RAC cache fusion机制实现原理分析
本文将详细介绍RAC cache fusion机制实现原理，需要了解更多的朋友可以参考下
在单实例中，进程要想修改数据块，必须在数据块的当前版本（Currentcopy）上进行修改RAC环境也一样这便涉及到一系列问题：
如何获得数据块的版本在集群节点间的分布图？
如何知道哪个节点拥有的是当前版本？
如何完成传递过程？
这一系列问题的解决依靠内存融合技术（cachefusion）
cachefusion通过高速的privateinterconnect，在实例间进行数据块传递
这是RAC最核心的工作机制，他把所有实例的SGA虚拟成一个大的SGA区
每当不同的实例请求相同的数据块，这个数据块就需要在实例间进行传递
在Oracle7的OPS中，这种传递是通过磁盘完成的，也叫“Disk-BasedPing”
也就是第1个实例必须先把这个数据块写回磁盘，然后第2个实例再从磁盘上读取这个数据块
这种依靠磁盘来完成数据传递极大影响系统性能
在Oracle8i引入“Net-BasedPing”通过PrivateInterconnect来传递数据块
但是8i只能传递没有修改过的数据块，对于“脏块”还是要通过磁盘来传递，这一点和OPS一样
在Oracle9i的cachefusion，所有的数据块，无论修改的或者没有修改的，都可以通过PrivateInterconnect传递
系统系能得到极大的改善
在cachefusion中，每个数据块都会被映射成一个cachefusion资源，或者说是一个PCM资源
PCM资源实际上是一个数据结构，资源的名称就是DBA(数据块地址)
每个进程对数据的请求都是分步完成：
①把DBA转换成PCM资源名称
②把这个PCM资源请求提交给DLM（分布式锁管理器）
③DLM进行GlobalLock的申请、释放活动，只有进程获得了PCMLock，才能继续下一步
也就是实例首先要获得数据块的使用权
整个cachefusion有两个服务组成：GCS和GES
⑴GCS服务负责数据块在实例间的传递
由后台进程LMSn完成
⑵GES服务负责锁管理
在多个实例之间协调对数据块的访问顺序，保证数据的一致性访问
由后台进程LMD完成
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
When might a full table scan be faster than using an index in MySQL?
Apr 09, 2025 am 12:05 AM
Full table scanning may be faster in MySQL than using indexes. Specific cases include: 1) the data volume is small; 2) when the query returns a large amount of data; 3) when the index column is not highly selective; 4) when the complex query. By analyzing query plans, optimizing indexes, avoiding over-index and regularly maintaining tables, you can make the best choices in practical applications.
Can I install mysql on Windows 7
Apr 08, 2025 pm 03:21 PM
Yes, MySQL can be installed on Windows 7, and although Microsoft has stopped supporting Windows 7, MySQL is still compatible with it. However, the following points should be noted during the installation process: Download the MySQL installer for Windows. Select the appropriate version of MySQL (community or enterprise). Select the appropriate installation directory and character set during the installation process. Set the root user password and keep it properly. Connect to the database for testing. Note the compatibility and security issues on Windows 7, and it is recommended to upgrade to a supported operating system.
Explain InnoDB Full-Text Search capabilities.
Apr 02, 2025 pm 06:09 PM
InnoDB's full-text search capabilities are very powerful, which can significantly improve database query efficiency and ability to process large amounts of text data. 1) InnoDB implements full-text search through inverted indexing, supporting basic and advanced search queries. 2) Use MATCH and AGAINST keywords to search, support Boolean mode and phrase search. 3) Optimization methods include using word segmentation technology, periodic rebuilding of indexes and adjusting cache size to improve performance and accuracy.
Difference between clustered index and non-clustered index (secondary index) in InnoDB.
Apr 02, 2025 pm 06:25 PM
The difference between clustered index and non-clustered index is: 1. Clustered index stores data rows in the index structure, which is suitable for querying by primary key and range. 2. The non-clustered index stores index key values and pointers to data rows, and is suitable for non-primary key column queries.
MySQL: Simple Concepts for Easy Learning
Apr 10, 2025 am 09:29 AM
MySQL is an open source relational database management system. 1) Create database and tables: Use the CREATEDATABASE and CREATETABLE commands. 2) Basic operations: INSERT, UPDATE, DELETE and SELECT. 3) Advanced operations: JOIN, subquery and transaction processing. 4) Debugging skills: Check syntax, data type and permissions. 5) Optimization suggestions: Use indexes, avoid SELECT* and use transactions.
Explain different types of MySQL indexes (B-Tree, Hash, Full-text, Spatial).
Apr 02, 2025 pm 07:05 PM
MySQL supports four index types: B-Tree, Hash, Full-text, and Spatial. 1.B-Tree index is suitable for equal value search, range query and sorting. 2. Hash index is suitable for equal value searches, but does not support range query and sorting. 3. Full-text index is used for full-text search and is suitable for processing large amounts of text data. 4. Spatial index is used for geospatial data query and is suitable for GIS applications.
The relationship between mysql user and database
Apr 08, 2025 pm 07:15 PM
In MySQL database, the relationship between the user and the database is defined by permissions and tables. The user has a username and password to access the database. Permissions are granted through the GRANT command, while the table is created by the CREATE TABLE command. To establish a relationship between a user and a database, you need to create a database, create a user, and then grant permissions.
Can mysql and mariadb coexist
Apr 08, 2025 pm 02:27 PM
MySQL and MariaDB can coexist, but need to be configured with caution. The key is to allocate different port numbers and data directories to each database, and adjust parameters such as memory allocation and cache size. Connection pooling, application configuration, and version differences also need to be considered and need to be carefully tested and planned to avoid pitfalls. Running two databases simultaneously can cause performance problems in situations where resources are limited.
