func RemoveOlds() {
	if cfg.RecentRange <= 0 {
		return
	}
	t := time.Now().Unix() - cfg.RecentRange
	err := db.DB.Update(func(tx *bolt.Tx) error {
		ba := tx.Bucket([]byte("recent"))
		if ba == nil {
			return errors.New("bucket is not found")
		}
		c := ba.Cursor()
		for k, v := c.First(); k != nil; k, v = c.Next() {
			var m record.Head
			if err := json.Unmarshal(v, &m); err != nil {
				return err
			}
			if m.Stamp > t {
				continue
			}
			if err := c.Delete(); err != nil {
				log.Println(err)
			}
		}
		return nil
	})
	if err != nil {
		log.Println(err)
	}
}
RemoveOlds remove old records..
package recentlist
import (
	"errors"
	"log"
	"strconv"
	"strings"
	"sync"
	"time"
	"encoding/json"
	"github.com/boltdb/bolt"
	"github.com/shingetsu-gou/shingetsu-gou/cfg"
	"github.com/shingetsu-gou/shingetsu-gou/db"
	"github.com/shingetsu-gou/shingetsu-gou/node"
	"github.com/shingetsu-gou/shingetsu-gou/node/manager"
	"github.com/shingetsu-gou/shingetsu-gou/record"
	"github.com/shingetsu-gou/shingetsu-gou/tag/suggest"
)
const defaultUpdateRange = 24 * time.Hour  
func IsInUpdateRange(nstamp int64) bool {
	now := time.Now()
	if now.Add(-defaultUpdateRange).Unix() < nstamp && nstamp < now.Add(defaultUpdateRange).Unix() {
		return true
	}
	return false
}
func Datfiles() []string {
	var datfile []string
	err := db.DB.View(func(tx *bolt.Tx) error {
		var err error
		datfile, err = db.GetPrefixs(tx, "recent")
		return err
	})
	if err != nil {
		log.Print(err)
	}
	return datfile
}
func Newest(datfile string) (*record.Head, error) {
	var rows []string
	err := db.DB.View(func(tx *bolt.Tx) error {
		var err error
		rows, err = db.GetStrings(tx, "recent", []byte(datfile))
		return err
	})
	if err != nil {
		log.Print(err)
		return nil, err
	}
	if len(rows) == 0 {
		return nil, errors.New("not found")
	}
	newest := []byte(rows[len(rows)-1])
	r := record.Head{}
	err = json.Unmarshal(newest, &r)
	if err != nil {
		log.Println(err)
	}
	return &r, err
}
func appendHead(tx *bolt.Tx, rec *record.Head) {
	if find(rec) {
		return
	}
	k := rec.ToKey()
	err := db.Put(tx, "recent", k, rec)
	if err != nil {
		log.Print(err)
	}
}
func Append(rec *record.Head) {
	err := db.DB.Update(func(tx *bolt.Tx) error {
		appendHead(tx, rec)
		return nil
	})
	if err != nil {
		log.Println(err)
	}
}
func find(rec *record.Head) bool {
	k := rec.ToKey()
	var r int
	err := db.DB.View(func(tx *bolt.Tx) error {
		var err error
		r, err = db.Count(tx, "recent", k)
		return err
	})
	if err != nil {
		log.Print(err)
	}
	return r > 0
}