RAC 中MMON remote action broadcast channel

之前遇到过一次11.2.0.4.0 RAC 环境 Result Cache: Channel

这次再次遇到，

update 一条语句时，造成提交持续锁表

select * from (select sid,event,p1,p2,p3,p1text,WAIT_TIME,SECONDS_IN_WAIT from v$session_wait where wait_class# <> 6
order by wait_time desc) where rownum <=10;

RAC 中MMON remote action broadcast channel

select session_id,sql_id,sample_id,event,sample_time from v$active_session_history where session_id==&sid;

select sql_text from v$sqltext where sql_id='&sql_id' order by piece;

result cache被使用

SQL> show parameter result_cache_max_size

NAME_COL_PLUS_SHOW_PARAM TYPE
-------------------------------------------------------------------------------- -----------
VALUE_COL_PLUS_SHOW_PARAM
--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
result_cache_max_size big integer
197280K

gv$chanel_waits显示高等待的组件

SQL> set linesize 200 pagesize 500
SQL>
SQL> SELECT CHANNEL,
  2    SUM(wait_count) sum_wait_count
  3  FROM GV$CHANNEL_WAITS
  4  GROUP BY CHANNEL
  5  ORDER BY SUM(wait_count) DESC;
CHANNEL                                                          SUM_WAIT_COUNT
---------------------------------------------------------------- --------------
MMON remote action broadcast channel                                     806260
kxfp control signal channel                                              167559
RBR channel                                                               26448
obj broadcast channel                                                      5153
LCK0 ksbxic channel                                                         252
quiesce channel                                                               2
service operations - broadcast channel                                        2
kill job broadcast - broadcast channel                                        1
parameters to cluster db instances - broadcast channel                        1
9 rows selected

如果满足上面的3个条件，那么可以确定该等待事件由result cache处理相关的bug_19557279造成，该问题在Oracle 12.2版本中修复。

SOLUTION

Upgrade to a version where Bug 19557279 is fixed i.e. Oracle 12c release 12.2 or the 12.1.0.2.0 Patchset
Apply patch 18416368 if available on your platform
To workaround the issue, disable result cache by setting the following parameter:
SQL> alter system set result_cache_max_size=0;
The instance(s) must be restarted for the parameter to take effect.

调整后问题解决

SQL> SELECT CHANNEL,
2 SUM(wait_count) sum_wait_count
3 FROM GV$CHANNEL_WAITS
4 GROUP BY CHANNEL
5 ORDER BY SUM(wait_count) DESC;
CHANNEL SUM_WAIT_COUNT
---------------------------------------------------------------- --------------
kxfp control signal channel 19
MMON remote action broadcast channel 5
quiesce channel 2
service operations - broadcast channel 1