Sliding Sync at the Matrix Conference

Berlin. Saturday, September 21, 2024. 10am. I was live on stage and broadcasted on Internet, to talk about (Simplified) Sliding Sync, the next sync mechanism for Matrix, at the first Matrix Conference.

Matrix is an open network for secure, decentralised communication. It is an important technology for Internet.

Matrix is a protocol. Everyone can implement it: either by providing its own server and connect it to the federation, or by providing its own client and connect it to the federation too. Nobody has a full control over the network, and nobody controls the clients nor the servers. And yet, end-to-end encryption is working, synchronisation is working, and everybody can talk to everybody, communities organize themselves, the network grows and grows.

I am working at Element since 2 years now. I am paid to work on the [Matrix Rust SDK], a project owned by the Matrix organisation. Everything we do is available to the entire Matrix community, not only for Element. Well, this is the open source world.

Matrix previous synchronisation mechanism is slow and inefficient. To put Matrix on the hands of everyone for a daily pleasant usage, we have started to experiment with a new sync mechanism, called Sliding Sync. The MSC —which stands for Matrix Spec Changes, like RFC for example—, so the MSC3575 was our experimental foundation to play with a new sync mechanism. After many sweat and tears, we ultimately found a working pattern and design that fulfill a large majority of our usecases. Along the way, the implementation inside the Sliding Sync Proxy —a proxy that sits on the top of a homeserver¹ to provide this new sync mechanism— was starting to feel really buggy and was really slow. It was time to clean up everything, including the MSC.

Enter MSC4186, which is basically Simplified Sliding Sync. We have mostly removed features from MSC3575, so that the implementation on the server-side is much simpler and lighter. Simplified Sliding Sync is now implemented and enabled by default on Synapse, one of the major homeserver implementations. Other homeservers have implemented MSC3575 and are working on supporting MSC4186.

Sliding Sync has a huge impact on the overall user experience. Syncing is now fast and almost transparent. It also works linearly whether the user has 10 or 10'000 rooms.

My talk can be viewed here:

Other talks#

All the talks are available online, including talks from the public sector, like NATO, Sweden, French or German administrations… I encourage you to check the list! Nonetheless, I take the opportunity of this article to highlight some announcement talks, or technical (Matrix internals) talks, I've enjoyed.

Matrix 2.0 and the launch of Element X!#

Two presentations for the price of one: Matrix 2.0 Is Here! by Matthew Hogdson. 10 years after the original launch of Matrix, and 5 years after Matrix 1.0, what a best anniversary to announce Matrix 2.0.

The second video is Element X Launch! by Amandine Le Pape, Ștefan Ceriu, and Amsha Kalra. They present Element X, how it's been designed, developed, how it uses the Matrix Rust SDK, and where you can see awesome demos of Element X with Element Call and so on! It was a great moment for everyone working at Element and users!

Unable to decrypt this mesage#

Unable to decrypt this message by Kegan Dougal. This talk explains why one can see an Unable To Decrypt error while trying to view a message in Matrix. Most problems have been solved today, but the great message about this presentation is to show how hard it is (was!) to provide reliable end-to-end encryption over a federated network. One homeserver can be overused and then slowed down, or a connection between two servers can be broken, or one device lost its connectivity because it's used in the subway, or whatever. All these classes of problems are illustrated and explained. I liked it a lot because it gives a good sense of why end-to-end encryption is hard over a giant decentralised, federated network, with encryption keys being renewed frequently, and how problems have been solved.

News from the Matrix Rust SDK#

Strengthening the Base: Laying the Groundwork for a more robust Rust SDK by Benjamin Bouvier, a good friend! This talk explains the recent updates of the Matrix Rust SDK: how we have designed new API to make the developer experience easier and more robust.

About transport#

I currently live in Switzerland. The conference was in Germany. Europe has a fantastic rail network, and more importantly, a unique night train network!

Going there by plane would have generated 1'344 kg CO₂eq, be 68% of my annual carbon budget (for a sustainable world, we should all be at 2'000 kg maximum). Taking the train however has generated 6.5 kg CO₂eq, be 0.33% of my annual carbon budget. It's 206 times less than the plane!

If you are curious to try night train, you can check this map that lists all possible connections, stops, companies operating the trains etc. Taking the night train is a nice way of travelling, and it saves a lot of emissions.

I've taken a regular day train to go to Berlin, and a night train to come back home.