uuid

一、自建yum仓库，分别为网络源和本地源 [root@centos7 ~]# cd /etc/yum.repos.d/ [root@centos7 yum.repos.d]# mkdir bak #建立备份文件夹 [root@centos7 yum.repos.d]# mv *.repo bak/ #将系统自带yum仓库备份 [root@centos7 yum.repos.d]# vim base.repo #新建仓库文件 [root@centos7 yum.repos.d]# cat base.repo [development] #本地光盘yum源 name=dvdbase repo baseurl=file:///mnt/cdrom/ enabled=1 gpgcheck=1 gpgkey=file:///mnt/cdrom/RPM-GPG-KEY-CentOS-7 [aliyun] #阿里云yum源 name=aliyun repo baseurl=https://mirrors.aliyun.com/centos/$releasever/os/$basearch/ enabled=1 gpgchedk=1 gpgkey=https://mirrors.aliyun.com/centos/$releasever/os/$basearch/RPM-GPG-KEY-CentOS

分库分表之后，ID 主键如何处理？ 面试题 分库分表之后，id 主键如何处理？ 面试官心理分析 其实这是分库分表之后你必然要面对的一个问题，就是 id 咋生成？因为要是分成多个表之后，每个表都是从 1 开始累加，那肯定不对啊，需要一个 全局唯一 的 id 来支持。所以这都是你实际生产环境中必须考虑的问题。 面试题剖析 基于数据库的实现方案 数据库自增 id 这个就是说你的系统里每次得到一个 id，都是往一个库的一个表里插入一条没什么业务含义的数据，然后获取一个数据库自增的一个 id。拿到这个 id 之后再往对应的分库分表里去写入。 这个方案的好处就是方便简单，谁都会用； 缺点就是单库生成 自增 id，要是高并发的话，就会有瓶颈的；如果你硬是要改进一下，那么就专门开一个服务出来，这个服务每次就拿到当前 id 最大值，然后自己递增几个 id，一次性返回一批 id，然后再把当前最大 id 值修改成递增几个 id 之后的一个值；但是 无论如何都是基于单个数据库 。 适合的场景 ：你分库分表就俩原因，要不就是单库并发太高，要不就是单库数据量太大；除非是你 并发不高，但是数据量太大 导致的分库分表扩容，你可以用这个方案，因为可能每秒最高并发最多就几百，那么就走单独的一个库和表生成自增主键即可。 设置数据库 sequence 或者表自增字段步长 可以通过设置数据库 sequence

Have following CF: create column family gr_ip2 with column_type = 'Standard' and comparator = 'TimeUUIDType(reversed=true)' ...; then do following code: $uuid1 = phpcassa\UUID::uuid1(null, $time); $cf->insert("$key" , array($uuid1 => $url) ); it works without exceptions, but CF at the end is empty. $uuid1 is not string, but an object. When we do $cf->insert("$key" , array($uuid1 => $url) ); the object is converted to string, and insert fails. phpcassa does not give exeption, but insert fails anyway. Seems like we need to use ARRAY_FORMAT, so the object not to be "flatten" to string, $uuid1 =

The app I have found online works flawlessly except when clicking onto the Send Button, after typing something into the textbox, the printer runs, and stops in the middle of the process of printing, program doesn't crash however. I'm just curious if I'm using the wrong UUID, in fact I don't even know what it is. I have this following class, which is the only class needed to run the app, the rest are XML, with all three bluetooth permissions; package com.example.bluetoothprinter; import android.app.Activity; import android.bluetooth.BluetoothAdapter; import android.bluetooth.BluetoothDevice;

why should I use an app to generate UUID instead using database id's? is there an advantage? I see many apps that generates UUID preventing colision. so than is this possible to happen in database id like mysql or mongodb? One theoretical reason for using random UUIDs instead of relying on database IDs is the ability to do parallel inserts of new records without locking and incrementing a counter, or even looking up a unique index. If you have an auto-increment field, something needs to maintain this counter. The only way you can guarantee that the auto-increment facility will work correctly