Oracle数据库性能模型

悠悠 2022-08-07 10:39 201阅读 0赞

## Oracle数据库性能模型 ##

最近一直在思考一个问题：**如何为一个数据库建立性能模型**？作为一名DBA来说，我们面临的一个巨大挑战是：如何保证数据库的性能可以满足快速变化的应用的需求，如何在数据量和访问量持续增长的情况下，保证应用的响应时间和数据库的负载处在合理的水平下。我们可能会经常面对以下的问题：某个SQL每秒要执行100次，响应时间是多少？某个应用发布后，对数据库的影响如何？所以，评估应用对数据库所产生的影响，优化应用并预测风险，保证数据库的可用性和稳定性，这是应用DBA真正有价值的地方。

**响应时间为中心：**

如果要选择一个评价系统优劣的性能指标，毫无疑问应该是**响应时间**。响应时间是客户体验的第一要素，所有的优化都应该为降低响应时间而努力。对于数据库系统也是如此，我们优化系统，优化SQL，最终目标都是为了降低响应时间，单位时间内可以处理更多的请求。

**数据库时间模型：**

响应时间一般分为服务时间(Service time)和等待时间(Wait time)，服务时间指进程占用CPU的时间，包括前台进程(Server process)和后台进程(Backgroud process)，我们一般只关注前台进程占用的CPU time。等待时间包括很多类型，一般最常见的是IO等待和并发等待，IO等待包括sequential read，scattered read和log file sync等等，而并发等待主要是latch和enqueue。SQL execute elapsed time指用户进程执行SQL的响应时间，包含CPU time和wait time。

以下是Oracle数据库的时间模型：

[![Oracle\_Time\_Model][Oracle_Time_Model]][Oracle_Time_Model]

