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Introduction Many coder s use database transactions without understanding the principle of transactions or even the basic concepts. It is very easy to make mistakes and write some code that they can't control. Many articles on the Internet are either concepts, a little source code, or a little test verification, which are not enough to fully u ...

Redis distributed lock Redis is a single process and single thread mode. The queue mode is adopted to change concurrent access into serial access, and there is no competition between multiple clients for redis connection. In redis, SETNX command can be used to realize distributed locking. If and only if the key does not exist, set the val ...

Previously, we learned the design rules of relational database: Follow the ER model and three paradigms (E entity represents the meaning of entity, corresponding to a table in the database; R relationship represents the meaning of relationship.)Three paradigms: 1 Column cannot be disassembled 2 Unique identification3 The relationship refer ...

Dynamic SQL Official documents: https://mybatis.net.cn/dynamic-sql.html What is dynamic SQL: dynamic SQL refers to generating different SQL statements according to different query conditions. The SQL statements we wrote before are relatively simple. If there are complex businesses, we need to write complex SQL statements, which often ne ...

Reverse crawler 14 Mongo introduction 1, The difference between MongoDB and MySQL MongoDB is a non relational database, which stores any form of json format data; MySQL is a relational database, which can only store table data with pre-defined fields. The following is a comparison of different data names between MongoDB and mysql. MySQLMongo ...

1. TCC of distributed transaction solution 1.1 what is a TCC transaction TCC is the abbreviation of try, Confirm and Cancel. TCC requires each branch transaction to implement three operations: preprocess try, Confirm and Cancel. Try performs business check and resource reservation, Confirm performs business confirmation, and Cancel imp ...

1.Elasticsearch related concepts There are several basic concepts in elastic search, such as node, index, document, etc., which are described below. Understanding these concepts is helpful for getting familiar with Elasticsearch Nodes and clusters Elasticsearch is essentially a distributed database that allows multiple servers to work togeth ...

9.1 migrate the data of the original CM node to the new node 9.1.1 backup the original CM node data It mainly backs up the monitoring data and management information of CM. The data directory includes: /var/lib/cloudera-host-monitor /var/lib/cloudera-service-monitor /var/lib/cloudera-scm-server /var/lib/cloudera-scm-eventserver /var/lib/clou ...

1. Understand the principle of MySQL master-slave replication. Mainly based on MySQL Binary log It mainly includes three threads (2 threads) I/O Threads, 1 individual SQL Thread) 1 , MySQL Record the data changes in the binary log; 2 , Slave take MySQL Copy binary lo ...

preface Hello, I'm sailing. We may not be very familiar with the registry, because we usually use less; However, it is the core of Windows. Many software startup and logging are included in it. It can be said that it is a large database. Today, let's take a look at how Python operates the registry.   1, Registration form first meeting Ther ...