what is the different between the Share-MDT and Switch-MDT on the multicast VPN?

An MDT is used to transmit multicast data on a public network. Packets are forwarded along an MDT and are replicated at dividing points. This reduces resource consumption on the public network. MDTs established between PE devices of the same VPN include Share-MDT and Switch-MDT. When packets are forwarded along a Share-MDT, all PE devices of the corresponding VPN instance receive the packets. When packets are forwarded along a Switch-MDT, only PE devices with receivers attached in the VPN instance receive the packets. So if you not want the PE receive the multicast packets when there are no user, you can configure the Switch-MDT ; if you not have this requirement, you can use the Share-MDT