🐛 fix: db pool limit

[lwnmengjing]

Description

Checklist

• the pull request title describes what this PR does (not a vague title like Update index.md)
• the pull request targets the default branch of the repository (main)
• no unintentional fmt.Print left behind after debugging
• did I name variables, methods and classes according to the naming rules? (https://go.dev/doc/effective_go#names)
• caught exceptions or throw them to the upper level for processing, not ignored (https://go.dev/doc/effective_go#errors)
• did I explain all possible solutions and why I chose the one I did?
• added any comments to make new functions clearer
• tests are added for the changes I made (if any source code was modified)
• documentation added or updated
• I have run the project locally and verified that there are no errors
• instructions for how reviewers can test the code locally
• screenshot of the feature/bug fix (if applicable)