Why dba_hist_waitclassmet_history has 0 line?

  • From: Quanwen Zhao <quanwenzhao@xxxxxxxxx>
  • To: ORACLE-L <oracle-l@xxxxxxxxxxxxx>
  • Date: Sun, 28 Nov 2021 16:48:53 +0800

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@ORACDB> select count(*) from v$waitclassmetric;

  COUNT(*)
----------
        13

16:43:29 SYS@ORACDB> select count(*) from v$waitclassmetric_history;

  COUNT(*)
----------
       793

16:43:33 SYS@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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