Re: Why dba_hist_waitclassmet_history has 0 line?

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.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/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*
> <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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