在Oracle系统中，我们可以利用AWR或Statspack报告，看到数据库的时间信息：

<table> 
 <tbody style="margin:0px;padding:0px;"> 
 <tr style="margin:0px;padding:0px;"> 
 <th style="margin:0px;padding-right:4px;padding-bottom:2px;padding-left:4px;border-left-style:dotted;border-left-color:rgb(255,255,255);border-right-style:dotted;border-right-color:rgb(255,255,255);border-bottom-color:rgb(255,255,255);vertical-align:middle;font-size:8pt;line-height:normal;font-family:Arial, Helvetica, Geneva, sans-serif;color:#FFFFFF;background-color:rgb(0,102,204);">Statistic Name</th> 
 <th style="margin:0px;padding-right:4px;padding-bottom:2px;padding-left:4px;border-left-style:dotted;border-left-color:rgb(255,255,255);border-right-style:dotted;border-right-color:rgb(255,255,255);border-bottom-color:rgb(255,255,255);vertical-align:middle;font-size:8pt;line-height:normal;font-family:Arial, Helvetica, Geneva, sans-serif;color:#FFFFFF;background-color:rgb(0,102,204);">Time (s)</th> 
 <th style="margin:0px;padding-right:4px;padding-bottom:2px;padding-left:4px;border-left-style:dotted;border-left-color:rgb(255,255,255);border-right-style:dotted;border-right-color:rgb(255,255,255);border-bottom-color:rgb(255,255,255);vertical-align:middle;font-size:8pt;line-height:normal;font-family:Arial, Helvetica, Geneva, sans-serif;color:#FFFFFF;background-color:rgb(0,102,204);">% of DB Time</th> 
 </tr> 
 <tr style="margin:0px;padding:0px;"> 
 <td style="margin:0px;border-left-style:dotted;border-left-color:rgb(255,255,255);border-right-style:dotted;border-right-color:rgb(255,255,255);border-bottom-color:rgb(255,255,255);vertical-align:top;font-size:8pt;line-height:normal;font-family:Arial, Helvetica, Geneva, sans-serif;color:#000000;background-color:rgb(255,255,204);">sql execute elapsed time</td> 
 <td align="right" style="margin:0px;border-left-style:dotted;border-left-color:rgb(255,255,255);border-right-style:dotted;border-right-color:rgb(255,255,255);border-bottom-color:rgb(255,255,255);vertical-align:top;font-size:8pt;line-height:normal;font-family:Arial, Helvetica, Geneva, sans-serif;color:#000000;background-color:rgb(255,255,204);">3,062.17</td> 
 <td align="right" style="margin:0px;border-left-style:dotted;border-left-color:rgb(255,255,255);border-right-style:dotted;border-right-color:rgb(255,255,255);border-bottom-color:rgb(255,255,255);vertical-align:top;font-size:8pt;line-height:normal;font-family:Arial, Helvetica, Geneva, sans-serif;color:#000000;background-color:rgb(255,255,204);">91.52</td> 
 </tr> 
 <tr style="margin:0px;padding:0px;"> 
 <td style="margin:0px;border-left-style:dotted;border-left-color:rgb(255,255,255);border-right-style:dotted;border-right-color:rgb(255,255,255);border-bottom-color:rgb(255,255,255);vertical-align:top;font-size:8pt;line-height:normal;font-family:Arial, Helvetica, Geneva, sans-serif;color:#000000;">DB CPU</td> 
 <td align="right" style="margin:0px;border-left-style:dotted;border-left-color:rgb(255,255,255);border-right-style:dotted;border-right-color:rgb(255,255,255);border-bottom-color:rgb(255,255,255);vertical-align:top;font-size:8pt;line-height:normal;font-family:Arial, Helvetica, Geneva, sans-serif;color:#000000;">2,842.08</td> 
 <td align="right" style="margin:0px;border-left-style:dotted;border-left-color:rgb(255,255,255);border-right-style:dotted;border-right-color:rgb(255,255,255);border-bottom-color:rgb(255,255,255);vertical-align:top;font-size:8pt;line-height:normal;font-family:Arial, Helvetica, Geneva, sans-serif;color:#000000;">84.95</td> 
 </tr> 
 <tr style="margin:0px;padding:0px;"> 
 <td style="margin:0px;border-left-style:dotted;border-left-color:rgb(255,255,255);border-right-style:dotted;border-right-color:rgb(255,255,255);border-bottom-color:rgb(255,255,255);vertical-align:top;font-size:8pt;line-height:normal;font-family:Arial, Helvetica, Geneva, sans-serif;color:#000000;background-color:rgb(255,255,204);">parse time elapsed</td> 
 <td align="right" style="margin:0px;border-left-style:dotted;border-left-color:rgb(255,255,255);border-right-style:dotted;border-right-color:rgb(255,255,255);border-bottom-color:rgb(255,255,255);vertical-align:top;font-size:8pt;line-height:normal;font-family:Arial, Helvetica, Geneva, sans-serif;color:#000000;background-color:rgb(255,255,204);">25.87</td> 
 <td align="right" style="margin:0px;border-left-style:dotted;border-left-color:rgb(255,255,255);border-right-style:dotted;border-right-color:rgb(255,255,255);border-bottom-color:rgb(255,255,255);vertical-align:top;font-size:8pt;line-height:normal;font-family:Arial, Helvetica, Geneva, sans-serif;color:#000000;background-color:rgb(255,255,204);">0.77</td> 
 </tr> 
 <tr style="margin:0px;padding:0px;"> 
 <td style="margin:0px;border-left-style:dotted;border-left-color:rgb(255,255,255);border-right-style:dotted;border-right-color:rgb(255,255,255);border-bottom-color:rgb(255,255,255);vertical-align:top;font-size:8pt;line-height:normal;font-family:Arial, Helvetica, Geneva, sans-serif;color:#000000;">PL/SQL execution elapsed time</td> 
 <td align="right" style="margin:0px;border-left-style:dotted;border-left-color:rgb(255,255,255);border-right-style:dotted;border-right-color:rgb(255,255,255);border-bottom-color:rgb(255,255,255);vertical-align:top;font-size:8pt;line-height:normal;font-family:Arial, Helvetica, Geneva, sans-serif;color:#000000;">11.75</td> 
 <td align="right" style="margin:0px;border-left-style:dotted;border-left-color:rgb(255,255,255);border-right-style:dotted;border-right-color:rgb(255,255,255);border-bottom-color:rgb(255,255,255);vertical-align:top;font-size:8pt;line-height:normal;font-family:Arial, Helvetica, Geneva, sans-serif;color:#000000;">0.35</td> 
 </tr> 
 <tr style="margin:0px;padding:0px;"> 
 <td style="margin:0px;border-left-style:dotted;border-left-color:rgb(255,255,255);border-right-style:dotted;border-right-color:rgb(255,255,255);border-bottom-color:rgb(255,255,255);vertical-align:top;font-size:8pt;line-height:normal;font-family:Arial, Helvetica, Geneva, sans-serif;color:#000000;background-color:rgb(255,255,204);">sequence load elapsed time</td> 
 <td align="right" style="margin:0px;border-left-style:dotted;border-left-color:rgb(255,255,255);border-right-style:dotted;border-right-color:rgb(255,255,255);border-bottom-color:rgb(255,255,255);vertical-align:top;font-size:8pt;line-height:normal;font-family:Arial, Helvetica, Geneva, sans-serif;color:#000000;background-color:rgb(255,255,204);">7.55</td> 
 <td align="right" style="margin:0px;border-left-style:dotted;border-left-color:rgb(255,255,255);border-right-style:dotted;border-right-color:rgb(255,255,255);border-bottom-color:rgb(255,255,255);vertical-align:top;font-size:8pt;line-height:normal;font-family:Arial, Helvetica, Geneva, sans-serif;color:#000000;background-color:rgb(255,255,204);">0.23</td> 
 </tr> 
 <tr style="margin:0px;padding:0px;"> 
 <td style="margin:0px;border-left-style:dotted;border-left-color:rgb(255,255,255);border-right-style:dotted;border-right-color:rgb(255,255,255);border-bottom-color:rgb(255,255,255);vertical-align:top;font-size:8pt;line-height:normal;font-family:Arial, Helvetica, Geneva, sans-serif;color:#000000;">hard parse elapsed time</td> 
 <td align="right" style="margin:0px;border-left-style:dotted;border-left-color:rgb(255,255,255);border-right-style:dotted;border-right-color:rgb(255,255,255);border-bottom-color:rgb(255,255,255);vertical-align:top;font-size:8pt;line-height:normal;font-family:Arial, Helvetica, Geneva, sans-serif;color:#000000;">5.06</td> 
 <td align="right" style="margin:0px;border-left-style:dotted;border-left-color:rgb(255,255,255);border-right-style:dotted;border-right-color:rgb(255,255,255);border-bottom-color:rgb(255,255,255);vertical-align:top;font-size:8pt;line-height:normal;font-family:Arial, Helvetica, Geneva, sans-serif;color:#000000;">0.15</td> 
