If your users are running your application as a virtualized application, chances are high they use VMWare vSphere (Hypervisor ESXi) and are using snapshots.
4D v16 R2 will automatically install a VSS writer service. VSS stands here for Volume Shadow Copy Service. When the VMWare administrator starts a snapshot, VMWare informs the guest, which informs the VSS writer, which will inform 4D Server to flush the cache and wait for one second. Then it will inform the OS that the .4DD, .4DIndx and .Journal files belong together and must be snapshot at the same time. The OS will handle this and 4D Server can continue to handle client requests. The “freeze” lasts around a second, usually not even noticed by connected users.
For our customers running client-server applications on Windows, it is possible with 4D v15 R5 to enhance the end-user experience by using the Single Sign On feature, which basically allows your end-user logged into the system to also use their 4D application without being asked to re-enter any login/password.