Remote procedure calls in Unity - Performance & Optimization

Performance: Remote procedure calls

MEDIUM IMPACT

Remote procedure calls affect network latency and responsiveness in multiplayer or distributed Unity applications.

Sending frequent updates for player position in a multiplayer game

Unity

void Update() {
  if (Time.time - lastSent > 0.1f) {
    CmdSendPosition(transform.position);
    lastSent = Time.time;
  }
}

[Command]
void CmdSendPosition(Vector3 pos) {
  RpcUpdatePosition(pos);
}

[ClientRpc]
void RpcUpdatePosition(Vector3 pos) {
  transform.position = pos;
}

Limits RPC calls to 10 times per second, reducing network load.

📈 Performance GainReduces network traffic by 90%, improving responsiveness.

Sending frequent updates for player position in a multiplayer game

Unity

void Update() {
  CmdSendPosition(transform.position);
}

[Command]
void CmdSendPosition(Vector3 pos) {
  RpcUpdatePosition(pos);
}

[ClientRpc]
void RpcUpdatePosition(Vector3 pos) {
  transform.position = pos;
}

Sending RPC every frame causes excessive network traffic and delays.

📉 Performance CostTriggers high network latency and bandwidth usage, causing input lag.

Performance Comparison

Pattern	Network Calls	Latency Impact	Bandwidth Usage	Verdict
Send RPC every frame	High (60+ per second)	High latency and lag	High bandwidth usage	[X] Bad
Send RPC at fixed intervals	Low (10 per second)	Lower latency	Reduced bandwidth usage	[OK] Good

Rendering Pipeline

RPCs do not directly affect rendering but impact game responsiveness by delaying state updates across clients.

→Network Transmission

→Game State Update

→Rendering indirectly

⚠️ BottleneckNetwork Transmission latency

Optimization Tips

1Avoid sending RPCs every frame; use fixed intervals instead.

2Keep RPC payloads as small as possible to reduce bandwidth.

3Use Unity's Network Profiler to monitor and optimize RPC usage.

Performance Quiz - 3 Questions

What is the main performance issue with sending RPCs every frame in Unity multiplayer?

A It causes excessive network traffic and latency.

B It increases CPU usage on the client only.

C It reduces the frame rate of the local player.

D It causes memory leaks in the game.

DevTools: Network Profiler

How to check: Open Unity Profiler, select Network section, and monitor RPC call frequency and data size during gameplay.

What to look for: Look for high RPC call counts and large payloads causing spikes in network usage.

Practice

1. What attribute do you use in Unity to make a method run on the server when called from a client?

easy

A. [ServerRpc]

B. [ClientRpc]

C. [RunOnServer]

D. [RemoteCall]

Solution

1. Step 1: Understand the direction of the call

   Client-to-server calls require a special attribute to mark the method that runs on the server.

2. Step 2: Identify the correct attribute in Unity

   Unity uses [ServerRpc] to mark methods that clients call to run on the server.

3. Final Answer:

   [ServerRpc] -> Option A

4. Quick Check:

   Client-to-server calls use [ServerRpc] [OK]

Hint: Client calls server methods with [ServerRpc] attribute [OK]

Common Mistakes:

• Confusing [ClientRpc] as client-to-server
• Using non-existent attributes like [RunOnServer]
• Thinking [RemoteCall] is a valid Unity attribute

2. Which of the following is the correct syntax to declare a server RPC method in Unity?

easy

A. public void MyMethod() { }

B. [ServerRpc] public void MyMethod() { }

C. [ClientRpc] public void MyMethod() { }

D. void [ServerRpc] MyMethod() { }

Solution

1. Step 1: Recall the attribute placement

   Attributes in C# go before the method declaration.

2. Step 2: Check the correct attribute and syntax

   The correct syntax is [ServerRpc] public void MyMethod() { }. void [ServerRpc] MyMethod() { } places the attribute incorrectly.

