On mongodb Query Performance

  mongodb, question

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What is the performance consumption of the above query?
I did a test locally, such as the data shown in the following figure, and inquired about username, about 170W

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It takes more than one second. Is this normal?

It is normal that regular expressions are just like those in SQLLIKESimilarly, unless the left side is fixed, the index cannot be used; it is a full table scan.