在网上有一种短8位UUID生成的方法，代码来源：
JAVA生成短8位UUID
-
public static
String[] chars =
new
String[] {
"a",
"b",
"c",
"d",
"e",
"f",
-
"g",
"h",
"i",
"j",
"k",
"l",
"m",
"n",
"o",
"p",
"q",
"r",
"s",
-
"t",
"u",
"v",
"w",
"x",
"y",
"z",
"0",
"1",
"2",
"3",
"4",
"5",
-
"6",
"7",
"8",
"9",
"A",
"B",
"C",
"D",
"E",
"F",
"G",
"H",
"I",
-
"J",
"K",
"L",
"M",
"N",
"O",
"P",
"Q",
"R",
"S",
"T",
"U",
"V",
-
"W",
"X",
"Y",
"Z" };
-
-
-
public static
String generateShortUuid() {
-
StringBuffer shortBuffer =
new StringBuffer();
-
String uuid = UUID.randomUUID().toString().
replace(
"-",
"");
-
for (
int i =
0; i <
8; i++) {
-
String str = uuid.substring(i *
4, i *
4 +
4);
-
int x = Integer.parseInt(str,
16);
-
shortBuffer.append(chars[x %
0x3E]);
-
}
-
return shortBuffer.toString();
-
-
}
我们进行测试看到底多少会出现重复，写了一个比较简单的方法：
设置了线程池，数据库连接池，每一个线程进行处理一百万条数据，每次携带7万条数据进行数据库的插入。我们将ID设置为数据库的主键，如果出现错误，则表示数据库ID出现重复现象。
如果需要一次性插入更多的数据，或者在插入的时候报下面的错误：
Packet for query is too large (4,800,048 > 4,194,304)
-
修改 my.ini 加上 max_allowed_packet =
67108864
-
67108864=
64M
-
默认大小
4194304 也就是
4M
-
修改完成之后要重启mysql服务，如果通过命令行修改就不用重启mysql服务。
-
命令修改：
-
设置为
500M
-
mysql>
set
global max_allowed_packet =
500*
1024*
1024;
-
-
查看mysql的max_allowed_packet大小,运行
-
show VARIABLES
like
'%max_allowed_packet%';
下面是插入数据代码，进行测试：
-
private
static ThreadPoolExecutor threadPoolExecutor=
new ThreadPoolExecutor(
50,
100,
-
0L, TimeUnit.MILLISECONDS,
-
new LinkedBlockingQueue<Runnable>(
1024),
new DefaultManagedAwareThreadFactory(),
new ThreadPoolExecutor.AbortPolicy());
-
-
-
-
@Override
-
public void saveTest() {
-
threadPoolExecutor.execute(
new saveUUID());
-
}
-
/**
-
* 设置保存信息的线程
-
*/
-
class saveUUID implements Runnable{
-
public saveUUID(){
-
}
-
@Override
-
public void run() {
-
System.out.println(
"===================>>>>>" + Thread.currentThread().getName());
-
List<Map<String,Object>> userList =
new ArrayList<>();
-
int index=
0;
-
for(
int i =
0; i<
1000000;i++){
-
long startTime = System.currentTimeMillis();
-
Map<String,Object> map =
new HashMap<>();
-
map.put(
"id",getUUID8());
-
userList.add(map);
-
index++;
-
if (index==
70000) {
-
int count = testMapper.saveTest(userList);
-
if (count >
0) {
-
userList.clear();
-
index=
0;
-
long time =System.currentTimeMillis()-startTime;
-
System.out.println( Thread.currentThread().getName() +
"======>>>>" +time );
-
}
-
}
-
}
-
if(!userList.isEmpty()){
-
testMapper.saveTest(userList);
-
}
-
-
}
-
}
XML文件：
-
<insert id=
"saveTest" parameterType=
"java.util.List">
-
insert into tb_user(id,user_name)
-
values
-
<foreach item=
"item" index=
"index" collection=
"list" separator=
",">
-
(
#{item.id},#{item.id})
-
</
foreach>
-
</insert>
进行测试当数据达到：2129580，也就是两百万的时候出现第一次重复，进行数据库数据查询，发现重复原因是因为MySQL不区分大小写。
关于MySQL主键不区分大小写，或则其他查询不区分大小写 Duplicate entry 'AOVbrXXF' for key 'PRIMARY'
将MySQL进行大小写区分。再进行测试。
