expires=? WHERE cache_key=?`
_, err = session.Exec(sql, data, getTime().Unix(), expiresInSeconds, key)
if err != nil && dc.SQLStore.Dialect.IsDeadlock(err) {
// most probably somebody else is upserting the key
// so it is safe enough not to propagate this error
return nil
}
}
}
return err
}
func (dc *databaseCache) Delete(ctx context.Context, key string) error {
return dc.SQLStore.WithDbSession(ctx, func(session *sqlstore.DBSession) error {
sql := "DELETE FROM cache_data WHERE cache_key=?"
_, err := session.Exec(sql, key)
return err
})
}
// CacheData is the struct representing the table in the database
type CacheData struct {
CacheKey string
Data []byte
Expires int64
CreatedAt int64
}