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之前看过很多数据库报告，直到最近出现过两次严重的性能问题，非常有代表性，所以记录下来。
一次是报Oracle进程把数据库服务器的CPU弄到100%
SQL ordered by Gets 是在内存中取数据，单位是次，是消耗CPU的主要源头，在调试SQL的时候，大部分时候都是通过它来衡量性能。下面是实际的AWR报告，相当骇人啊：
| Buffer Gets | Executions | Gets per Exec | %Total | CPU Time (s) | Elapsed Time (s) | SQL Id | SQL Module | SQL Text |
|---|---|---|---|---|---|---|---|---|
| 1,606,380,390 | 84 | 19,123,576.07 | -0.84 | 37923.62 | 207407.54 | 78tpfukr4m00p | JDBC Thin Client | select sum(temp.MidUser) total... |
| 1,479,957,445 | 0 | -0.77 | 26647.48 | 43778.62 | 2mxgaus0t6pxz | JDBC Thin Client | SELECT 设备ID SBID, 设备ID SBBM, 设... | |
| 1,280,365,092 | 73 | 17,539,247.84 | -0.67 | 30263.02 | 159789.71 | 2qrj96dwj2xx1 | JDBC Thin Client | select sum(temp.MidUser) total... |
| 1,163,229,240 | 518 | 2,245,616.29 | -0.61 | 11775.72 | 30158.95 | cq0adyp396538 | JDBC Thin Client | SELECT COUNT(*) FROM DM_FL_OBJ... |
| 465,618,308 | 261 | 1,783,978.19 | -0.24 | 11004.49 | 27015.23 | acqqmk9b7vc4a | JDBC Thin Client | SELECT COUNT(*) FROM DM_FL_OBJ... |
| 448,728,301 | 21 | 21,368,014.33 | -0.23 | 10698.43 | 43934.26 | 24gvfb62gt1yd | JDBC Thin Client | select sum(temp.MidUser) total... |
| 386,047,329 | 24 | 16,085,305.38 | -0.20 | 9286.27 | 45034.84 | fx8tp01tpwgkq | JDBC Thin Client | select sum(temp.MidUser) total... |
| 294,571,906 | 13 | 22,659,377.38 | -0.15 | 7002.73 | 26477.59 | 383ut78zg00hq | JDBC Thin Client | select sum(temp.MidUser) total... |
| 274,341,527 | 14 | 19,595,823.36 | -0.14 | 6415.83 | 26625.21 | cqhbuuz14x7gh | JDBC Thin Client | select sum(temp.MidUser) total... |
| 176,633,305 | 10 | 17,663,330.50 | -0.09 | 4160.82 | 26360.28 | 9xc9701y82st9 | JDBC Thin Client | select sum(temp.MidUser) total... |
一次是数据库服务器IO负载已经达到极限
SQL ordered by Reads 去磁盘取数据，单位是次，如果太大，IO会导致整个数据库慢，是RAC的环境，可能会导致数据库重启。Oracle 通过AWR的SQL ordered by Gets和SQL ordered by Reads
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原文地址：http://blog.csdn.net/stevendbaguo/article/details/45690925
