Hi @HuJiaJun(Cary)
I'm glad that you were able to resolve your issue and thank you for posting your solution so that others experiencing the same thing can easily reference this! Since the Microsoft Q&A community has a policy that "The question author cannot accept their own answer. They can only accept answers by others ", I'll repost your solution in case you'd like to "Accept " the answer.
Issue:
Recently, We noticed the SQL data base DTU has been High for a long time:
We noticed the activity log shows there is an anonymous user exports exist database every week:
What is that? Is the database backup action? How can I reduce the DTU usage?
Solution:
The problem is our marketing team is running some scan for the site, so the database cost too much.
Please remember to "Accept Answer" if any answer/reply helped, so that others in the community facing similar issues can easily find the solution.