Does unused database hurt MySQL server performance in any way?

If there are some unu开发者_运维问答sed databases on MySQL server is it better to remove those from server?

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If they're unused then by all means remove them.

However, leaving them around shouldn't hurt day-to-day performance as they aren't referenced by any application.

They will have an impact on the server performance in areas such as backups etc. as they are more data that has to be checked and copied etc.

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Yes it CAN hurt performance because it will mean more RAM is being used and if you are low on RAM this can cause issues.

For example, lets say you have website_new and unused website_old databases. If you had innodb pool set to 3GB then you would need to increase that if the website_old is left sitting there.

Keeping old DBs around will force you to skew your my.cnf config to maintain performance.

hope this helps