don't delete unreachable routers if tunnel creation success rate is too low

libi2pd/NetDb.cpp

@@ -603,6 +603,7 @@ namespace data
 		uint64_t expirationTimeout = NETDB_MAX_EXPIRATION_TIMEOUT*1000LL;
 		uint64_t ts = i2p::util::GetMillisecondsSinceEpoch();
 		auto uptime = i2p::context.GetUptime ();
+		bool isLowRate = i2p::tunnel::tunnels.GetTunnelCreationSuccessRate () < NETDB_MIN_TUNNEL_CREATION_SUCCESS_RATE;
 		// routers don't expire if less than 90 or uptime is less than 1 hour
 		bool checkForExpiration = total > NETDB_MIN_ROUTERS && uptime > 600; // 10 minutes
 		if (checkForExpiration && uptime > 3600) // 1 hour
@@ -624,7 +625,7 @@ namespace data
 				continue;
 			}
 			// make router reachable back if too few routers or floodfills
-			if (it.second->IsUnreachable () && (total - deletedCount < NETDB_MIN_ROUTERS ||
+			if (it.second->IsUnreachable () && (total - deletedCount < NETDB_MIN_ROUTERS || isLowRate ||
 				(it.second->IsFloodfill () && totalFloodfills - deletedFloodfillsCount < NETDB_MIN_FLOODFILLS)))
 				it.second->SetUnreachable (false);
 			// find & mark expired routers

libi2pd/NetDb.hpp

@@ -38,6 +38,7 @@ namespace data
 {
 	const int NETDB_MIN_ROUTERS = 90;
 	const int NETDB_MIN_FLOODFILLS = 5;
+	const int NETDB_MIN_TUNNEL_CREATION_SUCCESS_RATE = 8; // in percents
 	const int NETDB_FLOODFILL_EXPIRATION_TIMEOUT = 60 * 60; // 1 hour, in seconds
 	const int NETDB_INTRODUCEE_EXPIRATION_TIMEOUT = 65 * 60;
 	const int NETDB_MIN_EXPIRATION_TIMEOUT = 90 * 60; // 1.5 hours