Can I clean the database without broking anything?

[Niko]

After few months of mailwizz use, our DB is already huge in size, is there some table that is safe to clear of old records?
One more thing, is the delivery_server_usage_log used to count quotas or I can delete old record?

 

[twisted1919]

My advice is to simply remove old campaigns you don't need. Mailwizz will then free up all the data that is related to those campaigns.

One more thing, is the delivery_server_usage_log used to count quotas or I can delete old record?

This is used for quota counting indeed, if your user groups sending quota spans for just one month, then you can safely remove all the records older than 2 months. There is also a setting in backend to automate the deletion process, you can set the number of days to keep those logs, see Backend > Settings > Cron area.