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
在内存上缓存(cache)范围内，调用sequence.nextval期间拥有此锁，赋予了cache+noorder 属性的sequence上发生。
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
