正如你所知,有时候我们有必要终止所有的Oracle过程(process)或者指定的一组Oracle过程。当数据库ldquo;锁定rdquo;而你无法进
正如你所知,有时候我们有必要终止所有的Oracle过程(process)或者指定的一组Oracle过程。当数据库“锁定”而你无法进入Server Manager来“温柔”的终止数据库时,就可以用UNIX中的kill命令来终止所有的Oracle过程——这是kill命令的常见用途之一。
当你需要终止一个UNIX服务器上的一个Oracle实例(instance)时,执行下面的步骤:
终止与ORACLE_SID有关的所有Oracle过程。
用ipcs –pmb命令来识别所有占用的RAM内存片断。
用ipcrm -m 命令来从UNIX中释放占用的RAM内存。
只对Non-AIX:用ipcs -sa命令来显示占用标记,,用ipcrm –s命令来释放该实例的占用标记。
创建单一命令来终止与挂起(hung)的数据库实例有关的Oracle过程是很简单的。在下面的例子之中,我们用ps指令来识别Oracle过程,然后用 awk程序来获取Oracle过程的过程ID(process ID,PID)。然后,我们把过程ID输入到UNIX的kill命令之中。
root> ps -ef|grep ora_| \
grep -v grep|awk '{print $2}'|xargs -i kill -9 {}
在终止所有Oracle过程之后,我们可以用ipcs –pmb指令来检查占用的内存并清除数据库所占用的内存。我们首先显示出数据库服务器上所有占用内存:
root> ipcs -pmb
IPC status from /dev/kmem as of Mon Sep 10 16:45:16 2001
T ID KEY MODE OWNER GROUP SEGSZ CPID LPID
Shared Memory:
m 24064 0x4cb0be18 --rw-r----- oracle dba 28975104 1836 23847
m 1 0x4e040002 --rw-rw-rw- root root 31008 572 572
m 2 0x411ca945 --rw-rw-rw- root root 8192 572 584
m 4611 0x0c6629c9 --rw-r----- root root 7216716 1346 23981
m 4 0x06347849 --rw-rw-rw- root root 77384 1346 1361
在这里,我们看到Oracle只拥有一个ID=24064的RAM内存。下面的命令将会释放这个内存片断:
root> ipcrm -m 24064

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.


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

AI Hentai Generator
Generate AI Hentai for free.

Hot Article

Hot Tools

Dreamweaver Mac version
Visual web development tools

SublimeText3 English version
Recommended: Win version, supports code prompts!

Notepad++7.3.1
Easy-to-use and free code editor

Atom editor mac version download
The most popular open source editor

SAP NetWeaver Server Adapter for Eclipse
Integrate Eclipse with SAP NetWeaver application server.