等待事件：enq: SQ
阿新 • • 發佈：2019-01-04
Top 10 Foreground Events by Total Wait Time
| Event | Waits | Total Wait Time (sec) | Wait Avg(ms) | % DB time | Wait Class |
|---|---|---|---|---|---|
| enq: SQ - contention | 259 | 87.7K | 338548 | 23.3 | Configuration |
| buffer busy waits | 6,413 | 69.9K | 10900 | 18.6 | Concurrency |
| enq: HW - contention | 1,780 | 63.5K | 35669 | 16.9 | Configuration |
| DB CPU | 11.7K | 3.1 | |||
| gc buffer busy acquire | 15,486 | 6112.9 | 395 | 1.6 | Cluster |
| SQL*Net message from dblink | 12,255,704 | 4795.8 | 0 | 1.3 | Network |
| db file scattered read | 771,893 | 2263.7 | 3 | .6 | User I/O |
| gc current request | 3 | 1720.8 | 573601 | .5 | Cluster |
| SQL*Net break/reset to client | 5,089,961 | 1307.7 | 0 | .3 | Application |
| db file sequential read | 677,223 | 928.9 | 1 | .2 | User I/O |
enq: SQ - contention
在記憶體上快取(cache)範圍內，呼叫sequence.nextval期間擁有此鎖，賦予了cache+noorder 屬性的sequence上發生。
select to_char(SAMPLE_TIME,'YYYY-MM-DD HH24:MI'),event,count(1)
from dba_hist_active_sess_history where snap_id between xxx and xx
and instance_number=1 and event='latch free'
group by to_char(SAMPLE_TIME,'YYYY-MM-DD HH24:MI'),event
order by 1;
select to_char(SAMPLE_TIME,'YYYY-MM-DD HH24:MI') st ,sql_id,event,program,p1,p2,p3
from dba_hist_active_sess_history
where snap_id between xxx and xxxx and instance_number=1 and program like '%LCK%';
http://blog.csdn.net/lqx0405/article/details/46332283