RMAN的delete命令delete backupset 102;//删除102号备份集delete noprompt expired backup of tablespace xxwz_data;//无提示删
配置retention(保留)策略
不符合策略的备份集被标记为过期,,可查看可删除。
3种配置
rman>configure retention policy to后面可以加如下的3种方式:
1.recovery window of 7 days;时间窗口
保留恢复从今天开始往前7天的数据所需要保留的备份集
2.redundancy 2;冗余度
保留同一数据文件的2份备份集
3.none:手工
cross checking交叉检查:检查rman备份信息和实际是否同步
rman>list backup;
然后操作系统层面手工删除数据文件的备份集;
再次rman>list backup;依然可以查到已删除的备份集的信息;
rman>delete backupset 47;//删除该备份集时出错,说找不到该备份集。
rman>crosscheck backup;//检查
rman>list backup;//该备份集状态为过期。
obsolete VS expired
obsolete是不符合保留策略的状态,意为not needed。
expired是进行交叉检查时不找到的状态,意为not found。
RMAN的delete命令
delete backupset 102;//删除102号备份集
delete noprompt expired backup of tablespace xxwz_data;//无提示删除表空间的expired备份信息。
delete obsolete;//删除不需要的备份集
//备份时删除原来的备份
backup archivelog all delete input;
backup archivelog sequence between 99 and 199 thread 1 delete input;
修改RMAN的备份状态
rman>change backupset 49 unavailable;
rman>change backupset 49 available;
从保留策略中豁免(即不受保留策略的限制)
rman>change backupset 49 keep forever nologs;//永不限制
rman>change datafilecopy 'd:\copy\xxx.dbf' keep until 'sysdate+60';//不限制60天
catalog(登记)手动备份信息到RMAN存储里(可作为0级备份的基础)
登记数据文件
rman>catalog datafilecopy 'd:\backup\xxwz_data.dbf';
登记归档日志文件
rman>catalog archivelog 'd:\arch\arch_12.arc','d:\arch\arch_13.arc';
rman>catalog start with 'd:\arch' noprompt;//登记这个目录的所有归档日志文件信息
取消登记信息
rman>change backuppiece 51 uncatalog;
rman>change datafilecopy 'd:\backup\xxwz_data.dbf' uncatalog;
rman>change archivelog ... uncatalog

InnoDB uses redologs and undologs to ensure data consistency and reliability. 1.redologs record data page modification to ensure crash recovery and transaction persistence. 2.undologs records the original data value and supports transaction rollback and MVCC.

Key metrics for EXPLAIN commands include type, key, rows, and Extra. 1) The type reflects the access type of the query. The higher the value, the higher the efficiency, such as const is better than ALL. 2) The key displays the index used, and NULL indicates no index. 3) rows estimates the number of scanned rows, affecting query performance. 4) Extra provides additional information, such as Usingfilesort prompts that it needs to be optimized.

Usingtemporary indicates that the need to create temporary tables in MySQL queries, which are commonly found in ORDERBY using DISTINCT, GROUPBY, or non-indexed columns. You can avoid the occurrence of indexes and rewrite queries and improve query performance. Specifically, when Usingtemporary appears in EXPLAIN output, it means that MySQL needs to create temporary tables to handle queries. This usually occurs when: 1) deduplication or grouping when using DISTINCT or GROUPBY; 2) sort when ORDERBY contains non-index columns; 3) use complex subquery or join operations. Optimization methods include: 1) ORDERBY and GROUPB

MySQL/InnoDB supports four transaction isolation levels: ReadUncommitted, ReadCommitted, RepeatableRead and Serializable. 1.ReadUncommitted allows reading of uncommitted data, which may cause dirty reading. 2. ReadCommitted avoids dirty reading, but non-repeatable reading may occur. 3.RepeatableRead is the default level, avoiding dirty reading and non-repeatable reading, but phantom reading may occur. 4. Serializable avoids all concurrency problems but reduces concurrency. Choosing the appropriate isolation level requires balancing data consistency and performance requirements.

MySQL is suitable for web applications and content management systems and is popular for its open source, high performance and ease of use. 1) Compared with PostgreSQL, MySQL performs better in simple queries and high concurrent read operations. 2) Compared with Oracle, MySQL is more popular among small and medium-sized enterprises because of its open source and low cost. 3) Compared with Microsoft SQL Server, MySQL is more suitable for cross-platform applications. 4) Unlike MongoDB, MySQL is more suitable for structured data and transaction processing.

MySQL index cardinality has a significant impact on query performance: 1. High cardinality index can more effectively narrow the data range and improve query efficiency; 2. Low cardinality index may lead to full table scanning and reduce query performance; 3. In joint index, high cardinality sequences should be placed in front to optimize query.

The MySQL learning path includes basic knowledge, core concepts, usage examples, and optimization techniques. 1) Understand basic concepts such as tables, rows, columns, and SQL queries. 2) Learn the definition, working principles and advantages of MySQL. 3) Master basic CRUD operations and advanced usage, such as indexes and stored procedures. 4) Familiar with common error debugging and performance optimization suggestions, such as rational use of indexes and optimization queries. Through these steps, you will have a full grasp of the use and optimization of MySQL.

MySQL's real-world applications include basic database design and complex query optimization. 1) Basic usage: used to store and manage user data, such as inserting, querying, updating and deleting user information. 2) Advanced usage: Handle complex business logic, such as order and inventory management of e-commerce platforms. 3) Performance optimization: Improve performance by rationally using indexes, partition tables and query caches.


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