Category：Database
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Time：2021-3-6
catalog Arrays and linked lists Linked list contrast summary 1. Arrays and linked lists Array: Array will open up a continuous space in memory to store data, which has both advantages and disadvantages. When obtaining data, the corresponding elements can be obtained directly through the subscript value, and the time complexity isO(1). But if you […]
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Time：2021-3-6
Basic concepts Streaming query means that after a successful query, it does not return a collection, but an iterator. The application gets a query result from the iterator each time. The advantage of streaming query is that it can reduce memory usage. If there is no streaming query, if we want to get 10 million […]
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Time：2021-3-6
Notes for novice when deploying dolphin DB 1. Why do Linux users have the error of “permission denied” when they start the control node or proxy node from the command line? For Linux users, before starting dolphin dB, you need to execute the following command to modify the permissions of executable files, enter the server […]
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Time：2021-3-6
Error reason: high version database (8.0) transfers SQL file and imports low version database (5.7) terms of settlement: Scheme 1: upgrade Mysql to a higher version Scheme 2: the SQL file to be imported, the utf8mb4_0900_ai_ciReplace all withutf8_general_ci utf8mb4Replace withutf8 Re execute SQL file
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Time：2021-3-6
<div style=”margin: 0px auto; color: rgb(85, 85, 85); max-width: 23cm; padding: 1em;”><div style=”margin: 0px; padding: 0px;”><div style=” padding:8px; “> < H3 style =” font family: & quot; Pt sans narrow & quot;, sans serif; font weight: 700; line height: 1.1em; color: rgb (133, 153, 0); font size: 1.4em; “> IO multithreading</h3> <p>In the past, redis […]
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Time：2021-3-6
preface The main contents of this paper are as follows*What is mongodbInstallation and configuration of mongodb4.0 in WindowsWe will focus on some problems encountered in the installation and configuration of mongodb4.0 in windows* What is mongodb Mongodb features summary: distributed file storage, easy to expand, unstructured Mongodb is a database based on distributed file storage. […]
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Time：2021-3-6
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Time：2021-3-5
Introduction of storage engine Database storage engine is the underlying software organization of database. Database management system (DBMS) creates, queries, modifies and deletes data through data engine. Different storage engines provide different storage mechanism, indexing skills, locking level and other functions. Using different storage engines, you can also obtain specific database functions. As the supporting […]
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Time：2021-3-5
It’s not honest to print a SQL abstract When mybatis starts SQL printing, it does not splice parameters into SQL statements, which brings great inconvenience to local development Mybatis plus completes the combination of SQL statements and parameters by collecting logs. Some ideas do not support this plug-in well As long as it is started […]
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Time：2021-3-5
[Abstract] as an excellent persistence layer framework, mybatis supports custom SQL, stored procedures and advanced mapping. 1、 Mybatis summary 1.mybatisIf the query / UPDATE statement fails to find a qualified record, what will be returned? If the return type is string, null is actually returned; The return type is object: null is actually returned; The […]
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Time：2021-3-5
1、 Brief introduction of Oracle timing task Oracle timing task is a very important subsystem in Oracle system. If it is used properly, it can greatly improve the operation and maintenance ability of our system. Oracle timing task function, you can execute the task at a specified point in time. So in practice, what kind […]
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Time：2021-3-5
preface This paper is the practice summary of redis cluster learning (based on redis 6.0 +). It introduces in detail the process of gradually building a redis cluster environment, and completes the practice of cluster scaling. Brief introduction of redis cluster Redis clusterIt is a distributed database solution provided by redisShardingTo share data, and provide […]
