老师为什么我tc1()用了批处理的执行出来反而比不用批处理的tc2()慢了

package com.imooc.jdbc.sample;

import com.imooc.jdbc.common.DbUtils;

import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.SQLException;
import java.util.Date;

public class BatchSample {
    public static void tc1(){
        //批量添加1000名员工
        Connection conn = null;
        PreparedStatement pstmt = null;
        try {
            long startTime = new Date().getTime();
            conn = DbUtils.getConnection();
            String sql = "insert into employee(eno,ename,salary,dname) values(?,?,?,?)";
            pstmt = conn.prepareStatement(sql);
            for(int i=10000;i<20000;i++){
                conn.setAutoCommit(false);
                //若不使用手动提交事务模式，遇到事故时，会出现事情做一半的情况
//                if(i==1005){
//                    throw new RuntimeException("插入失败");
//                }
                pstmt.setInt(1,i);
                pstmt.setNString(2,"员工"+i);
                pstmt.setFloat(3,4000f);
                pstmt.setNString(4,"市场部");
                pstmt.addBatch();//将参数加入批处理
//                pstmt.executeUpdate();
            }
            pstmt.executeBatch();
            conn.commit();//提交数据
            long endTime = new Date().getTime();
            System.out.println("tc1执行时长为"+(endTime-startTime));
        } catch (Exception e) {
            e.printStackTrace();
            try {
                if(conn != null && !conn.isClosed()){
                    conn.rollback();//回滚数据
                }
            } catch (SQLException ex) {
                throw new RuntimeException(ex);
            }
        } finally{
            DbUtils.closeConnection(null,pstmt,conn);
        }
    }
    public static void tc2(){
        //批量添加1000名员工
        Connection conn = null;
        PreparedStatement pstmt = null;
        try {
            conn = DbUtils.getConnection();
            long startTime = new Date().getTime();
            String sql = "insert into employee(eno,ename,salary,dname) values(?,?,?,?)";
            for(int i=20000;i<30000;i++){
                conn.setAutoCommit(false);
                //若不使用手动提交事务模式，遇到事故时，会出现事情做一半的情况
//                if(i==1005){
//                    throw new RuntimeException("插入失败");
//                }
                pstmt = conn.prepareStatement(sql);
                pstmt.setInt(1,i);
                pstmt.setNString(2,"员工"+i);
                pstmt.setFloat(3,4000f);
                pstmt.setNString(4,"市场部");
                pstmt.executeUpdate();
            }
            conn.commit();//提交数据
            long endTime = new Date().getTime();
            System.out.println("tc2执行时长为"+(endTime-startTime));
        } catch (Exception e) {
            e.printStackTrace();
            try {
                if(conn != null && !conn.isClosed()){
                    conn.rollback();//回滚数据
                }
            } catch (SQLException ex) {
                throw new RuntimeException(ex);
            }
        } finally{
            DbUtils.closeConnection(null,pstmt,conn);
        }
    }

    public static void main(String[] args) {
        tc1();
        tc2();
    }
}

结果：
tc1执行时长为1893
tc2执行时长为1740