cmd, core, eth: support disabling the concurrent state prefetcher

eth/config.go

@@ -92,7 +92,9 @@ type Config struct {
 	// Protocol options
 	NetworkId uint64 // Network ID to use for selecting peers to connect to
 	SyncMode  downloader.SyncMode
-	NoPruning bool
+
+	NoPruning  bool // Whether to disable pruning and flush everything to disk
+	NoPrefetch bool // Whether to disable prefetching and only load state on demand
 
 	// Whitelist of required block number -> hash values to accept
 	Whitelist map[uint64]common.Hash `toml:"-"`