 </tr> 
 <tr style="margin:0px;padding:0px;"> 
 <td style="margin:0px;border-left-style:dotted;border-left-color:rgb(255,255,255);border-right-style:dotted;border-right-color:rgb(255,255,255);border-bottom-color:rgb(255,255,255);vertical-align:top;font-size:8pt;line-height:normal;font-family:Arial, Helvetica, Geneva, sans-serif;color:#000000;background-color:rgb(255,255,204);">connection management call elapsed time</td> 
 <td align="right" style="margin:0px;border-left-style:dotted;border-left-color:rgb(255,255,255);border-right-style:dotted;border-right-color:rgb(255,255,255);border-bottom-color:rgb(255,255,255);vertical-align:top;font-size:8pt;line-height:normal;font-family:Arial, Helvetica, Geneva, sans-serif;color:#000000;background-color:rgb(255,255,204);">3.13</td> 
 <td align="right" style="margin:0px;border-left-style:dotted;border-left-color:rgb(255,255,255);border-right-style:dotted;border-right-color:rgb(255,255,255);border-bottom-color:rgb(255,255,255);vertical-align:top;font-size:8pt;line-height:normal;font-family:Arial, Helvetica, Geneva, sans-serif;color:#000000;background-color:rgb(255,255,204);">0.09</td> 
 </tr> 
 <tr style="margin:0px;padding:0px;"> 
 <td style="margin:0px;border-left-style:dotted;border-left-color:rgb(255,255,255);border-right-style:dotted;border-right-color:rgb(255,255,255);border-bottom-color:rgb(255,255,255);vertical-align:top;font-size:8pt;line-height:normal;font-family:Arial, Helvetica, Geneva, sans-serif;color:#000000;">hard parse (sharing criteria) elapsed time</td> 
 <td align="right" style="margin:0px;border-left-style:dotted;border-left-color:rgb(255,255,255);border-right-style:dotted;border-right-color:rgb(255,255,255);border-bottom-color:rgb(255,255,255);vertical-align:top;font-size:8pt;line-height:normal;font-family:Arial, Helvetica, Geneva, sans-serif;color:#000000;">0.04</td> 
 <td align="right" style="margin:0px;border-left-style:dotted;border-left-color:rgb(255,255,255);border-right-style:dotted;border-right-color:rgb(255,255,255);border-bottom-color:rgb(255,255,255);vertical-align:top;font-size:8pt;line-height:normal;font-family:Arial, Helvetica, Geneva, sans-serif;color:#000000;">0.00</td> 
 </tr> 
 <tr style="margin:0px;padding:0px;"> 
 <td style="margin:0px;border-left-style:dotted;border-left-color:rgb(255,255,255);border-right-style:dotted;border-right-color:rgb(255,255,255);border-bottom-color:rgb(255,255,255);vertical-align:top;font-size:8pt;line-height:normal;font-family:Arial, Helvetica, Geneva, sans-serif;color:#000000;background-color:rgb(255,255,204);">repeated bind elapsed time</td> 
 <td align="right" style="margin:0px;border-left-style:dotted;border-left-color:rgb(255,255,255);border-right-style:dotted;border-right-color:rgb(255,255,255);border-bottom-color:rgb(255,255,255);vertical-align:top;font-size:8pt;line-height:normal;font-family:Arial, Helvetica, Geneva, sans-serif;color:#000000;background-color:rgb(255,255,204);">0.01</td> 
 <td align="right" style="margin:0px;border-left-style:dotted;border-left-color:rgb(255,255,255);border-right-style:dotted;border-right-color:rgb(255,255,255);border-bottom-color:rgb(255,255,255);vertical-align:top;font-size:8pt;line-height:normal;font-family:Arial, Helvetica, Geneva, sans-serif;color:#000000;background-color:rgb(255,255,204);">0.00</td> 
 </tr> 
 <tr style="margin:0px;padding:0px;"> 
 <td style="margin:0px;border-left-style:dotted;border-left-color:rgb(255,255,255);border-right-style:dotted;border-right-color:rgb(255,255,255);border-bottom-color:rgb(255,255,255);vertical-align:top;font-size:8pt;line-height:normal;font-family:Arial, Helvetica, Geneva, sans-serif;color:#000000;">PL/SQL compilation elapsed time</td> 
 <td align="right" style="margin:0px;border-left-style:dotted;border-left-color:rgb(255,255,255);border-right-style:dotted;border-right-color:rgb(255,255,255);border-bottom-color:rgb(255,255,255);vertical-align:top;font-size:8pt;line-height:normal;font-family:Arial, Helvetica, Geneva, sans-serif;color:#000000;">0.00</td> 
 <td align="right" style="margin:0px;border-left-style:dotted;border-left-color:rgb(255,255,255);border-right-style:dotted;border-right-color:rgb(255,255,255);border-bottom-color:rgb(255,255,255);vertical-align:top;font-size:8pt;line-height:normal;font-family:Arial, Helvetica, Geneva, sans-serif;color:#000000;">0.00</td> 
 </tr> 
 <tr style="margin:0px;padding:0px;"> 
 <td style="margin:0px;border-left-style:dotted;border-left-color:rgb(255,255,255);border-right-style:dotted;border-right-color:rgb(255,255,255);border-bottom-color:rgb(255,255,255);vertical-align:top;font-size:8pt;line-height:normal;font-family:Arial, Helvetica, Geneva, sans-serif;color:#000000;background-color:rgb(255,255,204);">DB time</td> 
 <td align="right" style="margin:0px;border-left-style:dotted;border-left-color:rgb(255,255,255);border-right-style:dotted;border-right-color:rgb(255,255,255);border-bottom-color:rgb(255,255,255);vertical-align:top;font-size:8pt;line-height:normal;font-family:Arial, Helvetica, Geneva, sans-serif;color:#000000;background-color:rgb(255,255,204);">3,345.74</td> 
 <td align="right" style="margin:0px;border-left-style:dotted;border-left-color:rgb(255,255,255);border-right-style:dotted;border-right-color:rgb(255,255,255);border-bottom-color:rgb(255,255,255);vertical-align:top;font-size:8pt;line-height:normal;font-family:Arial, Helvetica, Geneva, sans-serif;color:#000000;background-color:rgb(255,255,204);"> </td> 
 </tr> 
 <tr style="margin:0px;padding:0px;"> 
 <td style="margin:0px;border-left-style:dotted;border-left-color:rgb(255,255,255);border-right-style:dotted;border-right-color:rgb(255,255,255);border-bottom-color:rgb(255,255,255);vertical-align:top;font-size:8pt;line-height:normal;font-family:Arial, Helvetica, Geneva, sans-serif;color:#000000;">background elapsed time</td> 
 <td align="right" style="margin:0px;border-left-style:dotted;border-left-color:rgb(255,255,255);border-right-style:dotted;border-right-color:rgb(255,255,255);border-bottom-color:rgb(255,255,255);vertical-align:top;font-size:8pt;line-height:normal;font-family:Arial, Helvetica, Geneva, sans-serif;color:#000000;">204.91</td> 
 <td align="right" style="margin:0px;border-left-style:dotted;border-left-color:rgb(255,255,255);border-right-style:dotted;border-right-color:rgb(255,255,255);border-bottom-color:rgb(255,255,255);vertical-align:top;font-size:8pt;line-height:normal;font-family:Arial, Helvetica, Geneva, sans-serif;color:#000000;"> </td> 
 </tr> 
 <tr style="margin:0px;padding:0px;"> 
 <td style="margin:0px;border-left-style:dotted;border-left-color:rgb(255,255,255);border-right-style:dotted;border-right-color:rgb(255,255,255);border-bottom-color:rgb(255,255,255);vertical-align:top;font-size:8pt;line-height:normal;font-family:Arial, Helvetica, Geneva, sans-serif;color:#000000;background-color:rgb(255,255,204);">background cpu time</td> 
 <td align="right" style="margin:0px;border-left-style:dotted;border-left-color:rgb(255,255,255);border-right-style:dotted;border-right-color:rgb(255,255,255);border-bottom-color:rgb(255,255,255);vertical-align:top;font-size:8pt;line-height:normal;font-family:Arial, Helvetica, Geneva, sans-serif;color:#000000;background-color:rgb(255,255,204);">72.30</td> 
 <td align="right" style="margin:0px;border-left-style:dotted;border-left-color:rgb(255,255,255);border-right-style:dotted;border-right-color:rgb(255,255,255);border-bottom-color:rgb(255,255,255);vertical-align:top;font-size:8pt;line-height:normal;font-family:Arial, Helvetica, Geneva, sans-serif;color:#000000;background-color:rgb(255,255,204);"> </td> 
 </tr> 
 </tbody> 
</table>

