Why drop Table need 10 minutes?

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Why drop Table need 10 minutes?

case 1.
In batch time (22:00 ~ 09:00) batch jobs drop table used 1 second but after 09:00 user begin use the teradata database drop table used 10 minutes. I used PMON monitor these job no lock and the CPU usage same as the batch time near 94%.

case 2.
In batch time batch jobs will not lock dbc.accessrights but the same jobs after 09:00 if lock abc.accessrights then I move hight CPU Job to penalty box let the CPU usage down to 10% during two hours but these batch jobs still lock can't release.

Somebody can give me some hints. Thanks!

Best Regards

Johnson Yeh