3. Final Answer:

   [ServerRpc] public void MyMethod() { } -> Option B

4. Quick Check:

   Attributes precede method declarations [OK]

Hint: Attributes go before method signature in C# [OK]

Common Mistakes:

• Placing attribute after method name
• Using [ClientRpc] for server RPC
• Omitting the attribute entirely

3. Consider this Unity code snippet:

[ServerRpc]
public void SendMessageToClients(string msg) {
    Debug.Log("Server received: " + msg);
    BroadcastMessageClientRpc(msg);
}

[ClientRpc]
void BroadcastMessageClientRpc(string message) {
    Debug.Log("Client received: " + message);
}

What will be printed on the client when SendMessageToClients("Hello") is called from a client?

medium

A. Server received: Hello
Client received: Hello

B. Server received: Hello

C. Client received: Hello

D. Nothing is printed on client

Solution

1. Step 1: Understand the call flow

   The client calls SendMessageToClients which runs on the server due to [ServerRpc]. The server logs "Server received: Hello".

2. Step 2: Server calls client method

   The server then calls BroadcastMessageClientRpc on all clients, which logs "Client received: Hello" on each client.

3. Final Answer:

   Client received: Hello -> Option C

4. Quick Check:

   ClientRpc runs on clients, so clients see "Client received: Hello" [OK]

Hint: Client sees ClientRpc logs, server sees ServerRpc logs [OK]

Common Mistakes:

• Thinking server logs appear on client
• Assuming both logs print on client
• Confusing which method runs where

4. What is wrong with this Unity RPC method?

[ServerRpc]
public void UpdateScoreClientRpc(int score) {
    Debug.Log("Score updated: " + score);
}

medium

A. [ServerRpc] methods must be private

B. Missing return type for RPC method

C. RPC methods cannot have parameters

D. Method name suggests client RPC but uses [ServerRpc] attribute

Solution

1. Step 1: Analyze method name and attribute

   The method name contains "ClientRpc" but the attribute is [ServerRpc], which is confusing and likely a mistake.

2. Step 2: Check RPC method rules

   RPC methods can have parameters and must have a return type (void is valid). They can be public. The mismatch between name and attribute is the main issue.

3. Final Answer:

   Method name suggests client RPC but uses [ServerRpc] attribute -> Option D

4. Quick Check:

   Method name and attribute must match RPC direction [OK]

Hint: Match method name with RPC attribute to avoid confusion [OK]

Common Mistakes:

• Ignoring method name and attribute mismatch
• Thinking parameters are not allowed
• Assuming RPC methods must be private

5. You want to send a message from the server to all clients except the one who sent the original request. Which approach using Unity RPCs is correct?

hard

A. Use [ClientRpc] with a special NetworkConnection parameter to exclude sender

B. Use [ServerRpc] to send message to clients except sender

C. Use [ClientRpc] and check inside the client to ignore messages from itself

D. Use [ClientRpc] with a parameter to exclude the sender client inside the method

Solution

1. Step 1: Understand RPC direction

   Server sends messages to clients using [ClientRpc]. To exclude a client, the server must know which client to exclude.

2. Step 2: Use NetworkConnection parameter

   Unity allows [ClientRpc] methods to take a NetworkConnection parameter to exclude that client from receiving the RPC.

3. Step 3: Confirm other options

   Use [ClientRpc] with a parameter to exclude the sender client inside the method is incorrect because exclusion logic cannot be done inside the client method. Use [ServerRpc] to send message to clients except sender is wrong direction. Use [ClientRpc] and check inside the client to ignore messages from itself relies on client ignoring messages, which is inefficient.

4. Final Answer:

   Use [ClientRpc] with a special NetworkConnection parameter to exclude sender -> Option A

5. Quick Check:

   Exclude sender with NetworkConnection parameter in ClientRpc [OK]

Hint: Exclude sender using NetworkConnection param in ClientRpc [OK]

Common Mistakes:

• Trying to exclude sender inside client code
• Using ServerRpc to send to clients
• Not using NetworkConnection parameter for exclusion