DB time是整个数据库用户进程消耗的总时间，是从第一项到第十项时间的总和（从sql execute elapsed time到PL/SQL compilation elapsed time），但是我们会发现这十项时间的总和比DB Time要大一些，这是因为部分时间信息有重叠的部分，比如SQL execute elapsed time就包括了很大一部分DB cpu的时间。而background elapsed time和background cpu time则是Oracle后台进程消耗的时间和cpu time。

**数据库响应时间分析：**

**    数据库系统的响应时间由四个要素决定：CPU，IO，内存和网络**，**其中CPU和IO是最重要的因素。**与之相比，内存与网络则简单很多，因为通常情况下，对于一个调优的系统来说，内存访问的延迟时间非常小（100 ns以下，1 ms=1000000 ns）相比较CPU和IO几乎可以忽略。而网络延迟则通常是一个常数，比如在一个数据中心的情况下，网络的延迟一般在3ms以下，如果存在多数据中心的情况，网络延迟可能会超过20ms，所以对于一个分布式系统来说，网络延迟是必须要考虑的问题。

在这里，我们不考虑分布式系统，并且忽略内存的访问延迟，重点分析CPU和IO，我们看以下数据库的AWR片段：

<table> 
 <tbody style="margin:0px;padding:0px;"> 
 <tr style="margin:0px;padding:0px;"> 
 <th style="margin:0px;border-left-style:dotted;border-left-color:rgb(255,255,255);border-right-style:dotted;border-right-color:rgb(255,255,255);border-bottom-color:rgb(255,255,255);vertical-align:middle;background-color:rgb(225,231,233);">Wait Class</th> 
 <th style="margin:0px;border-left-style:dotted;border-left-color:rgb(255,255,255);border-right-style:dotted;border-right-color:rgb(255,255,255);border-bottom-color:rgb(255,255,255);vertical-align:middle;background-color:rgb(225,231,233);">Waits</th> 
 <th style="margin:0px;border-left-style:dotted;border-left-color:rgb(255,255,255);border-right-style:dotted;border-right-color:rgb(255,255,255);border-bottom-color:rgb(255,255,255);vertical-align:middle;background-color:rgb(225,231,233);">%Time -outs</th> 
 <th style="margin:0px;border-left-style:dotted;border-left-color:rgb(255,255,255);border-right-style:dotted;border-right-color:rgb(255,255,255);border-bottom-color:rgb(255,255,255);vertical-align:middle;background-color:rgb(225,231,233);">Total Wait Time (s)</th> 
 <th style="margin:0px;border-left-style:dotted;border-left-color:rgb(255,255,255);border-right-style:dotted;border-right-color:rgb(255,255,255);border-bottom-color:rgb(255,255,255);vertical-align:middle;background-color:rgb(225,231,233);">Avg wait (ms)</th> 
 <th style="margin:0px;border-left-style:dotted;border-left-color:rgb(255,255,255);border-right-style:dotted;border-right-color:rgb(255,255,255);border-bottom-color:rgb(255,255,255);vertical-align:middle;background-color:rgb(225,231,233);">%DB time</th> 
 </tr> 
 <tr style="margin:0px;padding:0px;"> 
 <td style="margin:0px;border-left-style:dotted;border-left-color:rgb(255,255,255);border-right-style:dotted;border-right-color:rgb(255,255,255);border-bottom-color:rgb(255,255,255);vertical-align:middle;background-color:rgb(241,245,246);">DB CPU</td> 
 <td align="right" style="margin:0px;border-left-style:dotted;border-left-color:rgb(255,255,255);border-right-style:dotted;border-right-color:rgb(255,255,255);border-bottom-color:rgb(255,255,255);vertical-align:middle;background-color:rgb(241,245,246);"> </td> 
 <td align="right" style="margin:0px;border-left-style:dotted;border-left-color:rgb(255,255,255);border-right-style:dotted;border-right-color:rgb(255,255,255);border-bottom-color:rgb(255,255,255);vertical-align:middle;background-color:rgb(241,245,246);"> </td> 
 <td align="right" style="margin:0px;border-left-style:dotted;border-left-color:rgb(255,255,255);border-right-style:dotted;border-right-color:rgb(255,255,255);border-bottom-color:rgb(255,255,255);vertical-align:middle;background-color:rgb(241,245,246);">3,351</td> 
 <td align="right" style="margin:0px;border-left-style:dotted;border-left-color:rgb(255,255,255);border-right-style:dotted;border-right-color:rgb(255,255,255);border-bottom-color:rgb(255,255,255);vertical-align:middle;background-color:rgb(241,245,246);"> </td> 
 <td align="right" style="margin:0px;border-left-style:dotted;border-left-color:rgb(255,255,255);border-right-style:dotted;border-right-color:rgb(255,255,255);border-bottom-color:rgb(255,255,255);vertical-align:middle;background-color:rgb(241,245,246);">87.21</td> 
 </tr> 
 <tr style="margin:0px;padding:0px;"> 
 <td style="margin:0px;border-left-style:dotted;border-left-color:rgb(255,255,255);border-right-style:dotted;border-right-color:rgb(255,255,255);border-bottom-color:rgb(255,255,255);vertical-align:middle;background-color:rgb(241,245,246);">User I/O</td> 
 <td align="right" style="margin:0px;border-left-style:dotted;border-left-color:rgb(255,255,255);border-right-style:dotted;border-right-color:rgb(255,255,255);border-bottom-color:rgb(255,255,255);vertical-align:middle;background-color:rgb(241,245,246);">257,450</td> 
 <td align="right" style="margin:0px;border-left-style:dotted;border-left-color:rgb(255,255,255);border-right-style:dotted;border-right-color:rgb(255,255,255);border-bottom-color:rgb(255,255,255);vertical-align:middle;background-color:rgb(241,245,246);">0</td> 
 <td align="right" style="margin:0px;border-left-style:dotted;border-left-color:rgb(255,255,255);border-right-style:dotted;border-right-color:rgb(255,255,255);border-bottom-color:rgb(255,255,255);vertical-align:middle;background-color:rgb(241,245,246);">350</td> 
 <td align="right" style="margin:0px;border-left-style:dotted;border-left-color:rgb(255,255,255);border-right-style:dotted;border-right-color:rgb(255,255,255);border-bottom-color:rgb(255,255,255);vertical-align:middle;background-color:rgb(241,245,246);">1</td> 
 <td align="right" style="margin:0px;border-left-style:dotted;border-left-color:rgb(255,255,255);border-right-style:dotted;border-right-color:rgb(255,255,255);border-bottom-color:rgb(255,255,255);vertical-align:middle;background-color:rgb(241,245,246);">9.12</td> 
 </tr> 
 <tr style="margin:0px;padding:0px;"> 
 <td style="margin:0px;border-left-style:dotted;border-left-color:rgb(255,255,255);border-right-style:dotted;border-right-color:rgb(255,255,255);border-bottom-color:rgb(255,255,255);vertical-align:middle;background-color:rgb(241,245,246);">Commit</td> 
 <td align="right" style="margin:0px;border-left-style:dotted;border-left-color:rgb(255,255,255);border-right-style:dotted;border-right-color:rgb(255,255,255);border-bottom-color:rgb(255,255,255);vertical-align:middle;background-color:rgb(241,245,246);">127,672</td> 
 <td align="right" style="margin:0px;border-left-style:dotted;border-left-color:rgb(255,255,255);border-right-style:dotted;border-right-color:rgb(255,255,255);border-bottom-color:rgb(255,255,255);vertical-align:middle;background-color:rgb(241,245,246);">0</td> 
 <td align="right" style="margin:0px;border-left-style:dotted;border-left-color:rgb(255,255,255);border-right-style:dotted;border-right-color:rgb(255,255,255);border-bottom-color:rgb(255,255,255);vertical-align:middle;background-color:rgb(241,245,246);">90</td> 
 <td align="right" style="margin:0px;border-left-style:dotted;border-left-color:rgb(255,255,255);border-right-style:dotted;border-right-color:rgb(255,255,255);border-bottom-color:rgb(255,255,255);vertical-align:middle;background-color:rgb(241,245,246);">1</td> 
 <td align="right" style="margin:0px;border-left-style:dotted;border-left-color:rgb(255,255,255);border-right-style:dotted;border-right-color:rgb(255,255,255);border-bottom-color:rgb(255,255,255);vertical-align:middle;background-color:rgb(241,245,246);">2.35</td> 
 </tr> 
 <tr style="margin:0px;padding:0px;"> 
 <td style="margin:0px;border-left-style:dotted;border-left-color:rgb(255,255,255);border-right-style:dotted;border-right-color:rgb(255,255,255);border-bottom-color:rgb(255,255,255);vertical-align:middle;background-color:rgb(241,245,246);">Cluster</td> 
 <td align="right" style="margin:0px;border-left-style:dotted;border-left-color:rgb(255,255,255);border-right-style:dotted;border-right-color:rgb(255,255,255);border-bottom-color:rgb(255,255,255);vertical-align:middle;background-color:rgb(241,245,246);">53,770</td> 
 <td align="right" style="margin:0px;border-left-style:dotted;border-left-color:rgb(255,255,255);border-right-style:dotted;border-right-color:rgb(255,255,255);border-bottom-color:rgb(255,255,255);vertical-align:middle;background-color:rgb(241,245,246);">0</td> 
 <td align="right" style="margin:0px;border-left-style:dotted;border-left-color:rgb(255,255,255);border-right-style:dotted;border-right-color:rgb(255,255,255);border-bottom-color:rgb(255,255,255);vertical-align:middle;background-color:rgb(241,245,246);">10</td> 
 <td align="right" style="margin:0px;border-left-style:dotted;border-left-color:rgb(255,255,255);border-right-style:dotted;border-right-color:rgb(255,255,255);border-bottom-color:rgb(255,255,255);vertical-align:middle;background-color:rgb(241,245,246);">0</td> 
 <td align="right" style="margin:0px;border-left-style:dotted;border-left-color:rgb(255,255,255);border-right-style:dotted;border-right-color:rgb(255,255,255);border-bottom-color:rgb(255,255,255);vertical-align:middle;background-color:rgb(241,245,246);">0.27</td> 
 </tr> 
 <tr style="margin:0px;padding:0px;"> 
 <td style="margin:0px;border-left-style:dotted;border-left-color:rgb(255,255,255);border-right-style:dotted;border-right-color:rgb(255,255,255);border-bottom-color:rgb(255,255,255);vertical-align:middle;background-color:rgb(241,245,246);">Concurrency</td> 
 <td align="right" style="margin:0px;border-left-style:dotted;border-left-color:rgb(255,255,255);border-right-style:dotted;border-right-color:rgb(255,255,255);border-bottom-color:rgb(255,255,255);vertical-align:middle;background-color:rgb(241,245,246);">25,652</td> 
