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This question already has an answer here: PHP expects T_PAAMAYIM_NEKUDOTAYIM? 8 answers What's the story behind the :: 's sometimes token name T_PAAMAYIM_NEKUDOTAYIM I'm mainly interested in knowing if This is an abbreviation for something else. This is a phrase in a language other than English, and if so what's the language and what's a rough translation. This is some obscure-to-me programming term. Drunk developers. From the PHP docs : Paamayim Nekudotayim would, at first, seem like a strange choice for naming a double-colon. However, while writing the Zend Engine 0.5 (which powers PHP 3),

I'm very curious about old programming languages, especially COBOL, and as Wikipedia couldn't really tell me much about this topic, I decided to ask it here: Was COBOL the first programming language really being used in financial, stock and banking systems? Where exactly was COBOL used? Was it used more frequently than Fortran or BASIC, for example? I don't know if you lived at that time, but how did people react to the rising COBOL? Did they expect it to be the future? When has COBOL actually stopped being used to create new, big systems? Are you sure that there are still important legacy

当需要从数据库查询的表有上万条记录的时候，一次性查询所有结果会变得很慢，特别是随着数据量的增加特别明显，这时需要使用分页查询。对于数据库分页查询，也有很多种方法和优化的点。下面简单说一下我知道的一些方法。 准备工作 为了对下面列举的一些优化进行测试，下面针对已有的一张表进行说明。 1、表名：order_history 2、描述：某个业务的订单历史表 3、主要字段：unsigned int id，tinyint(4) int type 4、字段情况：该表一共37个字段，不包含text等大型数据，最大为varchar(500)，id字段为索引，且为递增。5、数据量：5709294 6、MySQL版本：5.7.16 线下找一张百万级的测试表可不容易，如果需要自己测试的话，可以写shell脚本什么的插入数据进行测试。 以下的 sql 所有语句执行的环境没有发生改变，下面是基本测试结果： select count(*) from orders_history; 返回结果：5709294 三次查询时间分别为： 8903 ms 8323 ms 8401 ms 一般分页查询 一般的分页查询使用简单的 limit 子句就可以实现。limit 子句声明如下： select * from table LIMIT [offset,] rows | rows OFFSET offset LIMIT

According to Bjarne Stroustrup, references were introduced into C++ to support operator overloading: References were introduced primarily to support operator overloading. C passes every function argument by value, and where passing an object by value would be inefficient or inappropriate the user can pass a pointer. This strategy doesn't work where operator overloading is used. In that case, notational convenience is essential because users cannot be expected to insert address-of operators if the objects are large. For example: a = b - c; is acceptable (that is, conventional) notation, but a =

【From】 https://blog.csdn.net/u013332124/article/details/88350345 Spark History Server 是spark内置的一个http服务，通过sbin/sbin/start-history-server.sh启动。History Server启动后，会监听一个端口，同时启动两个定时任务线程，分别用来解析eventLog日志文件和清理过期的eventLog日志文件。 Spark History Server启动后，我们可以直接在浏览器输入 http://ip:port 访问。一般默认端口是18080 一、eventLog日志文件以及相关参数 eventLog日志文件介绍 eventLog需要将配置spark.eventLog.enabled设置为true来开启，默认是关闭的。 开启这个配置后，当我们提交spark job到集群中运行时，之后spark job在运行过程中会不断的一些运行信息写到相关的日志文件中。具体的eventLog存放目录由配置spark.eventLog.dir决定的。 Spark job在运行中，会调用EventLoggingListener#logEvent()来输出eventLog内容。spark代码中定义了各种类型的事件，一旦某个事件触发，就会构造一个类型的Event

Why is it sensible for a language to allow implicit declarations of functions and typeless variables? I get that C is old, but allowing to omit declarations and default to int() (or int in case of variables) doesn't seem so sane to me, even back then. So, why was it originally introduced? Was it ever really useful? Is it actually (still) used? Note: I realise that modern compilers give you warnings (depending on which flags you pass them), and you can suppress this feature. That's not the question! Example: int main() { static bar = 7; // defaults to "int bar" return foo(bar); // defaults to a

hash 模式 这里的 hash 就是指 url 后的 # 号以及后面的字符 。比如说 " www.baidu.com/#hashhash " ，其中 "#hashhash" 就是我们期望的 hash 值。 由于 hash 值的变化不会导致浏览器像服务器发送请求，而且 hash 的改变会触发 hashchange 事件，浏览器的前进后退也能对其进行控制，所以在 H5 的 history 模式出现之前，基本都是使用 hash 模式来实现前端路由。 history 模式 利用了 HTML5 History 中新增的 pushState() 和 replaceState() 方法，这两个方法可以添加和修改历史记录条。只是当它们执行修改时，虽然改变了当前的 URL，但浏览器不会立即向服务器发送请求。 history.pushState() 和 history.replaceState() 均接收三个参数（state, title, url） 参数说明如下： state：合法的 Javascript 对象，可以用在 popstate 事件中 title：现在大多浏览器忽略这个参数，可以直接用 null 代替 url：任意有效的 URL，用于更新浏览器的地址栏 history.pushState() 和 history.replaceState() 的区别在于： history

Can someone explain how Eclipse's local history works? I accidentally overwrote a file in a project but need to revert to an earlier version. Is there a chance that Eclipse has the older file cached somewhere? To complete CurtainDog's answer: from eclipse FAQ Every time you modify a file in Eclipse, a copy of the old contents is kept in the local history. At any time, you can compare or replace a file with any older version from the history. Although this is no replacement for a real code repository, it can help you out when you change or delete a file by accident. Local history also has an

inux和unix上都提供了history命令，可以查询以前执行的命令历史记录 但是，这个记录并不包含时间项目 因此只能看到命令，但是不知道什么时间执行的 以下便是history记录时间的方法： 第一步：查看系统是否支持 注：本方法只对bash-3.0以上版本有效 执行rpm -q bash即可显示bash的版本 [root@localhost ~]# rpm -q bash bash-4.2.46-20.el7_2.x86_64 可见我系统中的bash版本没有问题 第二步：以root用户编辑/etc/bashrc文件，加入如下内容 HISTFILESIZE=2000 HISTSIZE=2000 HISTTIMEFORMAT="%Y%m%d-%H%M%S: " 或者 HISTTIMEFORMAT="%Y%m%d %T " vim /etc/bashrc HISTFILESIZE=5000 HISTSIZE=5000 HISTTIMEFORMAT="%Y%m%d-%H%M%S: " 执行生效 命令： export HISTTIMEFORMAT [root@localhost ~]# export HISTTIMEFORMAT 注：以上方法，也可以使用以下一条语句执行： echo "HISTFILESIZE=5000" >> /etc/bashrc && echo "HISTSIZE