Re: Why dba_hist_waitclassmet_history has 0 line?

Thanks, Jonathan!

Your ideas is very good! Perhaps I might also found the related DDL info from dbms_metadata.get_ddl().

I need clarify why I go to check dba_hist_waitclassmet_history - I wanna check Avtive Sessions Per Wait Class from EMCC 13.5 in the last 24 hours and more old days (7 or 31 days).

Yes, I can get several data from v$waitclassmetric_history (in the last 60 minutes) and v$waitclassmetric (in the last 1 minute).

I guess Oracle might suggest we go to check dba_hist_active_sess_history if elapsed time is more than 1 hour. Because I've also noticed that I can see the historical graph of ASH analysis when clicking the each legend (such as, cpu_used or cpu_wait) from the graph (Active Sessions Per Wait Class) of EMCC 13.5.

Best Regards
Quanwen Zhao

在 2021年12月3日星期五，Jonathan Lewis <jlewisoracle_at_gmail.com> 写道：
>
> It must be a deliberate coding decision, and there may be a hidden
parameter (or call to an internal package) that changes the way Oracle access the relevant x$, but if you trace the snapshot code you can see the SQL statement that ought to populate the relevant wrh$ from the x$ table, and then see that nothing arrives there.
> Regards
> Jonathan Lewis
>
> On Sun, 28 Nov 2021 at 08:49, Quanwen Zhao <quanwenzhao_at_gmail.com> wrote:
>>
>> Hello Listeners 😊,
>> Recently I've found three important views about "v$waitclassmetric",
"v$waitclassmetric_history", and "dba_hist_waitclassmet_history". Here're the corresponding links from oracle online docs:
>>

https://docs.oracle.com/en/database/oracle/oracle-database/19/refrn/V-WAITCLASSMETRIC.html
>>
>>

https://docs.oracle.com/en/database/oracle/oracle-database/19/refrn/V-WAITCLASSMETRIC_HISTORY.html#GUID-854BB495-19FC-4EB4-A81C-4D0EEA13B83C
>>
>>

https://docs.oracle.com/en/database/oracle/oracle-database/19/refrn/DBA_HIST_WAITCLASSMET_HISTORY.html#GUID-A931DFBF-4023-41F0-A333-E56741DE589D
>>
>> Quoted the brief introduction for themselves:
>>>
>>> 9.131 V$WAITCLASSMETRIC
>>>
>>> V$WAITCLASSMETRIC displays metric values of wait classes for the most
recent 60-second interval. A history of the last one hour will be kept in the system.
>>
>>
>>>
>>> 9.132 V$WAITCLASSMETRIC_HISTORY
>>>
>>> V$WAITCLASSMETRIC_HISTORY displays metric values of wait classes for
all intervals in the last one hour.
>>>
>>> The columns for V$WAITCLASSMETRIC_HISTORY are the same as those
for V$WAITCLASSMETRIC.
>>>
>>> 5.84 DBA_HIST_WAITCLASSMET_HISTORY
>>>
>>> DBA_HIST_WAITCLASSMET_HISTORY displays the history of the wait event
class metric data kept by the Workload Repository.
>>
>> But why dba_hist_waitclassmet_history has 0 line? Here's my query from
oracle 21.3 (test db) and found all the same situation from 19.3 and 11.2.0.4:
>>>
>>> 16:43:23 SYS_at_ORACDB> select count(*) from v$waitclassmetric;
>>>
>>> COUNT(*)
>>> ----------
>>> 13
>>>
>>> 16:43:29 SYS_at_ORACDB> select count(*) from v$waitclassmetric_history;
>>>
>>> COUNT(*)
>>> ----------
>>> 793
>>>
>>> 16:43:33 SYS_at_ORACDB> select count(*) from dba_hist_waitclassmet_history;
>>>
>>> COUNT(*)
>>> ----------
>>> 0
>>
>> Has anybody else encountered it? Oracle hasn't saved the historical
wait class metric to view dba_hist_waitclassmet_history or is it a bug?
>> Best Regards
>> Quanwen Zhao

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