config: make block prefetch the default.

Remove --dcrd-block-prefetch/-P, and add --no-dcrd-block-prefetch.

config.go

@@ -157,7 +157,7 @@ type config struct {
 	DcrdServ         string `long:"dcrdserv" description:"Hostname/IP and port of dcrd RPC server to connect to (default localhost:9109, testnet: localhost:19109, simnet: localhost:19556)" env:"DCRDATA_DCRD_URL"`
 	DcrdCert         string `long:"dcrdcert" description:"File containing the dcrd certificate file" env:"DCRDATA_DCRD_CERT"`
 	DisableDaemonTLS bool   `long:"nodaemontls" description:"Disable TLS for the daemon RPC client -- NOTE: This is only allowed if the RPC client is connecting to localhost" env:"DCRDATA_DCRD_DISABLE_TLS"`
-	BlockPrefetch    bool   `long:"dcrd-block-prefetch" short:"P" description:"Pre-fetch blocks from dcrd during startup sync."`
+	NoBlockPrefetch  bool   `long:"no-dcrd-block-prefetch" description:"Disable block pre-fetch from dcrd during startup sync."`
 
 	// ExchangeBot settings
 	EnableExchangeBot bool   `long:"exchange-monitor" description:"Enable the exchange monitor" env:"DCRDATA_MONITOR_EXCHANGES"`

main.go

@@ -894,16 +894,16 @@ func _main(ctx context.Context) error {
 
 		// Use either the plain rpcclient.Client or a rpcutils.BlockPrefetchClient.
 		var bf rpcutils.BlockFetcher
-		if cfg.BlockPrefetch {
+		if cfg.NoBlockPrefetch {
+			bf = dcrdClient
+		} else {
 			pfc := rpcutils.NewBlockPrefetchClient(dcrdClient)
 			defer func() {
 				pfc.Stop()
 				log.Debugf("Block prefetcher hits = %d, misses = %d.",
 					pfc.Hits(), pfc.Misses())
 			}()
 			bf = pfc
-		} else {
-			bf = dcrdClient
 		}
 
 		// Synchronization between DBs via rpcutils.BlockGate