_clearExpiredHourAgo() {
    if (this._clearExpiredTimeoutId) {
      clearTimeout(this._clearExpiredTimeoutId);
    }
    this._clearExpiredTimeoutId = setTimeout(() => {
      this.clearExpired(Date.now() - 3600000) // Never rejected
        .then(() => {
          this._clearExpiredHourAgo();
        });
    }, 300000);
    this._clearExpiredTimeoutId.unref();
  }
Delete all rows expired 1 hour ago once per 5 minutes

@private