 <td align="right" style="margin:0px;border-left-style:dotted;border-left-color:rgb(255,255,255);border-right-style:dotted;border-right-color:rgb(255,255,255);border-bottom-color:rgb(255,255,255);vertical-align:middle;background-color:rgb(241,245,246);">7</td> 
 <td align="right" style="margin:0px;border-left-style:dotted;border-left-color:rgb(255,255,255);border-right-style:dotted;border-right-color:rgb(255,255,255);border-bottom-color:rgb(255,255,255);vertical-align:middle;background-color:rgb(241,245,246);">9</td> 
 <td align="right" style="margin:0px;border-left-style:dotted;border-left-color:rgb(255,255,255);border-right-style:dotted;border-right-color:rgb(255,255,255);border-bottom-color:rgb(255,255,255);vertical-align:middle;background-color:rgb(241,245,246);">0</td> 
 <td align="right" style="margin:0px;border-left-style:dotted;border-left-color:rgb(255,255,255);border-right-style:dotted;border-right-color:rgb(255,255,255);border-bottom-color:rgb(255,255,255);vertical-align:middle;background-color:rgb(241,245,246);">0.24</td> 
 </tr> 
 <tr style="margin:0px;padding:0px;"> 
 <td style="margin:0px;border-left-style:dotted;border-left-color:rgb(255,255,255);border-right-style:dotted;border-right-color:rgb(255,255,255);border-bottom-color:rgb(255,255,255);vertical-align:middle;background-color:rgb(241,245,246);">System I/O</td> 
 <td align="right" style="margin:0px;border-left-style:dotted;border-left-color:rgb(255,255,255);border-right-style:dotted;border-right-color:rgb(255,255,255);border-bottom-color:rgb(255,255,255);vertical-align:middle;background-color:rgb(241,245,246);">3,623</td> 
 <td align="right" style="margin:0px;border-left-style:dotted;border-left-color:rgb(255,255,255);border-right-style:dotted;border-right-color:rgb(255,255,255);border-bottom-color:rgb(255,255,255);vertical-align:middle;background-color:rgb(241,245,246);">0</td> 
 <td align="right" style="margin:0px;border-left-style:dotted;border-left-color:rgb(255,255,255);border-right-style:dotted;border-right-color:rgb(255,255,255);border-bottom-color:rgb(255,255,255);vertical-align:middle;background-color:rgb(241,245,246);">6</td> 
 <td align="right" style="margin:0px;border-left-style:dotted;border-left-color:rgb(255,255,255);border-right-style:dotted;border-right-color:rgb(255,255,255);border-bottom-color:rgb(255,255,255);vertical-align:middle;background-color:rgb(241,245,246);">2</td> 
 <td align="right" style="margin:0px;border-left-style:dotted;border-left-color:rgb(255,255,255);border-right-style:dotted;border-right-color:rgb(255,255,255);border-bottom-color:rgb(255,255,255);vertical-align:middle;background-color:rgb(241,245,246);">0.15</td> 
 </tr> 
 <tr style="margin:0px;padding:0px;"> 
 <td style="margin:0px;border-left-style:dotted;border-left-color:rgb(255,255,255);border-right-style:dotted;border-right-color:rgb(255,255,255);border-bottom-color:rgb(255,255,255);vertical-align:middle;background-color:rgb(241,245,246);">Network</td> 
 <td align="right" style="margin:0px;border-left-style:dotted;border-left-color:rgb(255,255,255);border-right-style:dotted;border-right-color:rgb(255,255,255);border-bottom-color:rgb(255,255,255);vertical-align:middle;background-color:rgb(241,245,246);">2,069,001</td> 
 <td align="right" style="margin:0px;border-left-style:dotted;border-left-color:rgb(255,255,255);border-right-style:dotted;border-right-color:rgb(255,255,255);border-bottom-color:rgb(255,255,255);vertical-align:middle;background-color:rgb(241,245,246);">0</td> 
 <td align="right" style="margin:0px;border-left-style:dotted;border-left-color:rgb(255,255,255);border-right-style:dotted;border-right-color:rgb(255,255,255);border-bottom-color:rgb(255,255,255);vertical-align:middle;background-color:rgb(241,245,246);">5</td> 
 <td align="right" style="margin:0px;border-left-style:dotted;border-left-color:rgb(255,255,255);border-right-style:dotted;border-right-color:rgb(255,255,255);border-bottom-color:rgb(255,255,255);vertical-align:middle;background-color:rgb(241,245,246);">0</td> 
 <td align="right" style="margin:0px;border-left-style:dotted;border-left-color:rgb(255,255,255);border-right-style:dotted;border-right-color:rgb(255,255,255);border-bottom-color:rgb(255,255,255);vertical-align:middle;background-color:rgb(241,245,246);">0.14</td> 
 </tr> 
 <tr style="margin:0px;padding:0px;"> 
 <td style="margin:0px;border-left-style:dotted;border-left-color:rgb(255,255,255);border-right-style:dotted;border-right-color:rgb(255,255,255);border-bottom-color:rgb(255,255,255);vertical-align:middle;background-color:rgb(241,245,246);">Application</td> 
 <td align="right" style="margin:0px;border-left-style:dotted;border-left-color:rgb(255,255,255);border-right-style:dotted;border-right-color:rgb(255,255,255);border-bottom-color:rgb(255,255,255);vertical-align:middle;background-color:rgb(241,245,246);">679</td> 
 <td align="right" style="margin:0px;border-left-style:dotted;border-left-color:rgb(255,255,255);border-right-style:dotted;border-right-color:rgb(255,255,255);border-bottom-color:rgb(255,255,255);vertical-align:middle;background-color:rgb(241,245,246);">0</td> 
 <td align="right" style="margin:0px;border-left-style:dotted;border-left-color:rgb(255,255,255);border-right-style:dotted;border-right-color:rgb(255,255,255);border-bottom-color:rgb(255,255,255);vertical-align:middle;background-color:rgb(241,245,246);">5</td> 
 <td align="right" style="margin:0px;border-left-style:dotted;border-left-color:rgb(255,255,255);border-right-style:dotted;border-right-color:rgb(255,255,255);border-bottom-color:rgb(255,255,255);vertical-align:middle;background-color:rgb(241,245,246);">7</td> 
 <td align="right" style="margin:0px;border-left-style:dotted;border-left-color:rgb(255,255,255);border-right-style:dotted;border-right-color:rgb(255,255,255);border-bottom-color:rgb(255,255,255);vertical-align:middle;background-color:rgb(241,245,246);">0.13</td> 
 </tr> 
 <tr style="margin:0px;padding:0px;"> 
 <td style="margin:0px;border-left-style:dotted;border-left-color:rgb(255,255,255);border-right-style:dotted;border-right-color:rgb(255,255,255);border-bottom-color:rgb(255,255,255);vertical-align:middle;background-color:rgb(241,245,246);">Other</td> 
 <td align="right" style="margin:0px;border-left-style:dotted;border-left-color:rgb(255,255,255);border-right-style:dotted;border-right-color:rgb(255,255,255);border-bottom-color:rgb(255,255,255);vertical-align:middle;background-color:rgb(241,245,246);">20,828</td> 
 <td align="right" style="margin:0px;border-left-style:dotted;border-left-color:rgb(255,255,255);border-right-style:dotted;border-right-color:rgb(255,255,255);border-bottom-color:rgb(255,255,255);vertical-align:middle;background-color:rgb(241,245,246);">78</td> 
 <td align="right" style="margin:0px;border-left-style:dotted;border-left-color:rgb(255,255,255);border-right-style:dotted;border-right-color:rgb(255,255,255);border-bottom-color:rgb(255,255,255);vertical-align:middle;background-color:rgb(241,245,246);">4</td> 
 <td align="right" style="margin:0px;border-left-style:dotted;border-left-color:rgb(255,255,255);border-right-style:dotted;border-right-color:rgb(255,255,255);border-bottom-color:rgb(255,255,255);vertical-align:middle;background-color:rgb(241,245,246);">0</td> 
 <td align="right" style="margin:0px;border-left-style:dotted;border-left-color:rgb(255,255,255);border-right-style:dotted;border-right-color:rgb(255,255,255);border-bottom-color:rgb(255,255,255);vertical-align:middle;background-color:rgb(241,245,246);">0.10</td> 
 </tr> 
 <tr style="margin:0px;padding:0px;"> 
 <td style="margin:0px;border-left-style:dotted;border-left-color:rgb(255,255,255);border-right-style:dotted;border-right-color:rgb(255,255,255);border-bottom-color:rgb(255,255,255);vertical-align:middle;background-color:rgb(241,245,246);">Configuration</td> 
 <td align="right" style="margin:0px;border-left-style:dotted;border-left-color:rgb(255,255,255);border-right-style:dotted;border-right-color:rgb(255,255,255);border-bottom-color:rgb(255,255,255);vertical-align:middle;background-color:rgb(241,245,246);">2,353</td> 
 <td align="right" style="margin:0px;border-left-style:dotted;border-left-color:rgb(255,255,255);border-right-style:dotted;border-right-color:rgb(255,255,255);border-bottom-color:rgb(255,255,255);vertical-align:middle;background-color:rgb(241,245,246);">0</td> 
 <td align="right" style="margin:0px;border-left-style:dotted;border-left-color:rgb(255,255,255);border-right-style:dotted;border-right-color:rgb(255,255,255);border-bottom-color:rgb(255,255,255);vertical-align:middle;background-color:rgb(241,245,246);">2</td> 
 <td align="right" style="margin:0px;border-left-style:dotted;border-left-color:rgb(255,255,255);border-right-style:dotted;border-right-color:rgb(255,255,255);border-bottom-color:rgb(255,255,255);vertical-align:middle;background-color:rgb(241,245,246);">1</td> 
 <td align="right" style="margin:0px;border-left-style:dotted;border-left-color:rgb(255,255,255);border-right-style:dotted;border-right-color:rgb(255,255,255);border-bottom-color:rgb(255,255,255);vertical-align:middle;background-color:rgb(241,245,246);">0.06</td> 
 </tr> 
 </tbody> 
</table>

