We are experiencing problems with a heavily-used site where the Virtualmin backups are causing database performance to be so low that the web site becomes inaccessible during the backup. System load and memory utilization are not too high during the backup. It appears that the problem is due to the use of the mysqldump command to backup the database. This command locks the tables by default and apparently has performance issues with large databases. Fortunately, there is an alternative: mysqlhotcopy. Please consider adding an option to use this utility instead of mysqldump when doing database backups either with the MySQL Webmin module or with the backup feature in Virtualmin. Here are more details from the current MySQL documentation:
4.6.8. mysqlhotcopy
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