undo受到redo的保护,以便历经前滚后在buffer cache中得到undo,并将这些undo运用到buffer cache里的数据块和索引块上,使那些数
1) redo和undo的“藕断丝连”
前滚redo
回滚undo
undo受到redo的保护,以便历经前滚后在buffer cache中得到undo,并将这些undo运用到buffer cache里的数据块和索引块上,使那些数据文件能“赶上”数据库的其余部分,从而保持数据库的一致性。
二者是DBA和开发人员的桥梁
回滚过程绝不涉及重做日志,只有恢复和归档时会读取重做日志。因为,重做日志是用来写的,而不是用来读!
2) 删除联机重做日志文件组的注意事项
①日志组为active和current状态时不可以删除
②日志组在数据库级别删除后操作系统上的文件不会被级链删除
③对于一个Oracle数据库实例,至少要包含两个联机重做日志组
3) redo buffer由谁来写入?
> redo buffer的写入 也是 lgwr吗?
No. Server (shadow) processes write to log buffer. LGWR writes redo records from the log buffer to the log file.
> 而undo buffer因为就是在db cache buffer,所以也是DBWR读入的吗?
Not quite sure what you mean. "Undo buffer" is just a buffer in buffer cache that corresponds to a block in an undo tablespace.
Treat it like any other data block. It's written into buffer cache by a server process and written out to datafiles by DBWn.
> 涉及IO(特别是异步),就需要一个专门的进程来完成
A server process can always read datafiles. But normally only DBWn can write to them. Also remember a server process can read and write a tempfile

MySQL is suitable for beginners to learn database skills. 1. Install MySQL server and client tools. 2. Understand basic SQL queries, such as SELECT. 3. Master data operations: create tables, insert, update, and delete data. 4. Learn advanced skills: subquery and window functions. 5. Debugging and optimization: Check syntax, use indexes, avoid SELECT*, and use LIMIT.

MySQL efficiently manages structured data through table structure and SQL query, and implements inter-table relationships through foreign keys. 1. Define the data format and type when creating a table. 2. Use foreign keys to establish relationships between tables. 3. Improve performance through indexing and query optimization. 4. Regularly backup and monitor databases to ensure data security and performance optimization.

MySQL is an open source relational database management system that is widely used in Web development. Its key features include: 1. Supports multiple storage engines, such as InnoDB and MyISAM, suitable for different scenarios; 2. Provides master-slave replication functions to facilitate load balancing and data backup; 3. Improve query efficiency through query optimization and index use.

SQL is used to interact with MySQL database to realize data addition, deletion, modification, inspection and database design. 1) SQL performs data operations through SELECT, INSERT, UPDATE, DELETE statements; 2) Use CREATE, ALTER, DROP statements for database design and management; 3) Complex queries and data analysis are implemented through SQL to improve business decision-making efficiency.

The basic operations of MySQL include creating databases, tables, and using SQL to perform CRUD operations on data. 1. Create a database: CREATEDATABASEmy_first_db; 2. Create a table: CREATETABLEbooks(idINTAUTO_INCREMENTPRIMARYKEY, titleVARCHAR(100)NOTNULL, authorVARCHAR(100)NOTNULL, published_yearINT); 3. Insert data: INSERTINTObooks(title, author, published_year)VA

The main role of MySQL in web applications is to store and manage data. 1.MySQL efficiently processes user information, product catalogs, transaction records and other data. 2. Through SQL query, developers can extract information from the database to generate dynamic content. 3.MySQL works based on the client-server model to ensure acceptable query speed.

The steps to build a MySQL database include: 1. Create a database and table, 2. Insert data, and 3. Conduct queries. First, use the CREATEDATABASE and CREATETABLE statements to create the database and table, then use the INSERTINTO statement to insert the data, and finally use the SELECT statement to query the data.

MySQL is suitable for beginners because it is easy to use and powerful. 1.MySQL is a relational database, and uses SQL for CRUD operations. 2. It is simple to install and requires the root user password to be configured. 3. Use INSERT, UPDATE, DELETE, and SELECT to perform data operations. 4. ORDERBY, WHERE and JOIN can be used for complex queries. 5. Debugging requires checking the syntax and use EXPLAIN to analyze the query. 6. Optimization suggestions include using indexes, choosing the right data type and good programming habits.


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