uuid | 易学教程

How unique are the ids generated with CFUUID , in iOS?

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问题 The title is my question actually. Now that Apple doesnt allow any more the use of UUID i decided to go with the CFUUID. However i have some questions regarding it. Is is unique for every device? If yes how is it different from UUID? Is it a random generator? If yes how good is it? Can i be sure that in 10000 devices there wont be a duplicate? I am between in this solution of using CFUUID , and having my server generating a random unique identifier that i can be sure of. However this would

How can I uniquely identify a git repository

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问题 I would like to create a tool that checks if I already have a local clone of a remote repository before cloning said repository. To do this, I need a way of testing if B is the same as repository A -- by which I guess i mean they have mergeable histories. B might be named differently than A, and might have additional branches -- the usual use cases. Is there a way to do this? I have a tentative idea how to do it, but I thought perhaps someone here has a definitive answer. Tentative idea Get a

Linux磁盘管理

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df命令 1.查看文件系统硬盘使用情况,linux硬盘不能直接使用必须有挂载点。 2.df -h 是适当的显示磁盘的单位 3.df -i 查看磁盘inode信息，inode满了，即使磁盘有空间也写不进去 du命令 1.查看一个目录或文件大小，为什么用ls 和 du 查看文件的大小不一样呢。　因为磁盘存储有一个块儿的概念，最小块儿是4k，不满足4k的也按4k。磁盘分区 1.查看磁盘命令，还可以给磁盘分区 fdisk -l 把系统中有的磁盘列出来 2.如果新插入了硬盘需要reboot重启主机 3.重启机器后可以看到新加的磁盘显示出来了。 4.fdisk /dev/sdb 给磁盘分区 5.-n 新建分区 -p 打印分区表 -d 删除分区 p 建立主分区 l 逻辑分区 6.主分区建立成功 7,逻辑分区从sdb5开始，逻辑分区一定是连续的，sdb5 6 7 磁盘格式化(只有格式化的分区才能被挂载) 1.center os支持的文件系统格式 cat /etc/filesystems 2.mount 命令查看磁盘是什么系统 / 和 boot 都是xfs [root@bogon ~]# mount|grep 'xfs' /dev/mapper/centos-root on / type xfs (rw,relatime,seclabel,attr2,inode64,noquota)

UUID to unique integer id?

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问题 I was wondering what the easiest way to convert a UUID to a unique integer would be? I have tried using the hash code but people tell me that it is not going to always be unique if i use the hash code? So what is the easiest way? Is the hash code unique? 回答1: You are going to have a problem since the UUID is 128 bits and the int is only 32bit. You'll either have to accept the risk of collisions and try to fudge it to a smaller space ( hashCode is probably a good way to do that) or find an

How to identify unique user?

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问题 Question How can you determine if a user is unique or not? I understand there are many ways to do this using cookies, but what about methods that don't use cookies? For example, go to Urban Dictionary and click one of the up/down vote buttons. Even if you delete your cookies and come back to the page, you will not be allowed to cast a vote on the same definition. How do they do this? Purpose Eventually, I'd like to use this unique user detection method on a site where users create accounts.

UUID versus auto increment number for primary key

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问题 Why should I choose UUID over an auto increment number for my entity's primary key? What are the pros and cons? 回答1: Andrey and Mjg both had good points, but I would add a related performance issue that is significant. With the decoupling of database and key generation also allows applications that have complex relationships between objects to create them all with the keys in place, so that bulk inserts are possible. In the case of auto-increment, all of the objects that own relationships (ie

How to get uuid or mac address from client in Java?

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问题 I'm looking for a solution for a Java based webapplication to uniquely identify the client. The server is in the same network as the clients and I thought that using the MAC address would be a good solution. The problem is I can't work with cookies because they can be deleted client-side and I can't use the IP because they could just issue a new DHCP lease renewal. So I would like to fallback to the MAC address of the clients. I'm aware that there is no java built in feature to get the MAC

PHP/MySQL: Storing and retrieving UUIDS

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问题 I'm trying to add UUIDs to a couple of tables, but I'm not sure what the best way to store/retrieve these would be. I understand it's far more efficient to use BINARY(16) instead of VARCHAR(36). After doing a bit of research, I also found that you can convert a UUID string to binary with: UNHEX(REPLACE(UUID(),'-','')) Pardon my ignorance, but is there an easy way to this with PHP and then turn it back to a string, when needed, for readability? Also, would it make much difference if I used

What namespace does the JDK use to generate a UUID with nameUUIDFromBytes?

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问题 The Sun/Oracle JDK exposes a function to create a type 3 (name based) UUID in the java.util package: java.util.UUID.nameUUIDFromBytes(byte[] name). I need to be able to generate a type 3 UUID in Java using nameUUIDFromBytes and arrive at the same UUID when creating a type 3 UUID in another language, assuming I provide the same bytes as the source. According to the javadocs this function creates a RFC 4122 compliant type 3 UUID. However, according to the RFC 4122 spec, a type 3 UUID must be

Type of Character generated by UUID

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问题 Does java.util.UUID generates special characters? What are the type of each character (eg- Uppercase, lower case, digits) generated by UUID. 回答1: UUID ≠ text To clarify, a UUID is actually a 128-bit value , not text or digits. You could think of them as 128-bit unsigned integers. Hex string Humans don't do well reading and writing 128 bits as 128 1 and 0 characters. When a UUID needs to be written for human consumption, we use a base-16 Hexadecimal (digits 0 - 9 and letters a - f ) string. We