cache last heartbeat list in memory

server/client.js

@@ -33,13 +33,14 @@ async function sendNotificationList(socket) {
 async function sendHeartbeatList(socket, monitorID, toUser = false, overwrite = false) {
     const timeLogger = new TimeLogger();
 
-    let list = await R.find("heartbeat", `
-        monitor_id = ?
-        ORDER BY time DESC
-        LIMIT 100
-    `, [
-        monitorID,
-    ])
+    let monitor = userMonitorList.getMonitor(socket.userID, monitorID);
+
+    if (! monitor) {
+        console.error("No this monitor??");
+        return;
+    }
+
+    let list = monitor.getCachedHeartbeatList().array;
 
     let result = [];