scholl concepts

The data model is an abstract model in which objective things in the real world are interconnected.(1) A data Model is a set of integrated concepts that users describe and manipulate data within an organization, the relationships between data, and constraints on data, which contain data structures, operations, and integrity constraints(2) The conceptual model is also known as the entity-contact (E-R) model, which is mainly used to describe the relatio

favorite word is "everything has the price". Any performance gains we get through indexing are not without a price. The cost comes from several aspects.1. The principle of the clustered index we know that when the table is indexed, the data is stored as a B-tree. So when the update is inserted and deleted, it is necessary to move the page physically to adjust the B-tree. Therefore, when the update is inserted to delete data, it can degrade performance. For clustered indexes, when the table is u

This article mainly introduces the related concepts of data backup and recoverybackup : A copy of the stored data;Raw data: continuous change;Restore : Apply the Copy to the online system;Only the data status can be restored to the time of backup operation;Point-in- time recovery : Using binary logs to achieve time-based recovery;Why backup ?Disaster recovery: Hardware failure (redundancy, only when hardware is unavailable, service is available), soft

Learning the database so long, these concepts are still very vague, and today again, hope not to forget Three-level mode structure: External mode, mode, and internal modeFirst, schema (schema)Definition: Also known as logical mode, is a description of the logical structure and characteristics of all the data in the database, and is the public data view of all users.Understand:① a database has only one schema;② is the view of database data at the log

Tags: SQL databaseDefinedData Warehouse , which holds the data . is a file system , but also the use of files to save data , but access to data ( increase Delete modify query ) You must use a standard SQL statement to accessA common relational database*oracle-- large-scale applications, for a fee. *mysql--A small database, free open source! acquired by Oracle and charged from the 6.x version. *sqlserver-- Microsoft*DB2--IBM 's company, the bank's business. Related

In the 21st century, mankind entered the "Information Explosion era", a large number of data, information constantly produced, along with how to secure, efficient storage, retrieval and management of them. The use of databases enables efficient storage of data, efficient access, easy sharing, and security control.The need to use a databaseUsing a database enables efficient and well-organized storage of data, enabling people to manage data more quickly and easily. The database has the following c

Tags: regular pre-binary span binary between varchar bin positive A. Basic database Concepts I. Database: A collection of table and database Access objects, where the table stores different entity information, and each row of data corresponds to an entity's descriptive information I. Entities and records: 1entities are all things that are objective and can be described.2. Records: Data tables stored in the database, each "row" actually corresponds to

Let's start by talking about the two basic concepts of a database: Instance (Oracle Instance): an instance is a collection of Oracle background processes (referred to as UNIX systems)/threads (Windows systems) and a shared memory area (referred to as the SGA), a means of implementing access to the database, In other words, Oracle uses instances to give users access to the database Database: Refers to a set of files on the opera

MongoDB Basic concepts and common commandsMongo DB is currently in ITa non-relational database (NOSQL) that is popular in the industry, and its flexible data storage methods are favored by current it practitioners. Mongo DB is a good implementation of object-oriented thinking (Oo idea), in Mongo db each record is a document object. The biggest advantage of Mongo DB is that all data persistence requires no developers to write SQL statements manually,

entire document under the shell.DateThe JavaScript Date object is used as a type of MongoDB, and when a new Date object is created, it is usually called New Data ("").Basic conceptsThe following will be in accordance with the learning Rdms first introduce similar lines, tables, database concepts of knowledge, and then to learn to add or delete changes and other operations.1. DocumentationA document is a basic unit of data in MongoDB (similar to a row

Tags: construction part sof hidden unit identification von Neumann why commandin this chapter, we begin the introduction of Linux system, we first understand the structure of the disk and the concept of file system, in the foundation of the previous article, the main introduction of the use of Linux commands and other concepts, knowledge is trivial, I hope that these basic knowledge can be consolidated, alas ... Life is difficult, it is hard to learn.

1.2 Different types of replicationNow that you have completely understood the limitations of physics and theory, you can start learning different types of replication.1.2.1 Synchronous and asynchronous replicationThe first distinction we can make is the difference between synchronous replication and asynchronous replication.What does that mean? Suppose we have two servers and want to replicate data from one server (the master) to the second server (the slave). Describes the

Tags: abstract family concept technology share strong processor picture mil INFAbstract concepts of the operating system Files: Abstraction of I/O devices Virtual Memory: Abstraction of main memory and disk I/O devices Process: Abstraction of processor, main memory, and I/O devices Virtual Memory: Provides an illusion for a process The memory that each process sees is consistent, called the virtual address space.

; updating of variables) {Loop body}Steps:Initialization of the ① variable② condition judgment, if the condition is satisfied to execute the loop body, and then into the ③, if the condition is not met, the loop is terminated③ variable update, enter ②2.while Cyclewhile (condition) {Loop body (statement that contains a variable update)}3.do while loopdo{Loop body (statement that contains a variable update)}while (condition);The difference between a while and a do{}while loop: the latter is execute

register are the user stack address, the user stack is used, and when the process is in kernel space, the contents of the CPU stack pointer register are the kernel stack space address, using the kernel stack. When a process falls into a kernel state because of an outage or a system call, the stack used by the process goes from the user stack to the kernel stack.Single Core and micro coreThe operating system kernel may be a microkernel or a single kernel (the latter is sometimes referred to as t

the file systemMNT system Administrator installs the temporary file system installation pointPlacement of optional application packages that opt for additional installationProc virtual file system, storing the current memory mappingRoot Super User directorySbin Store binary executable files, only root to accessTMP is used to store various temporary filesUSR for storing system applications, more important directories /usr/local local Administrator software installation directoryvar is used to st

://s3.51cto.com/wyfs02/M01/73/50/wKioL1X6RbrRnCi_AAAd0YMH_XE939.gif "title=" loader _menu.gif "alt=" Wkiol1x6rbrrnci_aaad0ymh_xe939.gif "/>The Bootloder is installed in 1.MBR and provides a menu that can be directly directed to Linux.2. The bootloader that points to Windows is installed in partition 1.3. Partition 2 installs a bootloader that points to Linux.Attention:If you install Windows after installing Linux, Windows installs two copies of Bootloader in the MBR and the bootsector of its own

the address space has been exhausted, so the physical address 0x40000000 later memory can not be accessed.High-end Memory mapping method (mapped using 128M of memory linear address space)1. Permanent kernel mapping (void *kmp (struct page*page)High-end memory and low-end memory are availableThe kernel specifically leaves a linear space for this, from Pkmap_base to Fixaddr_start, to map high-end memory. On the 2.6 kernel, this address range is 4g-8m to 4g-4m. This space is called the "kernel per

language than to consider a compiled or interpreted language, and what is the real need for a project to make the development process easier and faster to develop, or to improve execution efficiency. The first place to design JavaScript is to make the development process easier.Five, Dynamic language1, JavaScript is a dynamic language, single from the point of view of the code, dynamic language variables and functions are not specified return value type.Vi. prototype-based object-oriented1, the

a class, the class class where the inner class resides is called an external class. A Features of the Inner class: Stand-alone class file also need to compile can also produce objects B Static Inner class:Definition method: Class outer{Static Class inner{Static inner classes cannot access external members unless the external member is also a static member}}Static inner classes Create objects: a. With an external class. B. Importing the package containing the inner Class C.