Better caching during simulation

3 files changed, 27 insertions, 8 deletions

diff --git a/backend/package-lock.json b/backend/package-lock.json
index a721fb0..ccc093b 100644
--- a/backend/package-lock.json
+++ b/backend/package-lock.json
@@ -1723,9 +1723,9 @@
             }
         },
         "node_modules/qs": {
-            "version": "6.14.0",
-            "resolved": "https://registry.npmjs.org/qs/-/qs-6.14.0.tgz",
-            "integrity": "sha512-YWWTjgABSKcvs/nWBi9PycY/JiPJqOD4JA6o9Sej2AtvSGarXxKC3OQSk4pAarbdQlKAh5D4FCQkJNkW+GAn3w==",
+            "version": "6.14.2",
+            "resolved": "https://registry.npmjs.org/qs/-/qs-6.14.2.tgz",
+            "integrity": "sha512-V/yCWTTF7VJ9hIh18Ugr2zhJMP01MY7c5kh4J870L7imm6/DIzBsNLTXzMwUA3yZ5b/KBqLx8Kp3uRvd7xSe3Q==",
             "license": "BSD-3-Clause",
             "dependencies": {
                 "side-channel": "^1.1.0"
diff --git a/backend/src/database/postgres.ts b/backend/src/database/postgres.ts
index 6f6b682..e2493a9 100644
--- a/backend/src/database/postgres.ts
+++ b/backend/src/database/postgres.ts
@@ -8,7 +8,7 @@ const pool = new Pool({
     port: process.env.DB_PORT ? parseInt(process.env.DB_PORT) : 5432,
 });
 
-/* Too strict for Docker:
+/* Too strict for Docker, use docker compose healthcheck instead:
 pool.connect((error, _client, release) => {
     if (error) {
         console.error("Verbindung zur Datenbank fehlgeschlagen: ", error);
diff --git a/backend/src/simulation/robotMovementSimulator.ts b/backend/src/simulation/robotMovementSimulator.ts
index 2299f43..d3a2564 100644
--- a/backend/src/simulation/robotMovementSimulator.ts
+++ b/backend/src/simulation/robotMovementSimulator.ts
@@ -1,6 +1,7 @@
 import { QueryResult } from "pg";
 import { Server } from "socket.io";
 import db from "../database/postgres.js";
+import redisClient from "../database/redis.js";
 import {
     Robot,
     RobotPosition,
@@ -8,6 +9,9 @@ import {
     SimulationResponse,
 } from "../types/robot.js";
 
+const CACHE_TTL = 10;
+const ROBOTS_CACHE_KEY = "allMyRobots";
+
 // Coordinates for the boundaries of the frontend map
 const LEIPZIG_AREA = {
     WEST: 12.22,
@@ -70,10 +74,19 @@ async function updateRobotPositions(io: Server) {
     try {
         client = await db.connect();
 
-        const allRobotsQuery: QueryResult<Robot> = await client.query(
-            "SELECT * FROM robots ORDER BY id;"
-        );
-        const allRobots = allRobotsQuery.rows;
+	let allRobots;
+	const cachedData = await redisClient.get(ROBOTS_CACHE_KEY);
+
+	// Check Redis for cached data, otherwise query database
+	if (cachedData) {
+	    allRobots = JSON.parse(cachedData);
+	} else {
+	    const allRobotsQuery: QueryResult<Robot> = await client.query(
+		"SELECT * FROM robots ORDER BY id;"
+            );
+
+	    allRobots = allRobotsQuery.rows;
+	}
 
         // Update database
         await client.query("BEGIN");
@@ -142,6 +155,12 @@ async function updateRobotPositions(io: Server) {
 
         await client.query("COMMIT");
 
+	// Keep robots in Redis cache indefinitely while simulation is running to avoid db query on every tick
+	// Once the simulation stops, keep the cache alive for 10 seconds
+	await redisClient.set(ROBOTS_CACHE_KEY, JSON.stringify(updatedRobots), {
+	    EX: movingRobots.size === 0 ? CACHE_TTL : undefined,
+	});
+
         // Websocket broadcast, make sure robots stay in correct order
         updatedRobots.sort((a, b) => a.id - b.id);