What makes a node a warp-sync node?

[phahulin]

I'm running:

• Which Parity version?: 1.9.2
• Which operating system?: Linux
• How installed?: via binaries
• Are you fully synchronized?: yes
• Which network are you connected to?: sokol
• Did you try to restart the node?: no

When connecting to our network, some nodes can be warp-synced from (you download snapshots first, then latest blocks), but others - can't (you start downloading blocks from 0). Why is it, what makes a node warp-syncable (pardon my french)? both nodes appear to be fully synced (at least they have the same height).

[5chdn]

Warp-Sync is hardly possible on Ethereum anymore as the state is growing so fast. The issue you experience is pretty much summarized on our wiki:

https://paritytech.github.io/wiki/Known-Issues-Priorities

Key issues are #7863 and #7436 here: There are not enough nodes in the network providing recent snapshots.

We are working hard on solutions, but it looks very much like the future belongs to the light clients.