在Oracle中快速创建一张百万级别的表，一张十万级别的表 并修改两表中1%的数据 全部运行时间66秒

万以下小表做性能优化没有多大意义，因此我需要创建大表；

创建大表有三种方法，一种是insert into table selec..connect by.的方式，它最快但是数据要么是连续值，要么是随机值或是系统值，并不好用，而且总量上受到限制；另一种方法是用程序，借助Oracle的批量插值语法插入数据，它好在数据可以用程序掌控，总量也没有限制，缺点是速度慢；还有一种方法是有一张大表，把它的数据倒腾进来，语法是 insert into newtable select * from oldtable，这种方法暂时不在我的考虑之列。

为了节约时间，我采用了两种结合的办法，即用第一种方式先大量建立数据，再用程序修改其中一部分。

下面进入正题：

百万级别的表建表语句是这样的：

CREATE TABLE bigtable
(
    id NUMBER not null primary key,
    name NVARCHAR2(60) not null,
    score NUMBER(4,0) NOT NULL,
    createtime TIMESTAMP (6) not null
)

给它塞入百万数据可以这样做：

 Insert into bigtable
 select rownum,dbms_random.string('*',dbms_random.value(6,20)),dbms_random.value(0,20),sysdate from dual
 connect by level<=1000000
 order by dbms_random.random

使用上面这个方法，在我的T440p机器上实验，一次性创建的记录数大约在两百万到三百万之间，再多就会报“

第 1 行出现错误:
ORA-30009: CONNECT BY 操作内存不足

”看来机器性能在制约我的研究。

看看它的运行数据如何：

 已创建1000000行。

已用时间:  00: 00: 39.87

近四十秒创建百万数据，还不错。

十万级别的表结构如下：

create table smalltable
(
    id NUMBER not null primary key,
    name NVARCHAR2(60) not null,
    createtime TIMESTAMP (6) not null
)

同样的方式给它塞入数据：

 Insert into smalltable
 select rownum,dbms_random.string('*',dbms_random.value(6,20)),sysdate from dual
 connect by level<=100000
 order by dbms_random.random

发现4秒不到就搞定了：

 已创建100000行。

已用时间:  00: 00: 03.71

当然这样的数据还不够，于是下面的程序登场了，它的作用是将某表中百分之一记录的name字段改写成设定数组中的随机值：

package com.ufo;

public class DBParam {
    public final static String Driver = "oracle.jdbc.driver.OracleDriver";
    public final static String DbUrl = "jdbc:oracle:thin:@127.0.0.1:1521:orcl";
    public final static String User = "ufo";
    public final static String Pswd = "1234";
}

package com.ufo.bigsmall;

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;
import java.text.DecimalFormat;
import java.util.Random;
import java.util.Set;
import java.util.TreeSet;

import com.ufo.DBParam;

public class RecordChanger {
    public boolean changeOnePencent(String table) {
        Connection conn = null;
        Statement stmt = null;

        try{
            Class.forName(DBParam.Driver).newInstance();
            conn = DriverManager.getConnection(DBParam.DbUrl, DBParam.User, DBParam.Pswd);
            stmt = conn.createStatement();

            long startMs = System.currentTimeMillis();

            int totalCount=fetchExistCount(table,stmt);
            System.out.println("There are "+toEastNumFormat(totalCount)+" records in the table:'"+table+"'.");

            int changeCount=totalCount/100;
            System.out.println("There are "+toEastNumFormat(changeCount)+" records should be changed.");

