latch: row cache objects等待事件分析

AWR Report shows contention for 'row cache objects' as the top wait:

Top 5 Timed Foreground Events

Event                    Waits      Time(s) Avg wait (ms)  DB time Wait Class
latch: row cache objects 58,291,873 130,700             2    63.18 Concurrency
DB CPU                       60,563   29.27  
db file sequential read   2,994,299  14,461             5     6.99 User I/O
library cache lock            3,179   1,662           523     0.80 Concurrency
gc cr grant 2-way         1,233,503     981             1     0.47 Cluster


对于latch相关的等待事件，我们可用通过awr的Latch Miss Sources发现在那个资源上有问题。

 Latch Name        Where	         NoWait Misses Sleeps     Waiter Sleeps
...
 row cache objects kqrpre: find obj                  0 10,332,326     8,906,124
 row cache objects kqreqd: reget                     0  7,888,165     8,503,625
 row cache objects kqreqd                            0  7,677,074     8,489,832
 row cache objects kqrso                             0      4,127         3,622
 row cache objects kqrpre: init complete             0        143            88

mos搜索where条件获取有用的信息。