Tag:Detailed explanation

  • Basic usage analysis of MySQL performance optimization artifact explain

    Time:2021-3-9

    brief introduction MySQL provides an explain command, which can analyze the select statement and output the detailed information of select execution for developers to optimize The use of the explain command is very simple. Just add explain before the select statement EXPLAIN SELECT * from user_info WHERE id < 300; get ready In order to […]

  • Detailed explanation and example of Oracle temporary table

    Time:2020-9-17

    In Oracle 8i or above, you can create two types of temporary tables: 1。 Session specific temporary tables CREATE GLOBAL TEMPORARY <TABLE_NAME> ( <column specification> ) ON COMMIT PRESERVE ROWS;  2。 Transaction specific temporary tables CREATE GLOBAL TEMPORARY <TABLE_NAME> ( <column specification> ) ON COMMIT DELETE ROWS; CREATE GLOBAL TEMPORARY TABLE MyTempTable   Although the created […]

  • Detailed explanation of Rudy overload method

    Time:2020-5-27

    In a subclass, we can change the behavior of an entity by overloading its parent method ruby> class Human     |   def identify     |     print “I’m a person.\n”     |   end     |   def train_toll(age)     |     if age < 12     |       print “Reduced fare.\n”;     |     else     |       print “Normal fare.\n”;     |     end     |   end     | end    nil ruby> Human.new.identify I’m a person.    nil ruby> class Student1<Human     |   def identify     |     print “I’m a student.\n”     |   end     | end    nil ruby> Student1.new.identify I’m a student.    nil   If we just want to enhance the identity method of the parent class instead […]

  • 3 minutes to quickly learn how to use cookies in asp.net core MVC

    Time:2020-3-23

    1、 What is a cookie? My friend asked me what cookies are and what they are used for, but I couldn’t explain them clearly and briefly, which led me to ponder: why can’t I explain clearly, and I have doubts about the method of learning! So when we are learning something, we must know what […]

  • Redis tutorial (10): details of persistence

    Time:2020-2-21

    1、 What persistence mechanisms redis provides: 1). RDB persistence:This mechanism is to write the data set snapshot in memory to disk within a specified time interval.    2). AOF persistence:This mechanism will record every write operation processed by the server in the form of log. At the beginning of redis server startup, the file will be […]

  • PMAP command in Linux

    Time:2019-9-27

    By looking at the help, the following information was returned: Usage: pmap [options] pid [pid …] Options: -x, –extended show details -X show even more details WARNING: format changes according to /proc/PID/smaps -XX show everything the kernel provides -c, –read-rc read the default rc -C, –read-rc-from=<file> read the rc from file -n, –create-rc create new […]

  • FreeBSD Software Installation and Uninstallation Tools–Detailed Description of Ports and Packages

    Time:2019-9-3

    1. How to grab the tarball only?2. How can we only do the steps of unlocking the tarball?3. How to unlock the tarball and add the official patch?4. How to install a new port?5. How to install a new port and package it?6. How to package a port and all its dependent ports?7. How to […]

  • FreeBSD6.2 Setting up FTP Server

    Time:2019-8-30

    Two Modes of FTP OnlineFTP adopts Client/Server architecture. The special feature of FTP protocol is that it must establish two online systems when it is used: one for transmitting instructions and the other for transmitting files. When we use FTP software to connect to the FTP server, the client will first connect to port 21 […]

  • Detailed explanation of VI usage under BSD

    Time:2019-8-19

    VI usageVI command can be said to be the most commonly used command to edit files in the Unix/linux world, but because of its many command sets, many people are not accustomed to using it. In fact, you only need to master the basic commands, and then use them flexibly, you will find its advantages, […]

  • Detailed Hibernate mapping configuration

    Time:2019-8-11

    Detailed Hibernate mapping configuration Each hibernate will only introduce a file at startup: hibernate. cfg. XML Mapping requires us to introduce it into hibernate. <mapping resource=”com/hibernate/test/hibernate_IP.xml”/> <mapping/> Code snippet: <?xml version=”1.0″?> <!DOCTYPE hibernate-mapping PUBLIC “-//Hibernate/Hibernate Mapping DTD 3.0//EN” “http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd”> <hibernate-mapping package=”com.hibernate.test”> <class name=”IP_List” table=”IP_LIST”> <id name=”ip” column=”Ip”> <generator></generator> </id> <property name=”Status” column=”Status”></property> </class> </hibernate-mapping> The […]

  • Oracle AWR (Automatic Workload Archives) Management and Maintenance Details

    Time:2019-8-6

    Preface AWR is short for Automatic Workload Repository, which is called Automatic Workload Repository in Chinese. For AWR management, mainly for snapshot and baseline management. For example, set the snapshot interval, delete the snapshot, set the snapshot retention time. For baselines, that is baseline creation, deletion, automatic creation, etc. This paper mainly describes the contents […]

  • Use of Index and Explain in MongoDB Database

    Time:2019-6-20

    Preface This article mainly introduces the relevant contents about index and explanation in MongoDB, and shares them for your reference and study. Let’s have a look at the detailed introduction. Mongodb index usage Effect Indexes can usually greatly improve queries. An index is a data structure that collects the values of a specific field of […]