Programmer Group

First, the principle of interprocess communication Each process has its own user address space, and the global variables of any process can not be seen in another process. Therefore, the exchange of data between processes must open a buffer in the kernel through the kernel. Process 1 copies data from user space to the kernel buffer, and proce ...

This article describes how to start MongoDB and connect with a shell. Here are some of the operations we are familiar with in mysql 1. Create a database MongoDB The grammatical format for creating the database is as follows: ``` use DATABASE_NAME ``` //If the database does not exist, create the database, otherwise switch to the specified d ...

Cumulative Measures refer to aggregating data from the first element in the sequence to the current element, such as statistics of cumulative sales from January to the current month of each year. This article explains how to realize the cumulative monthly sales volume and amount in the sales order example, and makes corresponding modifications ...

1. Brief description When using HBase, if you have billions of rows or millions of columns of data, the ability to return a large amount of data in a query is subject to the bandwidth of the network, and even if the network conditions allow, the client's computing may not be able to meet the requirements.In this case, Coprocessors arise.It all ...

Shell variables2.1. What is a VariableIn elementary school, we learned mathematical equations, such as: what is y equal to when x = 1 and y = x + 1 are known? In the above topics x and y are called unknowns, but in shell programming they are variable names, and 1 on the right of the equal sign and x+1 are variable contents. "=" i ...

To illustrate the example below, we first install the Apache server and then start Apache. [root@localhost ~]# yum install httpd [root@localhost ~]# systemctl start httpd [root@localhost ~]# ps aux | grep http root 3716 0.5 0.0 221936 5000 ? Ss 13:49 0:00 /usr/sbin/httpd -DFOREGROUND apache 3717 0.0 0.0 224020 3088 ...

One Day Command-screen screenMultiple Terminal Window Manager, which allows you to connect multiple local or remote sessions simultaneously and switch freelyUse: screen [ -options ] [ cmd [ args ] ] screen -r [[pid.]tty[.host]] screen -r sessionowner/[[pid.]tty[.host]] -A&nbs ...

Several terms Ambiguity: When we write data to a pipe, such as a hello, when we write he, the reader already reads the data, so this is incorrect. This is ambiguity. Critical resource: A common storage resource accessible by multiple streams Critical Zones: Codes that access critical resources are called critical zones Mutual exclusion: Only ...

We propose two solutions for watermarking project 1. Implementation with shadow dom 1. Basic Ideas By attach Shadow, a shadow root node is generated, and then a watermarking is added under the root node through a circular statement. The position is used to layout the absolute and make it full of containers.  show me the code: (function (ro ...

This article belongs to a confused pig original, please indicate the source author.The two Demo addresses in this article are located at: https://github.com/ftc300/PythonAmazing.gitWelcome to follow and start.I'm an android developer, but I have to say that python also brings me fun and convenience. After last weekend's rain, Xuanwu Lake burne ...