func (engine *Engine) BufferSize(size int) *Session {
	session := engine.NewSession()
	session.isAutoClose = true
	return session.BufferSize(size)
}
BufferSize sets buffer size for iterate
package xorm
import (
	"bufio"
	"bytes"
	"database/sql"
	"encoding/gob"
	"errors"
	"fmt"
	"io"
	"os"
	"reflect"
	"strconv"
	"strings"
	"sync"
	"time"
	"github.com/go-xorm/builder"
	"github.com/go-xorm/core"
)
type Engine struct {
	db      *core.DB
	dialect core.Dialect
	ColumnMapper  core.IMapper
	TableMapper   core.IMapper
	TagIdentifier string
	Tables        map[reflect.Type]*core.Table
	mutex  *sync.RWMutex
	Cacher core.Cacher
	showSQL      bool
	showExecTime bool
	logger     core.ILogger
	TZLocation *time.Location  
	DatabaseTZ *time.Location  
	disableGlobalCache bool
	tagHandlers map[string]tagHandler
	engineGroup *EngineGroup
}