我们看到这个系统中DB CPU占整个DB time的87.21%，User I/O占整个DB time的9.12%，commit相关的IO等待占2.35%（主要是log file sync），CPU和IO占用了整个DB time的96.68%。由于DB CPU所占的比例很高，所以这个数据库系统是CPU intensive类型，这里的DB CPU主要是执行SQL的服务时间。

我们再看另外的一个数据库的AWR片段：

<table> 
 <tbody style="margin:0px;padding:0px;"> 
 <tr style="margin:0px;padding:0px;"> 
 <th style="margin:0px;border-left-style:dotted;border-left-color:rgb(255,255,255);border-right-style:dotted;border-right-color:rgb(255,255,255);border-bottom-color:rgb(255,255,255);vertical-align:middle;background-color:rgb(225,231,233);">Wait Class</th> 
 <th style="margin:0px;border-left-style:dotted;border-left-color:rgb(255,255,255);border-right-style:dotted;border-right-color:rgb(255,255,255);border-bottom-color:rgb(255,255,255);vertical-align:middle;background-color:rgb(225,231,233);">Waits</th> 
 <th style="margin:0px;border-left-style:dotted;border-left-color:rgb(255,255,255);border-right-style:dotted;border-right-color:rgb(255,255,255);border-bottom-color:rgb(255,255,255);vertical-align:middle;background-color:rgb(225,231,233);">%Time -outs</th> 
 <th style="margin:0px;border-left-style:dotted;border-left-color:rgb(255,255,255);border-right-style:dotted;border-right-color:rgb(255,255,255);border-bottom-color:rgb(255,255,255);vertical-align:middle;background-color:rgb(225,231,233);">Total Wait Time (s)</th> 
 <th style="margin:0px;border-left-style:dotted;border-left-color:rgb(255,255,255);border-right-style:dotted;border-right-color:rgb(255,255,255);border-bottom-color:rgb(255,255,255);vertical-align:middle;background-color:rgb(225,231,233);">Avg wait (ms)</th> 
 <th style="margin:0px;border-left-style:dotted;border-left-color:rgb(255,255,255);border-right-style:dotted;border-right-color:rgb(255,255,255);border-bottom-color:rgb(255,255,255);vertical-align:middle;background-color:rgb(225,231,233);">%DB time</th> 
 </tr> 
 <tr style="margin:0px;padding:0px;"> 
 <td style="margin:0px;border-left-style:dotted;border-left-color:rgb(255,255,255);border-right-style:dotted;border-right-color:rgb(255,255,255);border-bottom-color:rgb(255,255,255);vertical-align:middle;background-color:rgb(241,245,246);">Commit</td> 
 <td align="right" style="margin:0px;border-left-style:dotted;border-left-color:rgb(255,255,255);border-right-style:dotted;border-right-color:rgb(255,255,255);border-bottom-color:rgb(255,255,255);vertical-align:middle;background-color:rgb(241,245,246);">817,470</td> 
 <td align="right" style="margin:0px;border-left-style:dotted;border-left-color:rgb(255,255,255);border-right-style:dotted;border-right-color:rgb(255,255,255);border-bottom-color:rgb(255,255,255);vertical-align:middle;background-color:rgb(241,245,246);">0</td> 
 <td align="right" style="margin:0px;border-left-style:dotted;border-left-color:rgb(255,255,255);border-right-style:dotted;border-right-color:rgb(255,255,255);border-bottom-color:rgb(255,255,255);vertical-align:middle;background-color:rgb(241,245,246);">5,232</td> 
 <td align="right" style="margin:0px;border-left-style:dotted;border-left-color:rgb(255,255,255);border-right-style:dotted;border-right-color:rgb(255,255,255);border-bottom-color:rgb(255,255,255);vertical-align:middle;background-color:rgb(241,245,246);">6</td> 
 <td align="right" style="margin:0px;border-left-style:dotted;border-left-color:rgb(255,255,255);border-right-style:dotted;border-right-color:rgb(255,255,255);border-bottom-color:rgb(255,255,255);vertical-align:middle;background-color:rgb(241,245,246);">67.49</td> 
 </tr> 
 <tr style="margin:0px;padding:0px;"> 
 <td style="margin:0px;border-left-style:dotted;border-left-color:rgb(255,255,255);border-right-style:dotted;border-right-color:rgb(255,255,255);border-bottom-color:rgb(255,255,255);vertical-align:middle;background-color:rgb(241,245,246);">User I/O</td> 
 <td align="right" style="margin:0px;border-left-style:dotted;border-left-color:rgb(255,255,255);border-right-style:dotted;border-right-color:rgb(255,255,255);border-bottom-color:rgb(255,255,255);vertical-align:middle;background-color:rgb(241,245,246);">238,850</td> 
 <td align="right" style="margin:0px;border-left-style:dotted;border-left-color:rgb(255,255,255);border-right-style:dotted;border-right-color:rgb(255,255,255);border-bottom-color:rgb(255,255,255);vertical-align:middle;background-color:rgb(241,245,246);">0</td> 
 <td align="right" style="margin:0px;border-left-style:dotted;border-left-color:rgb(255,255,255);border-right-style:dotted;border-right-color:rgb(255,255,255);border-bottom-color:rgb(255,255,255);vertical-align:middle;background-color:rgb(241,245,246);">1,083</td> 
 <td align="right" style="margin:0px;border-left-style:dotted;border-left-color:rgb(255,255,255);border-right-style:dotted;border-right-color:rgb(255,255,255);border-bottom-color:rgb(255,255,255);vertical-align:middle;background-color:rgb(241,245,246);">5</td> 
 <td align="right" style="margin:0px;border-left-style:dotted;border-left-color:rgb(255,255,255);border-right-style:dotted;border-right-color:rgb(255,255,255);border-bottom-color:rgb(255,255,255);vertical-align:middle;background-color:rgb(241,245,246);">13.97</td> 
 </tr> 
 <tr style="margin:0px;padding:0px;"> 
 <td style="margin:0px;border-left-style:dotted;border-left-color:rgb(255,255,255);border-right-style:dotted;border-right-color:rgb(255,255,255);border-bottom-color:rgb(255,255,255);vertical-align:middle;background-color:rgb(241,245,246);">DB CPU</td> 
 <td align="right" style="margin:0px;border-left-style:dotted;border-left-color:rgb(255,255,255);border-right-style:dotted;border-right-color:rgb(255,255,255);border-bottom-color:rgb(255,255,255);vertical-align:middle;background-color:rgb(241,245,246);"> </td> 
 <td align="right" style="margin:0px;border-left-style:dotted;border-left-color:rgb(255,255,255);border-right-style:dotted;border-right-color:rgb(255,255,255);border-bottom-color:rgb(255,255,255);vertical-align:middle;background-color:rgb(241,245,246);"> </td> 
 <td align="right" style="margin:0px;border-left-style:dotted;border-left-color:rgb(255,255,255);border-right-style:dotted;border-right-color:rgb(255,255,255);border-bottom-color:rgb(255,255,255);vertical-align:middle;background-color:rgb(241,245,246);">1,071</td> 
 <td align="right" style="margin:0px;border-left-style:dotted;border-left-color:rgb(255,255,255);border-right-style:dotted;border-right-color:rgb(255,255,255);border-bottom-color:rgb(255,255,255);vertical-align:middle;background-color:rgb(241,245,246);"> </td> 
 <td align="right" style="margin:0px;border-left-style:dotted;border-left-color:rgb(255,255,255);border-right-style:dotted;border-right-color:rgb(255,255,255);border-bottom-color:rgb(255,255,255);vertical-align:middle;background-color:rgb(241,245,246);">13.82</td> 
 </tr> 
 <tr style="margin:0px;padding:0px;"> 
 <td style="margin:0px;border-left-style:dotted;border-left-color:rgb(255,255,255);border-right-style:dotted;border-right-color:rgb(255,255,255);border-bottom-color:rgb(255,255,255);vertical-align:middle;background-color:rgb(241,245,246);">Configuration</td> 
 <td align="right" style="margin:0px;border-left-style:dotted;border-left-color:rgb(255,255,255);border-right-style:dotted;border-right-color:rgb(255,255,255);border-bottom-color:rgb(255,255,255);vertical-align:middle;background-color:rgb(241,245,246);">4,150</td> 
 <td align="right" style="margin:0px;border-left-style:dotted;border-left-color:rgb(255,255,255);border-right-style:dotted;border-right-color:rgb(255,255,255);border-bottom-color:rgb(255,255,255);vertical-align:middle;background-color:rgb(241,245,246);">1</td> 
 <td align="right" style="margin:0px;border-left-style:dotted;border-left-color:rgb(255,255,255);border-right-style:dotted;border-right-color:rgb(255,255,255);border-bottom-color:rgb(255,255,255);vertical-align:middle;background-color:rgb(241,245,246);">403</td> 
 <td align="right" style="margin:0px;border-left-style:dotted;border-left-color:rgb(255,255,255);border-right-style:dotted;border-right-color:rgb(255,255,255);border-bottom-color:rgb(255,255,255);vertical-align:middle;background-color:rgb(241,245,246);">97</td> 
 <td align="right" style="margin:0px;border-left-style:dotted;border-left-color:rgb(255,255,255);border-right-style:dotted;border-right-color:rgb(255,255,255);border-bottom-color:rgb(255,255,255);vertical-align:middle;background-color:rgb(241,245,246);">5.20</td> 
