Why dba_hist_waitclassmet_history has 0 line?

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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