Streams AQ: qmn coordinator waiting for slave to start 等待事件很少见到，今天在查看一个客户的AWR报告中发现了这个等待事件，AWR报告的TOP如下：
| Event |
Waits |
Time(s) |
Avg wait (ms) |
% DB time |
Wait Class |
| DB CPU |
|
308 |
|
62.85 |
|
| db file sequential read |
92,033 |
96 |
1 |
19.60 |
User I/O |
| db file scattered read |
44,852 |
90 |
2 |
18.39 |
User I/O |
| Streams AQ: qmn coordinator waiting for slave to start |
3 |
16 |
5269 |
3.23 |
Other |
| gc cr grant 2-way |
60,943 |
11 |
0 |
2.27 |
Cluster |
查看了用户的 aq_tm_processes参数为0，数据库版本为10.2.0.5（oracle是不建议将aq_tm_processes设置为0的),那说明此时oracle在自动分配slave进程时时存在问题的，效率过低，所以如果出现 Streams AQ: qmn coordinator waiting for slave to start等待事件，还是建议 将 aq_tm_processes 参数设置为非零值，让oracle预先分配几个slave进程， 该参数的取值范围是0~10，或者取消 aq_tm_processes 参数的设置，让oracle自动分配 。
可以通过下面的代码查看 QMON自动调整是否启用，同时 aq_tm_processes参数是否被设置为0：
- connect / as sysdba
-
- set serveroutput on
-
- declare
- mycheck number;
- begin
- select 1 into mycheck from v$parameter where name = 'aq_tm_processes' and value = '0' and (ismodified != 'FALSE' OR isdefault = 'FALSE');
- if mycheck = 1 then
- dbms_output.put_line('The parameter ''aq_tm_processes'' is explicitly set to 0!');
- end if;
- exception when no_data_found then
- dbms_output.put_line('The parameter ''aq_tm_processes'' is not explicitly set to 0.');
- end;
- /
- connect / as sysdba
- alter system reset aq_tm_processes scope=spfile sid=\'*\';