数据达到400万条无重复，系统插入缓慢。
在基础数据为0的情况下，插入数据100万。系统花费时间为：
26.318秒
在基础数据为0的情况下，插入数据200万。系统花费的时间为：
64.097秒
在基础数据为0的情况下，插入数据，系统花费时间：
-
DefaultManagedAwareThreadFactory-
1======
>>>>
3209
-
DefaultManagedAwareThreadFactory-
1======
>>>>
1033
-
DefaultManagedAwareThreadFactory-
1======
>>>>
1089
-
DefaultManagedAwareThreadFactory-
1======
>>>>
952
-
DefaultManagedAwareThreadFactory-
1======
>>>>
921
-
DefaultManagedAwareThreadFactory-
1======
>>>>
1119
-
DefaultManagedAwareThreadFactory-
1======
>>>>
825
-
DefaultManagedAwareThreadFactory-
1======
>>>>
911
-
DefaultManagedAwareThreadFactory-
1======
>>>>
919
-
DefaultManagedAwareThreadFactory-
1======
>>>>
850
-
DefaultManagedAwareThreadFactory-
1======
>>>>
949
-
DefaultManagedAwareThreadFactory-
1======
>>>>
983
-
DefaultManagedAwareThreadFactory-
1======
>>>>
720
-
DefaultManagedAwareThreadFactory-
1======
>>>>
1097
-
DefaultManagedAwareThreadFactory-
1======
>>>>
862
-
DefaultManagedAwareThreadFactory-
1======
>>>>
1173
-
DefaultManagedAwareThreadFactory-
1======
>>>>
942
-
DefaultManagedAwareThreadFactory-
1======
>>>>
808
-
DefaultManagedAwareThreadFactory-
1======
>>>>
1159
-
DefaultManagedAwareThreadFactory-
1======
>>>>
845
-
DefaultManagedAwareThreadFactory-
1======
>>>>
998
-
DefaultManagedAwareThreadFactory-
1======
>>>>
1478
-
DefaultManagedAwareThreadFactory-
1======
>>>>
1420
-
DefaultManagedAwareThreadFactory-
1======
>>>>
974
-
DefaultManagedAwareThreadFactory-
1======
>>>>
1398
-
DefaultManagedAwareThreadFactory-
1======
>>>>
4005
-
DefaultManagedAwareThreadFactory-
1======
>>>>
2922
-
DefaultManagedAwareThreadFactory-
1======
>>>>
2126
-
DefaultManagedAwareThreadFactory-
1======
>>>>
1198
-
DefaultManagedAwareThreadFactory-
1======
>>>>
931
-
DefaultManagedAwareThreadFactory-
1======
>>>>
2197
-
DefaultManagedAwareThreadFactory-
1======
>>>>
1014
-
DefaultManagedAwareThreadFactory-
1======
>>>>
1231
-
DefaultManagedAwareThreadFactory-
1======
>>>>
3416
-
DefaultManagedAwareThreadFactory-
1======
>>>>
4471
-
DefaultManagedAwareThreadFactory-
1======
>>>>
960
-
DefaultManagedAwareThreadFactory-
1======
>>>>
1199
-
DefaultManagedAwareThreadFactory-
1======
>>>>
1142
-
DefaultManagedAwareThreadFactory-
1======
>>>>
940
-
DefaultManagedAwareThreadFactory-
1======
>>>>
2211
-
DefaultManagedAwareThreadFactory-
1======
>>>>
23994
-
DefaultManagedAwareThreadFactory-
1======
>>>>
37751
-
DefaultManagedAwareThreadFactory-
1======
>>>>
51163
-
DefaultManagedAwareThreadFactory-
1======
>>>>
66993
-
DefaultManagedAwareThreadFactory-
1======
>>>>
79591
-
DefaultManagedAwareThreadFactory-
1======
>>>>
91846
由上可见当数据量达到一定量的时候，时间成指数上升。
如何能突破这个时间节点，估计还需要进一步优化。
生产UUID满足千万条数据
目前1147万条数据，没有出现重复，满足原作者说的千万条数据不重复
转载：https://blog.csdn.net/weixin_41986096/article/details/105579978
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