insert /* KSXM:TAKE_SNPSHOT */ into sys.optstat_snapshot$

收集统计信息时，活动连接中根本看不到收集统计信息的sql，而是如下的sql_id=3wh9htctp7199
SQL_ID 3wh9htctp7199, child number 12
insert /* KSXM:TAKE_SNPSHOT */ into sys.optstat_snapshot$ (obj#,
inserts, updates, deletes, timestamp, flags) (select m.obj#, m.inserts,
m.updates, m.deletes, systimestamp,
dbms_stats_advisor.compute_volatile_flag( m.obj#, m.flags, :flags,
m.inserts, m.updates, m.deletes, s.inserts, s.updates, s.deletes,
null, nvl(to_number(p.valchar), :global_stale_pcnt), s.gather) flags
from sys.mon_mods_all$ m, (select si.obj#, max(si.inserts) inserts,
max(si.updates) updates, max(si.deletes) deletes,
decode(bitand(max(si.flags), :gather_flag), 0,
‘NO_GATHER’, ‘GATHER’) gather, max(si.timestamp) timestamp
from sys.optstat_snapshot$ si, (select obj#, max(timestamp) ts from
sys.optstat_snapshot$ group by obj#) sm where si.obj# = sm.obj# and
si.timestamp = sm.ts group by si.obj#) s, sys.optstat_user_prefs$ p
where m.obj# = s.obj#(+) and m.obj# = p.obj#(+) and pname(+) =
‘STALE_PERCENT’ and m.obj# = :objn)

Mos 2435833.1 是关于这个sql的功能介绍
The below INSERT statement is part of Optimizer Statistics Advisor which analyzes how optimizer statistics are gathered, and then makes recommendations. It is introduced in 12CR2. This job will help you in getting optimum execution plans for all the queries running in your database. There is no performance impact to the database if it executes.
此语句是Optimizer Statistics Advisor的一部分，它分析优化器统计信息是如何收集的，然后给出建议。它在12CR2中被引入。此作业将帮助您为数据库中运行的所有查询获得最佳的执行计划。如果执行的话，对数据库没有性能影响。

显然没有提升性能，反而起了反作用，怎么办呢？系统都卡在这条sql上了

–禁用掉吧
1.To check the current value for the preference:
SQL> select dbms_stats.get_prefs(‘AUTO_STATS_ADVISOR_TASK’) from dual;
DBMS_STATS.GET_PREFS(‘AUTO_STATS_ADVISOR_TASK’)
TRUE

2.disable
SQL> exec dbms_stats.set_global_prefs(‘AUTO_STATS_ADVISOR_TASK’,‘FALSE’);

不幸的是19c版本上disable时会报错，需要安装个one-off patch， Bug 26749785 One-off backport can be requested for versions like 12.2 / 18c / 19c to get this functionality.

参考：How To Disable Optimizer Statistics Advisor From 12.2 Onwards (文档 ID 2686022.1)

–purge
How To Purge Optimizer Statistics Advisor Old Records From 12.2 Onwards (文档 ID 2660128.1)

我的方法：
truncate table sys.OPTSTAT_SNAPSHOT$;

标签：insert,KSXM,obj,inserts,into,sys,si,updates,deletes
来源： https://blog.csdn.net/u010663554/article/details/112390645