理解redo（5）深入学习RBA
RBA就是redo entries在重做日志文件中所对应的地址。定义：块第一次变脏时所对应的redo entries在redo log file里的位置CKPT-Q按
1 定义
RBA就是redo entries在重做日志文件中所对应的地址
2 组成
RBA由三部分组成：
序列号（4个字节)
块号(4个字节）
起始字节（2个字节）
以上都是16进制存储
3 类型
3.1 LRBA
定义：块第一次变脏时所对应的redo entries在redo log file里的位置
注释：CKPT-Q按LRBA的顺序维护脏块，执行检查点事件时，DBWn从CKPT-Q按LRBA的顺序写出。LRBA也就是checkpoint position。从检查点位置（LRBA)处，，应用重做记录到On disk rba处，这个过程就是前滚。
3.2 HRBA
定义：脏块在buffer cache中最近一次被更新时产生的redo entries在redo log file里的位置
注释：如果HRBA > on-disk RABA，那么HRBA所对应的相关redo entries还在redo log buffer中，如果实例crash，则HRBA是不可能被恢复的。
3.3 checkpoint RBA
定义：在CKPT-Q上第一个脏数据块的LRBA,这个RBA之前的脏数据已经被全部写入磁盘。
注释：当一个checkpoint事件发生的时候，CKPT进程会记录下当时所写的重做日志记录的地址（即RBA),此时记录的RBA被称之为checkpoint RBA,从上一个checkpoint RBA到当前checkpoint RBA之间的日志所保护的buffer cache中的脏块接下来将会被写进数据文件。
3.4 on-disk RBA
定义：LGWR 写日志文件的最末位置的地址，磁盘中重做日志文件的最后一条重做记录。
注释：on disk rba是Oracle前滚操作的终点。on disk 顾名思义 就是'在磁盘上'的意思.比这个更高的rba,都在log buffer中,还没有来的急被写进磁盘中的日志文件.所以是不能被用于恢复的。
3.5 target RBA
定义：检查点事件结束时的checkpoint RBA
注释：为了缩短实例恢复的时间，DBWn会尽力把checkpoint RBA的目标值定的长远点。
Hot AI Tools
Undresser.AI Undress
AI-powered app for creating realistic nude photos
AI Clothes Remover
Online AI tool for removing clothes from photos.
Undress AI Tool
Undress images for free
Clothoff.io
AI clothes remover
Video Face Swap
Swap faces in any video effortlessly with our completely free AI face swap tool!
Hot Article
Hot Tools
Notepad++7.3.1
Easy-to-use and free code editor
SublimeText3 Chinese version
Chinese version, very easy to use
Zend Studio 13.0.1
Powerful PHP integrated development environment
Dreamweaver CS6
Visual web development tools
SublimeText3 Mac version
God-level code editing software (SublimeText3)
Hot Topics
1387
52
How does Go language implement the addition, deletion, modification and query operations of the database?
Mar 27, 2024 pm 09:39 PM
Go language is an efficient, concise and easy-to-learn programming language. It is favored by developers because of its advantages in concurrent programming and network programming. In actual development, database operations are an indispensable part. This article will introduce how to use Go language to implement database addition, deletion, modification and query operations. In Go language, we usually use third-party libraries to operate databases, such as commonly used sql packages, gorm, etc. Here we take the sql package as an example to introduce how to implement the addition, deletion, modification and query operations of the database. Assume we are using a MySQL database.
iOS 18 adds a new 'Recovered' album function to retrieve lost or damaged photos
Jul 18, 2024 am 05:48 AM
Apple's latest releases of iOS18, iPadOS18 and macOS Sequoia systems have added an important feature to the Photos application, designed to help users easily recover photos and videos lost or damaged due to various reasons. The new feature introduces an album called "Recovered" in the Tools section of the Photos app that will automatically appear when a user has pictures or videos on their device that are not part of their photo library. The emergence of the "Recovered" album provides a solution for photos and videos lost due to database corruption, the camera application not saving to the photo library correctly, or a third-party application managing the photo library. Users only need a few simple steps
How does Hibernate implement polymorphic mapping?
Apr 17, 2024 pm 12:09 PM
Hibernate polymorphic mapping can map inherited classes to the database and provides the following mapping types: joined-subclass: Create a separate table for the subclass, including all columns of the parent class. table-per-class: Create a separate table for subclasses, containing only subclass-specific columns. union-subclass: similar to joined-subclass, but the parent class table unions all subclass columns.
An in-depth analysis of how HTML reads the database
Apr 09, 2024 pm 12:36 PM
HTML cannot read the database directly, but it can be achieved through JavaScript and AJAX. The steps include establishing a database connection, sending a query, processing the response, and updating the page. This article provides a practical example of using JavaScript, AJAX and PHP to read data from a MySQL database, showing how to dynamically display query results in an HTML page. This example uses XMLHttpRequest to establish a database connection, send a query and process the response, thereby filling data into page elements and realizing the function of HTML reading the database.
Detailed tutorial on establishing a database connection using MySQLi in PHP
Jun 04, 2024 pm 01:42 PM
How to use MySQLi to establish a database connection in PHP: Include MySQLi extension (require_once) Create connection function (functionconnect_to_db) Call connection function ($conn=connect_to_db()) Execute query ($result=$conn->query()) Close connection ( $conn->close())
How to handle database connection errors in PHP
Jun 05, 2024 pm 02:16 PM
To handle database connection errors in PHP, you can use the following steps: Use mysqli_connect_errno() to obtain the error code. Use mysqli_connect_error() to get the error message. By capturing and logging these error messages, database connection issues can be easily identified and resolved, ensuring the smooth running of your application.
Tips and practices for handling Chinese garbled characters in databases with PHP
Mar 27, 2024 pm 05:21 PM
PHP is a back-end programming language widely used in website development. It has powerful database operation functions and is often used to interact with databases such as MySQL. However, due to the complexity of Chinese character encoding, problems often arise when dealing with Chinese garbled characters in the database. This article will introduce the skills and practices of PHP in handling Chinese garbled characters in databases, including common causes of garbled characters, solutions and specific code examples. Common reasons for garbled characters are incorrect database character set settings: the correct character set needs to be selected when creating the database, such as utf8 or u
How to connect to remote database using Golang?
Jun 01, 2024 pm 08:31 PM
Through the Go standard library database/sql package, you can connect to remote databases such as MySQL, PostgreSQL or SQLite: create a connection string containing database connection information. Use the sql.Open() function to open a database connection. Perform database operations such as SQL queries and insert operations. Use defer to close the database connection to release resources.
