一般情况下无法从动态视图(v$session/v$session_wait)看到这个等待事件，因为它十分短暂。其本质从字面意思上来解释的话，是一种网络等待(network issue)；
举例而言，如果运行的代码中包含某种可能的错误，且在调用中触发了的话，服务器端本地的服务进程有义务对远程客户端告知该信息，这个告知的过程中服务进程就处于SQL*Net break/reset to client等待中，直到客户端收到问题信息为止。与一般意义上的Sever-client模式一样，使用dblink时也可能出现该种等待事件。
下面我们来尝试演示该种等待事件：
SQL> create table tv (t1 int unique); Table created. SQL> insert into tv values(1); 1 row created. SQL> commit; Commit complete. SQL> oradebug setmypid; Statement processed. SQL> oradebug event 10046 trace name context forever,level 8; Statement processed. SQL> insert into tv values(1); insert into tv values(1) * ERROR at line 1: ORA-00001: unique constraint (SYS.SYS_C009343) violated SQL> oradebug event 10046 trace name context off; Statement processed. SQL> select event, total_waits from v$session_event where event like '%break%' and sid =(select distinct sid from v$mystat); EVENT TOTAL_WAITS ---------------------------------------------------------------- ----------- SQL*Net break/reset to client 2
可以看到出现了2次SQL*Net break/reset to client ,进一步分析trace文件可以发现以下记录:
EXEC #2:c=8000,e=9020,p=0,cr=10,cu=9,mis=0,r=0,dep=0,og=1,plh=0,tim=1279117896316991 ERROR #2:err=1 tim=1279117896317039 STAT #2 id=1 cnt=0 pid=0 pos=1 obj=0 op='LOAD TABLE CONVENTIONAL (cr=0 pr=0 pw=0 time=0 us)' WAIT #2: nam='SQL*Net break/reset to client' ela= 33 driver id=1413697536 break?=1 p3=0 obj#=-1 tim=1279117896317323 WAIT #2: nam='SQL*Net break/reset to client' ela= 521 driver id=1413697536 break?=0 p3=0 obj#=-1 tim=1279117896317915 WAIT #2: nam='SQL*Net message to client' ela= 5 driver id=1413697536 #bytes=1 p3=0 obj#=-1 tim=1279117896317964
2次SQL*Net break/reset to client分别为33us和521us; 设计不良的应用程序或者程序中存在较多未安置的exception都可能导致SQL*Net break/reset to client等待事件。
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