The Inside Scoop: Maintenance tips for your vSphere Database | VMware Support Insider - VMware Blogs
VirtualCenter Database Maintenance: SQL Server
VMware KB: Investigating the health of a vCenter Server database
VMware KB: Determining where growth is occurring in the VMware vCenter Server database
VMware KB: Shrinking the size of the vCenter Server SQL database
VMware KB: Purging old data from the database used by VMware vCenter Server 4.x and 5.x
VMware KB: Checking the status of vCenter Server performance rollup jobs