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发布时间:2008-05-22 10:19:25

doc上的原话,记录一下,感觉写的很精彩![@more@]Steps in The Oracle Performance Improvement MethodGet candid feedback from users. Determine the performance project's scope and subsequent performance goals, as well as performance goals for the future. This process is key in future capacity planning. Get a full set of operating system, database, and application statistics from the system when the performance is both good and bad. If these are not available, then get whatever is available. Missing s......【阅读全文】

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发布时间:2008-05-22 09:06:11

定位系统性能瓶颈的时候要多利用数据以及统计信息等资源而不要过多的依赖自己以前积累的经验想当然。因为今天的系统已经变的非常复杂,性能分析的一些浮浅的规则不容易产生。oracle性能改进方法论定义的是一种工作的方法而不是一组权威性的规则。在定位性能瓶颈的时候,最好的规则就是没有规则(With bottleneck detection, the only rule is that there are no rules!The best performance engineers use the data provided and think laterally to determine performance problems.)[@more@]The Oracle performance improvement method......【阅读全文】

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发布时间:2008-05-21 22:30:26

从下面的doc理解,如果单一的应用程序跑在oracle数据库服务器上,那么(On an Oracle data server system, where there is generally only one application running, the server runs database activity in user space. Activities required to service database requests (such as scheduling, synchronization, I/O, memory management, and process/thread creation and tear down) run in kernel mode. In a system where all CPU is fully utilized, a healthy Oracle system runs between 65% and 95% in user space.)oracle对系统......【阅读全文】

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发布时间:2008-05-21 07:43:42

http://space.itpub.net/756652/viewspace-244138转,不错的文章![@more@]http://space.itpub.net/756652/viewspace-244138......【阅读全文】

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发布时间:2008-05-19 13:06:55

http://www.itpub.net/thread-148366-1-2.html记录一下![@more@]http://www.itpub.net/thread-148366-1-2.html......【阅读全文】

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发布时间:2008-05-14 22:29:07

什么是Scalability,看看他的形容词的意思:scalable adj.可攀登的可升级的,这里Scalability我通常理解为系统的可攀升能力。doc的原意是:Scalability is a system's ability to process more workload, with a proportional increase in system resource usage. In other words, in a scalable system, if you double the workload, then the system would use twice as many system resources. This sounds obvious, but due to conflicts within the system, the resource usage might exceed twice the original workload.[@more@]Un......【阅读全文】

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发布时间:2008-05-14 22:23:50

不知道该起个什么样的标题来记录这句话,看到这句话时感觉写的非常好,想记录一下:Performance problems are usually the result of contention for, or exhaustion of, some system resource性能问题通常是一些系统资源被争夺或者是被耗尽的结果![@more@]Performance problems are usually the result of contention for, or exhaustion of, some system resource --===========================================从另外的角度来讲:性能问题来至于:Performance problems generally result from either a lack of throughput, unaccept......【阅读全文】

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发布时间:2008-05-07 22:49:33

What Is Disk Contention?Disk contention occurs when multiple processes try to access the same disk simultaneously. Most disks have limits on both the number of accesses (I/O operations each second) and the amount of data they can transfer each second (I/O data rate, or throughput). When these limits are reached, processes must wait to access the disk.[@more@]What Is Disk Contention?Disk contention occurs when multiple processes try to access the same disk simultaneously. Most disks have limits o......【阅读全文】

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发布时间:2008-05-07 22:13:47

http://www.itpub.net/thread-877110-1-5.html收藏记录一下![@more@]http://www.itpub.net/thread-877110-1-5.html......【阅读全文】

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发布时间:2008-05-06 13:00:02

Some pitfalls are discussed in the following sections:Hit ratios Wait events with timed statistics Comparing Oracle statistics with other factors Wait events without timed statistics Idle wait events Computed statistics [@more@]Interpreting StatisticsWhen initially examining performance data, you can formulate potential theories by examining your statistics. One way to ensure that your interpretation of the statistics is correct is to perform cross-checks with other data. This establishes whethe......【阅读全文】