 </tr> 
 <tr style="margin:0px;padding:0px;"> 
 <td style="margin:0px;border-left-style:dotted;border-left-color:rgb(255,255,255);border-right-style:dotted;border-right-color:rgb(255,255,255);border-bottom-color:rgb(255,255,255);vertical-align:middle;background-color:rgb(241,245,246);">Concurrency</td> 
 <td align="right" style="margin:0px;border-left-style:dotted;border-left-color:rgb(255,255,255);border-right-style:dotted;border-right-color:rgb(255,255,255);border-bottom-color:rgb(255,255,255);vertical-align:middle;background-color:rgb(241,245,246);">42,626</td> 
 <td align="right" style="margin:0px;border-left-style:dotted;border-left-color:rgb(255,255,255);border-right-style:dotted;border-right-color:rgb(255,255,255);border-bottom-color:rgb(255,255,255);vertical-align:middle;background-color:rgb(241,245,246);">27</td> 
 <td align="right" style="margin:0px;border-left-style:dotted;border-left-color:rgb(255,255,255);border-right-style:dotted;border-right-color:rgb(255,255,255);border-bottom-color:rgb(255,255,255);vertical-align:middle;background-color:rgb(241,245,246);">31</td> 
 <td align="right" style="margin:0px;border-left-style:dotted;border-left-color:rgb(255,255,255);border-right-style:dotted;border-right-color:rgb(255,255,255);border-bottom-color:rgb(255,255,255);vertical-align:middle;background-color:rgb(241,245,246);">1</td> 
 <td align="right" style="margin:0px;border-left-style:dotted;border-left-color:rgb(255,255,255);border-right-style:dotted;border-right-color:rgb(255,255,255);border-bottom-color:rgb(255,255,255);vertical-align:middle;background-color:rgb(241,245,246);">0.40</td> 
 </tr> 
 <tr style="margin:0px;padding:0px;"> 
 <td style="margin:0px;border-left-style:dotted;border-left-color:rgb(255,255,255);border-right-style:dotted;border-right-color:rgb(255,255,255);border-bottom-color:rgb(255,255,255);vertical-align:middle;background-color:rgb(241,245,246);">System I/O</td> 
 <td align="right" style="margin:0px;border-left-style:dotted;border-left-color:rgb(255,255,255);border-right-style:dotted;border-right-color:rgb(255,255,255);border-bottom-color:rgb(255,255,255);vertical-align:middle;background-color:rgb(241,245,246);">23,742</td> 
 <td align="right" style="margin:0px;border-left-style:dotted;border-left-color:rgb(255,255,255);border-right-style:dotted;border-right-color:rgb(255,255,255);border-bottom-color:rgb(255,255,255);vertical-align:middle;background-color:rgb(241,245,246);">0</td> 
 <td align="right" style="margin:0px;border-left-style:dotted;border-left-color:rgb(255,255,255);border-right-style:dotted;border-right-color:rgb(255,255,255);border-bottom-color:rgb(255,255,255);vertical-align:middle;background-color:rgb(241,245,246);">6</td> 
 <td align="right" style="margin:0px;border-left-style:dotted;border-left-color:rgb(255,255,255);border-right-style:dotted;border-right-color:rgb(255,255,255);border-bottom-color:rgb(255,255,255);vertical-align:middle;background-color:rgb(241,245,246);">0</td> 
 <td align="right" style="margin:0px;border-left-style:dotted;border-left-color:rgb(255,255,255);border-right-style:dotted;border-right-color:rgb(255,255,255);border-bottom-color:rgb(255,255,255);vertical-align:middle;background-color:rgb(241,245,246);">0.07</td> 
 </tr> 
 <tr style="margin:0px;padding:0px;"> 
 <td style="margin:0px;border-left-style:dotted;border-left-color:rgb(255,255,255);border-right-style:dotted;border-right-color:rgb(255,255,255);border-bottom-color:rgb(255,255,255);vertical-align:middle;background-color:rgb(241,245,246);">Network</td> 
 <td align="right" style="margin:0px;border-left-style:dotted;border-left-color:rgb(255,255,255);border-right-style:dotted;border-right-color:rgb(255,255,255);border-bottom-color:rgb(255,255,255);vertical-align:middle;background-color:rgb(241,245,246);">1,838,062</td> 
 <td align="right" style="margin:0px;border-left-style:dotted;border-left-color:rgb(255,255,255);border-right-style:dotted;border-right-color:rgb(255,255,255);border-bottom-color:rgb(255,255,255);vertical-align:middle;background-color:rgb(241,245,246);">0</td> 
 <td align="right" style="margin:0px;border-left-style:dotted;border-left-color:rgb(255,255,255);border-right-style:dotted;border-right-color:rgb(255,255,255);border-bottom-color:rgb(255,255,255);vertical-align:middle;background-color:rgb(241,245,246);">2</td> 
 <td align="right" style="margin:0px;border-left-style:dotted;border-left-color:rgb(255,255,255);border-right-style:dotted;border-right-color:rgb(255,255,255);border-bottom-color:rgb(255,255,255);vertical-align:middle;background-color:rgb(241,245,246);">0</td> 
 <td align="right" style="margin:0px;border-left-style:dotted;border-left-color:rgb(255,255,255);border-right-style:dotted;border-right-color:rgb(255,255,255);border-bottom-color:rgb(255,255,255);vertical-align:middle;background-color:rgb(241,245,246);">0.03</td> 
 </tr> 
 <tr style="margin:0px;padding:0px;"> 
 <td style="margin:0px;border-left-style:dotted;border-left-color:rgb(255,255,255);border-right-style:dotted;border-right-color:rgb(255,255,255);border-bottom-color:rgb(255,255,255);vertical-align:middle;background-color:rgb(241,245,246);">Application</td> 
 <td align="right" style="margin:0px;border-left-style:dotted;border-left-color:rgb(255,255,255);border-right-style:dotted;border-right-color:rgb(255,255,255);border-bottom-color:rgb(255,255,255);vertical-align:middle;background-color:rgb(241,245,246);">125</td> 
 <td align="right" style="margin:0px;border-left-style:dotted;border-left-color:rgb(255,255,255);border-right-style:dotted;border-right-color:rgb(255,255,255);border-bottom-color:rgb(255,255,255);vertical-align:middle;background-color:rgb(241,245,246);">0</td> 
 <td align="right" style="margin:0px;border-left-style:dotted;border-left-color:rgb(255,255,255);border-right-style:dotted;border-right-color:rgb(255,255,255);border-bottom-color:rgb(255,255,255);vertical-align:middle;background-color:rgb(241,245,246);">0</td> 
 <td align="right" style="margin:0px;border-left-style:dotted;border-left-color:rgb(255,255,255);border-right-style:dotted;border-right-color:rgb(255,255,255);border-bottom-color:rgb(255,255,255);vertical-align:middle;background-color:rgb(241,245,246);">2</td> 
 <td align="right" style="margin:0px;border-left-style:dotted;border-left-color:rgb(255,255,255);border-right-style:dotted;border-right-color:rgb(255,255,255);border-bottom-color:rgb(255,255,255);vertical-align:middle;background-color:rgb(241,245,246);">0.00</td> 
 </tr> 
 <tr style="margin:0px;padding:0px;"> 
 <td style="margin:0px;border-left-style:dotted;border-left-color:rgb(255,255,255);border-right-style:dotted;border-right-color:rgb(255,255,255);border-bottom-color:rgb(255,255,255);vertical-align:middle;background-color:rgb(241,245,246);">Other</td> 
 <td align="right" style="margin:0px;border-left-style:dotted;border-left-color:rgb(255,255,255);border-right-style:dotted;border-right-color:rgb(255,255,255);border-bottom-color:rgb(255,255,255);vertical-align:middle;background-color:rgb(241,245,246);">2,026</td> 
 <td align="right" style="margin:0px;border-left-style:dotted;border-left-color:rgb(255,255,255);border-right-style:dotted;border-right-color:rgb(255,255,255);border-bottom-color:rgb(255,255,255);vertical-align:middle;background-color:rgb(241,245,246);">82</td> 
 <td align="right" style="margin:0px;border-left-style:dotted;border-left-color:rgb(255,255,255);border-right-style:dotted;border-right-color:rgb(255,255,255);border-bottom-color:rgb(255,255,255);vertical-align:middle;background-color:rgb(241,245,246);">0</td> 
 <td align="right" style="margin:0px;border-left-style:dotted;border-left-color:rgb(255,255,255);border-right-style:dotted;border-right-color:rgb(255,255,255);border-bottom-color:rgb(255,255,255);vertical-align:middle;background-color:rgb(241,245,246);">0</td> 
 <td align="right" style="margin:0px;border-left-style:dotted;border-left-color:rgb(255,255,255);border-right-style:dotted;border-right-color:rgb(255,255,255);border-bottom-color:rgb(255,255,255);vertical-align:middle;background-color:rgb(241,245,246);">0.00</td> 
 </tr> 
 </tbody> 
</table>

