You Might Not Need a CRDT: Document Sync in the Wild by Paul Butler

Summary

In this presentation, the speaker demonstrates how to build a multiplayer word game using WebAssembly, focusing on determinism and state synchronization between clients and servers. By leveraging WebAssembly, the game ensures identical logic across all clients and servers, including consistent random number generation. The speaker compares the use of state machines with CRDTs (Conflict-free Replicated Data Types) in multiplayer systems, advocating for state machines due to their simplicity and reliability. They conclude with an invitation to a future event and encourage Rust engineers to connect.

Takeaways

• 😀 The speaker emphasizes the importance of web assembly (WASM) for running consistent state machines on both the client and server in multiplayer applications.
• 😀 By using WASM, the game ensures deterministic behavior, even with random elements like letter draws, which are synchronized across all clients.
• 😀 The concept of a 'state machine' is central to the speaker's approach, allowing consistent game state across all connected clients without complex data reconciliation.
• 😀 CRDTs (Conflict-free Replicated Data Types) are often thought of as necessary for multiplayer systems, but the speaker argues they are not always required for consistency.
• 😀 The speaker highlights how even randomness can be deterministic when managed by a shared state machine, ensuring all clients draw the same random letter.
• 😀 A key benefit of using deterministic state machines is that as long as the same operations are executed in the same order on every machine, the result will be consistent.
• 😀 The event sourcing approach, where system states are derived from events, has been widely adopted but is underexplored in multiplayer systems with deterministic state machines.
• 😀 The speaker’s game, created during the pandemic, runs on the principle of synchronized state transitions without needing to expose what letter was drawn—only the event of the transition.
• 😀 WebAssembly enables not just client-server synchronization, but also a unified way of managing game state without requiring complex backend infrastructure.
• 😀 The speaker invites Rust engineers to join their growing team, emphasizing the use of Rust in their development and the team's plans to expand.

Q & A

What is the main focus of the presentation?

The presentation focuses on how to design multiplayer games that synchronize across multiple clients and servers using state machines and WebAssembly, rather than relying on traditional approaches like CRDTs.

How does the multiplayer game mentioned in the transcript ensure synchronization between clients and servers?

The game ensures synchronization by running the same deterministic state machine on both the client and server. Changes, such as selecting a letter or drawing a random letter, are processed using the same logic on all devices involved.

What role does WebAssembly play in the game’s architecture?

WebAssembly allows the game to run the same module on both the client and server, ensuring that operations are deterministic and synchronized, even when random events (like letter draws) occur.

What does it mean that the game’s random letter draws are deterministic?

It means that the random number generator used for letter selection produces the same result across all clients and the server, ensuring consistency and fairness in the game, regardless of network latency or the timing of operations.

Why are CRDTs not always necessary for multiplayer games, according to the speaker?

The speaker emphasizes that CRDTs, while useful for certain applications, are not required for all multiplayer games. Deterministic state machines, like the one used in the word game, can provide consistent results across multiple clients without the complexity of CRDTs.

How does the game handle user interactions, such as selecting or unselecting letters?

User interactions, like selecting or unselecting letters, trigger state transitions that are communicated to both the server and other clients. These transitions ensure that all players see the same game state and results.

What is the significance of the 'state' in the game’s design?

The state in the game includes all necessary information to maintain synchronization, including the random number generator state and any actions taken by players. This state is sent across all clients and the server to ensure consistency.

Why is the speaker advocating for state machines in multiplayer game development?

The speaker believes state machines offer a simple, powerful, and deterministic way to synchronize game states across multiple clients. They provide an effective solution without the need for complex mechanisms like CRDTs.

What is the speaker’s perspective on the event sourcing community in relation to multiplayer gaming?

The speaker acknowledges that event sourcing and state machines have been explored by certain software engineering communities but suggests that their potential in multiplayer gaming remains underexplored, particularly for synchronizing game states.

What can attendees expect from the next browser Tech Meetup mentioned in the presentation?

Attendees can expect more information on web technologies and possibly deeper dives into topics like multiplayer synchronization, with an emphasis on deterministic state machines and the speaker’s Rust-based work.