            Set<Integer> idSet=fetchIdSet(totalCount,changeCount,table,stmt);
            System.out.println("There are "+toEastNumFormat(idSet.size())+" records in idSet.");

            int changed=updateRecords(idSet,table,stmt);
            System.out.println("There are "+toEastNumFormat(changed)+" records have been changed.");

            long endMs = System.currentTimeMillis();
            System.out.println("It takes "+ms2DHMS(startMs,endMs)+" to update 1% records of table:'"+table+"'.");
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            try {
                stmt.close();
                conn.close();
            } catch (SQLException e) {
                System.out.print("Can't close stmt/conn because of " + e.getMessage());
            }
        }

        return false;
    }

    private int updateRecords(Set<Integer> idSet,String tableName,Statement stmt)  throws SQLException{
        int updated=0;

        for(int id:idSet) {
            String sql="update "+tableName+" set name='"+getRNDName()+"' where id='"+id+"' ";
            updated+= stmt.executeUpdate(sql);
        }

        return updated;
    }

    private String getRNDName() {
        String[] arr= {"Andy","Bill","Cindy","张三","张飞","张好古","李四","王五","赵六","孙七","钱八","岳飞","关羽","刘备","曹操","张辽","虚竹","王语嫣"};
        int index=getRandom(0,arr.length);
        return arr[index];
    }

    // fetch a set of id which should be changed
    private Set<Integer> fetchIdSet(int totalCount,int changeCount,String tableName,Statement stmt)  throws SQLException{
        Set<Integer> idSet=new TreeSet<Integer>();

        while(idSet.size()<changeCount) {
            int id=getRandom(0,totalCount);
            if(idSet.contains(id)==false && isIdExist(id,tableName,stmt)) {
                idSet.add(id);
            }
        }

        return idSet;
    }

    private boolean isIdExist(int id,String tableName,Statement stmt)  throws SQLException{
        String sql="select count(*) as cnt from "+tableName+" where id='"+id+"' ";

        ResultSet rs = stmt.executeQuery(sql);

        while (rs.next()) {
            int cnt = rs.getInt("cnt");
            return cnt==1;
        }

        rs.close();
        return false;
    }

    // get a random num between min and max
    private static int getRandom(int min, int max){
        Random random = new Random();
        int s = random.nextInt(max) % (max - min + 1) + min;
        return s;
    }

    // fetch exist record count of a table
    private int fetchExistCount(String tableName,Statement stmt)  throws SQLException{
        String sql="select count(*) as cnt from "+tableName+"";

        ResultSet rs = stmt.executeQuery(sql);

        while (rs.next()) {
            int cnt = rs.getInt("cnt");
            return cnt;
        }

        rs.close();
        return 0;
    }

    // 将整数在万分位以逗号分隔表示
    public static String toEastNumFormat(long number) {
        DecimalFormat df = new DecimalFormat("#,####");
        return df.format(number);
    }

    // change seconds to DayHourMinuteSecond format
    private static String ms2DHMS(long startMs, long endMs) {
        String retval = null;
        long secondCount = (endMs - startMs) / 1000;
        String ms = (endMs - startMs) % 1000 + "ms";

        long days = secondCount / (60 * 60 * 24);
        long hours = (secondCount % (60 * 60 * 24)) / (60 * 60);
        long minutes = (secondCount % (60 * 60)) / 60;
        long seconds = secondCount % 60;

        if (days > 0) {
            retval = days + "d" + hours + "h" + minutes + "m" + seconds + "s";
        } else if (hours > 0) {
            retval = hours + "h" + minutes + "m" + seconds + "s";
        } else if (minutes > 0) {
            retval = minutes + "m" + seconds + "s";
        } else {
            retval = seconds + "s";
        }

        return retval + ms;
    }

    public static void main(String[] args) {
        RecordChanger rc=new RecordChanger();
        rc.changeOnePencent("bigtable");
    }
}

以下是修改两个表的运行结果反馈：

There are 10,0000 records in the table:'smalltable'.
There are 1000 records should be changed.
There are 1000 records in idSet.
There are 1000 records have been changed.
It takes 2s276ms to update 1% records of table:'smalltable'.

There are 100,0000 records in the table:'bigtable'.
There are 1,0000 records should be changed.
There are 1,0000 records in idSet.
There are 1,0000 records have been changed.
It takes 20s251ms to update 1% records of table:'bigtable'.

全部运行时间加起来一分钟出点头，还是可以的。

--END-- 2020年1月5日09点32分