我们看到，Commit和User I/O占DB time的81.46%，而DB CPU只占13.82%，所以这个数据库系统是IO instensive类型的。

**Physical read**

Physical read是指Oracle在buffer cache中没有找到相应的block，需要从IO子系统读取相应的block的过程，对应的IO称为物理IO，物理读数量代表物理IO读取的block数量。因为一般IO子系统都是慢速的磁盘，所以物理IO对整体响应时间的影响非常大，如果发生大量的物理IO，整个系统的响应时间会变得很差。系统的IO子系统可能是文件系统，裸设备或者ASM，底层硬件可能是SAN存储，NAS存储或者普通SAS磁盘等等。为了提高响应时间，通常在物理磁盘与Oracle之间增加cache层，对于Oracle来说，物理IO并不一定是真正访问磁盘，很可能是访问文件系统cache，存储的cache等等。

不管IO subsystem是什么，Oracle只关心物理IO的响应时间。通过AWR报告，我们可以看到物理IO的响应时间：

**  db file sequential read（单块读，随机IO）**的平均响应时间为3ms，**db file scattered read（多块读，连续IO）**的平均响应时间是4ms，logfile file sync的平均响应时间是3ms，前两者的Wait class是User I/O，代表用户进程读操作的响应时间，logfile sync的wait class是Commit，代表lgwr进程写redo的响应时间，因为用户commit必须完成log file sync的操作，所以它也会直接影响用户进程写操作的响应时间。

关于物理IO的响应时间，我们有一个经验值。对于Sequential read和Scattered read，我们认为小于**10ms**属于正常状态，而大于10ms则认为IO subsystem的响应延迟过大。所以我们在衡量存储系统的性能时，只有响应时间在10ms以下的IO我们认为是有效的。这里有一个有趣的现象，就是sequential read和scattered read的响应时间几乎相差无几，也就是说随机IO读取8K数据和连续IO读取128K数据，响应时间差别很小，这是由磁盘的机械特性造成的，延迟时间=寻道时间+延迟时间，顺序读和离散读的寻道时间一致，只是延迟时间有很小的差异，所以两者的响应时间差异很小。

对于log file sync的响应时间，因为用户commit必须完成log file sync，所以整个系统的写操作的响应时间都取决于它的响应时间，而且从整个数据库系统的角度去看，log file sync几乎是串行的，所以这个响应时间对写操作影响非常大，我们的经验值是必须保证在**5ms**以下，如果超过5ms整个系统的写操作都会受到严重的影响。

**Logical read**

Logical read是Oracle从buffer cache中读取block的过程，对应的IO称为逻辑IO，逻辑读数量代表逻辑IO读取的block数量**。**因为Oracle必须首先将block读入buffer cache中(direct path read除外)，所以逻辑读数量包含了物理读数量。对于一个SQL来说，逻辑读数量是衡量其性能的标准，而不是物理读。虽然物理IO的响应延迟比逻辑IO大很多，但是物理读数量会随着执行次数而变化（频繁读取导致block被缓存在buffer cache中）。对于一个系统也是如此，**逻辑读应该是数据库性能评估模型的核心**，**我们需要建立逻辑读与响应时间的对应关系。**

每个逻辑读的响应时间是多少，这是一个巨大的挑战。因为每个逻辑读背后隐藏了很多动作，可能包括物理读，等待事件，CPU time等等。我对很多数据库的AWR报告做了分析，期望根据经验值建立一个简化的模型。我们假设一个数据库如果是充分调优的，除CPU time和IO以外的等待时间应该尽可能少（应小于DB time 10%）。在这个前提下，我们只关心CPU time和IO的影响，并将系统分为三类：CPU密集型，IO密集型和混合型：

**1. IO密集型**

User IO     85%

DB CPU        5%

每逻辑读响应时间0.1-0.5ms

**2. CPU密集型**

DB CPU         85%

User IO        10%

每逻辑读响应时间小于0.01ms

**3. 混合型**

User I/O     60%

DB CPU         20%

每逻辑读响应时间0.05-0.1ms

以上数据是根据很多个典型数据库的AWR报告计算出来的经验值，计算公式很简单：DB time/逻辑读=每逻辑读响应时间。因为并没有考虑硬件和OS上的差异，所以这个数值并不是特别准确，但我们还是可以发现一些规律：随着IO所占比例从10%增加到85%，响应时间也从小于0.01ms到0.5ms。

**预测系统瓶颈**

对于数据库来说，IO子系统对性能影响非常大，必须保证在一定的IO的压力下，响应延迟控制在合理的范围内（前面说的10ms和5ms）。因为每块磁盘可以承受的IOPS是基本确定的，比如15K的SAS磁盘，在响应延迟不超过10ms的前提下，可以提供150个IOPS，如果不考虑cache的影响，整个存储子系统的IOPS是比较容易计算的。我们可以在系统上线前，进行大量充分的测试，建立存储IOPS与响应延迟的模型，这样我们就可以预测出性能出现拐点的风险，提前做出扩容的判断。在AWR报告中，我们可以得到每秒的物理IO的数量和响应时间，可以方便的实现性能监控和趋势预警。

评估CPU的容量瓶颈相对简单，Oracle中CPU time的计算是每个CPU耗费时间的总和，如果有16颗(核)CPU，1个小时理论上可以提供3600×16=57600s CPU time，不超过57600s CPU time我们可以认为不会在CPU上排队，系统不会出现CPU瓶颈。但是需要注意的是，除了用户进程使用CPU以外，操作系统也需要占用CPU资源，用来管理内存和进程调度等。我们在OS上看到的CPU使用率中的sys部分就是系统占用的CPU资源，所以应该考虑至少保留10-20%的CPU资源给OS使用。

**并发访问对数据库的影响**

Oracle是一个Disk-based database，设计的出发点就是大部分数据在外部存储中，而只有小部分数据被cache在buffer中，它既不同于Memcache这类KV cache，也不同于timesten这类In-memory database。所以，就算是所有的数据都可以被cache在buffer中，在高并发访问的情况下，也可能会出现大量的latch等待，最常见的情况就是cache buffer chain。当大量并发访问同一块数据时，就很可能会出现cache buffer chain的latch争用，也就是我们常说的“热点”。

需要注意的是：Oracle中的latch等待分为spin和sleep两个部分，spin消耗cpu time，而sleep则是等待时间。所以大量的latch等待不仅仅会产生大量的等待时间，而且会消耗大量的CPU time。

Oracle是一个为并发操作而设计的数据库，大量的并发读写请求，可能会带来额外的性能消耗。比如读取一部分频繁修改的数据，Oracle为了保证一致性读的需要，会利用undo信息构造产生大量CR block，同时会产生大量的逻辑读，这样会消耗额外的CPU和响应时间。

存储也可能存在热点的问题，需要前期对存储系统充分的优化，常见的手段是利用RAID技术，将数据分散在不同的磁盘上，防止出现“热点”盘。Oracle ASM提供了Rebalance的功能，允许DBA将存储中的的数据重新分布，达到消除热点的目的。

**    总之，Oracle是一个可以提供大量并发读写访问的数据库系统，但是在很多地方，Oracle又不得采用一些串行的控制手段，比如latch，enqueue和mutex，我们要做的就是尽量降低这些串行控制对数据库整体性能的影响。**

**数据库优化原则**

**    基于响应时间的Oracle优化原则：尽量减少等待时间（Wait time），提高服务时间（Service time）**。这也是基于Oracle等待事件的分析方法的基本原则：尽量消除各种等待事件对系统的影响，从而提高系统性能和响应时间。

**    如果数据库系统除了CPU和IO以外的等待时间超过DB time的5%以上的话，可能存在某些性能问题，需要DBA采用等待事件的分析方法，对系统或应用进行优化。**

–EOF–

后记：为什么要写这么一个主题，因为最近和一位同事探讨机器自动审核SQL的问题，就想建立一个简单的模型，用来开发一个SQL审核工具，开发人员通过工具和预先建立好的模型，就可以确定这个SQL是否存在性能风险。之前我们在做SQL优化的时候，只是关注这个SQL本身是否优化，逻辑读是多少。但是，很少有人把逻辑读和响应时间之间的关系建立起来，我试图想回答这个问题。

关于容量规划和风险预测其实是一个很有意义的命题，但是我们很多时候都局限在一些具体的技术细节中，而忽略了对整个系统容量的把握，事实上，这也是非常难的一件事。也许到目前为止，我根本没有达到建立“模型”的程度，但是我试图将这些方方面面的因素联系起来，提供一些有用的经验值给大家，我觉得这个挺有意义。

在这篇文章中，我提到了几个有意义的经验值，这是我根据很多数据库AWR中的信息计算出来的，虽然不保证完全准确，但是我觉得基本是靠谱的。建议每个DBA都应该从AWR中找到这些信息，并判断自己的数据库属于哪种类型，瓶颈在哪里，是否存在性能风险。当面对诸如“硬件是否能够满足性能需求”，“系统明年是否需要扩容”，“应用是否会对系统产生影响”此类问题时，我们可以用这些经验值给出一个判断。

** 转自：Hello DBA **[**http://www.hellodb.net/2010/06/db-performance-analysis.html**][http_www.hellodb.net_2010_06_db-performance-analysis.html]

[Oracle_Time_Model]: /images/20220805/ee049111d4dc4ba88cccf6608d5496e7.png
[http_www.hellodb.net_2010_06_db-performance-analysis.html]: http://www.hellodb.net/2010/06/db-performance-analysis.html