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发布时间:2008-05-06 10:51:17

尽管oracle已经不建议使用SORT_AREA_SIZE参数了,oracle建议通过设置PGA_AGGREGATE_TARGET来激活自动工作区管理。不过在doc上看到了,随手记录一下![@more@]Specifying Memory for SQL Work Area with SORT_AREA_SIZEThe memory for the SQL work area can also be controlled with the SORT_AREA_SIZE initialization parameter.Note: Oracle does not recommend using the SORT_AREA_SIZE parameter unless the instance is configured with the shared server option. Oracle recommends that you enable automatic sizing of SQL wor......【阅读全文】

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发布时间:2008-05-06 09:44:28

创建同样大小的表空间,永久表空间要比临时标空间慢很多,原因就像doc所言创建数据文件时block需要被初始化为"empty",其实我觉得就是初始化成oracle可以识别的以db_block_size为大小的block格式吧;而临时文件不需要被初始化![@more@]During tablespace creation, the datafiles that make up the tablespace are initialized with special "empty" block images. TEMPFILES are not initialized.SQL> set timing onSQL> create tablespace test datafile 'C:APPWCHORADATADB11TEST01.DBF' SIZE 1G;表空间已创建......【阅读全文】

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发布时间:2008-05-04 10:10:49

需要注意的一句话是:Usually, the optimizer does not consider the order in which tables appear in the FROM clause when choosing an execution plan.[@more@]Choosing Execution Plans for Joins with the RBONote: The following considerations apply to both the cost-based and rule-based approaches:The optimizer first determines whether joining two or more of the tables definitely results in a row source containing at most one row. The optimizer recognizes such situations based on UNIQUE and PRIMARY KEY c......【阅读全文】

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发布时间:2008-05-03 22:06:53

下面列出来的这些条件都会执行Full Table Scan,因此我们在使用时要特别注意![@more@]RBO Path 15: Full Table ScanThis access path is available for any SQL statement, regardless of its WHERE clause conditions, except when its FROM clause contains SAMPLE or SAMPLE BLOCK.Note that the full table scan is the lowest ranked access path on the list. This means that the RBO always chooses an access path that uses an index if one is available, even if a full table scan might execute faster.The following cond......【阅读全文】

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发布时间:2008-05-02 23:58:58

If the WHERE clauses uses columns of many single-column indexes, then Oracle executes the statement by performing a range scan on each index to retrieve the rowids of the rows that satisfy each condition. Oracle then merges the sets of rowids to obtain a set of rowids of rows that satisfy all conditions. Oracle then accesses the table using these rowids.Oracle can merge up to five indexes. If the WHERE clause uses columns of more than five single-column indexes, then Oracle merges five of them, ......【阅读全文】

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发布时间:2008-05-02 23:29:47

当我第一次看到hint相关内容中讲到AND_EQUAL时(The AND_EQUAL hint explicitly chooses an execution plan that uses an access path that merges the scans on several single-column indexes.)感觉没有读懂,不知道这里提到的merge到底指的什么意思,但是当看到RBO Path 9: Single-Column Indexes章节中的解释时对AND_EQUAL已经非常清楚了,原来是对单列index scan找到满足条件的rowid的merge(If the WHERE clauses uses columns of many single-column indexes, then Oracle executes the statement by performing a range scan on ......【阅读全文】

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发布时间:2008-05-01 22:53:51

RBO Path 1: Single Row by RowidThis access path is available only if the statement's WHERE clause identifies the selected rows by rowid or with the CURRENT OF CURSOR embedded SQL syntax supported by the Oracle precompilers. To execute the statement, Oracle accesses the table by rowid.[@more@]验证1:This access path is available only if the statement's WHERE clause identifies the selected rows by rowidSQL> select tt.* , rowid from tt;ID NA ROWID---------- -- ------------------1 a AAAEG4AAEAAAA......【阅读全文】

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发布时间:2008-05-01 22:36:18

doc上的原话,随手记录下!Note that the full table scan is the lowest ranked access path on the list. This means that the RBO always chooses an access path that uses an index if one is available, even if a full table scan might execute faster.从上面这段话我们知道full table scan 是最低等级的访问路径,那意味着下面列出来的15种访问路径的数字越小等级越高,也就是说使用访问路径的等级越高rbo认为效率越高,当然实际情况可能并非如此。[@more@]Understanding Access Paths for the RBOUsing the RBO, the optimizer ......【阅读全文】

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