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  How expensive is a MySQL query?

Database access speed is always the bottle neck of many applications. Many application have large amount of data to search, retrieve and display nowadays. How do we improve the performance of our applications, how do we reduce the cost of database access? Apart from the design of database, the quality of the query is also one important factor to take care.  But before that, we need to know how much network traffic a query will consume. Yunyang,Zhang from Nubee in Singapore did some research...

   MySQL,Network traffic,Query     2013-04-09 05:13:33

  Python SSH Connection Tools

Program Design Purpose: We aim to create a simple Python SSH tool library that facilitates SSH communication, SCP file transfer, and SSH port forwarding through multiple jump hosts in an SSH tunnel chain. The library is designed to provide a simple API for establishing nested SSH tunnel connections through multiple jump hosts with customizable TCP ports. This allows users or their programs to automate SSH tasks such as: Batch processing SSH connection tasks, such as connecting to multiple ser...

       2024-08-30 04:46:05

  Python and PLC Communication

This article provides detailed steps on how to use Python to communicate with Schneider M221 and Siemens S7-1200 PLCs via Ethernet. Additionally, we offer a packaged Python PLC client library, enabling you to easily build your own SCADA control programs, such as Human-Machine Interfaces (HMI). The system overview is shown below: To check the project detail please refer to Python Physical PLC Communication Clients # Created: 2024/06/29 # Version: v0.1.3 # Copyright: Copyright (c) 2024 ...

   PYTHON,PLC,COMMUNICATION     2024-06-30 02:21:17

  2D Indoor CQB Robot Simulation

Program Design Purpose: The integration of robots in Close Quarters Battle (CQB) represents a significant advancement in modern military and law enforcement tactics. These robots, designed to navigate tight spaces, gather real-time intelligence, and engage threats, are invaluable assets in high-stakes scenarios. Our goal is to develop a 2D tactical board simulation system, similar to a computer game, that can load building floor blueprints, display CQB squad (robot) positions, enemy locations, ...

       2024-08-11 08:40:31

  4 deployment modes of Redis

As a high-performance in-memory database, Redis is widely used in current mainstream distributed architecture systems. To improve system fault tolerance, using multiple instances of Redis is also inevitable, but the complexity is much higher than that of a single instance. This article mainly introduces the four deployment modes of Redis and their advantages and disadvantages. Standalone Standalone mode is to install a Redis, start it, and business connects to it and that's all. The specific ...

   REDIS,STANDALONE,MASTER-SLAVE,SENTINEL,CLUSTER     2023-03-03 21:35:09

  Go是一门面向对象的编程语言吗

Golang已经开源了13年，在最近的TIOBE编程语言排名中，于2023年3月再次进入前十名，并比2022年底的排名上升了两个位置。 Go在2022年底提高了2个排名 许多第一次接触Go的开发者来自面向对象的编程语言，比如Java、Ruby等，他们在学习Go后第一个问题通常是：Go是一种面向对象的语言吗？在本文中，我们将探讨这个问题。 追溯 在广为人知的Go编程语言“圣经”《The Go Programming ...

   OOP,CHINESE,GOLANG,GO     2023-05-02 23:41:38

  Install and configure git plugin in Eclipse

When developing using IDE, it's always a good experience if everything can be done in the IDE including development, testing and version control. This also applies to Eclipse.  In this post, we will show the process of installing and configuring git plugin in Eclipse. The pre-requisite is that you have git installed on your local machine.  The detailed steps for installing and configuring git plugin are below. 1. Installing Git plugin Install using "Install New Software..." menu. ...

   ECLIPSE,GITHUB,GIT PLUGIN     2018-10-13 04:22:06

  The four key figures behind the success of JavaScript - Douglas Crockford

JavaScript's success can be attributed to at least four key figures: Brendan Eich, the creator of JavaScript Douglas Crockford, the creator of JSLint and JSON John Resig, the creator of jQuery Ryan Dahl, the creator of Node.js. We are already very familiar with Brendan Eich and the invention process of JavaScript, so let's start with Douglas Crockford, the second in command of JavaScript. Alliance In the 1990s, Microsoft's dominance overshadowed the whole world. At this time, two challengers e...

   JAVASCRIPT,DOUGLAS CROCKFORD,HISTORY     2023-05-07 06:42:30

  Fix SSL 'alert protocol version' issue while git clone remote repository

Git provides ways to securely connect to remote repository and clone remote repository to local machine. This post will teach you how to fix the "SSL23_GET_SERVER_HELLO:tlsv1 alert protocol version" issue while cloning a remote repository. The issue would look like: If this error occurs, it is most probably caused by out of date git version being used.To improve its security awareness, some weak cryptographic algorithms have been disabled and all git clients should upgrade to latest ones to acc...

   GIT,GIT CLONE,GIT SECURITY     2018-07-08 05:41:39

  Why (offset, limit) is slow in database select?

Starting from a problem Five years ago when I was working at Tencent, I found that MySQL request speed was very slow in the pagination scenario. With only 100,000 data, a select query on a single machine took about 2-3 seconds. I asked my mentor why, and he asked in return, "In an indexing scenario, what is the time complexity to get the nth largest number in MySQL?" The pursuit of the answer Confirming the scenario Assuming there is an index on the "status" column, a query like "select * from t...

   SLOW,LIMIT,OFFSET,MYSQL     2023-03-12 05:21:02

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