adlrocha

This week has been another of those weeks where I am pretty happy with the progress made. The highlights of the week are the following: (i) we now have a pretty good sense of the end-to-end operation to commit shard segments into the global history of the beacon chain (as described in the discussion of PR267); (ii) and Nazar had an idea to tackle the verification of the availability and correctness of shard segments without requiring an independent data availability mechanism, by leveraging the longest-chain rule and farmers membership allocation (which was an issue that was really bugging me). Let’s jump into the details of these two topics.

I started the week thinking about the mechanics of shard segment commitment into the global history of the beacon chain. If you recall from previous updates, we already had a pretty good idea of how the information about child shard segments flow up to the beacon chain, but there were still a few questions that were really bugging me.

I am pretty happy with the progress this week. Funnily, the main culprit for all of this progress has been the the work that Nazar has been doing on the definition of the block structure for our hierarchical consensus. I’ll let Nazar dig deeper into what he’s been doing here, but let me share in this post what this block structure entails, and how this has unblock several lines of work, and solved many issues for me.

This week has been mainly focused on clearing the fog around shard archiving and trying to start fleshing the low-level details for the protocol. It feels like in the past few weeks we’ve been surfacing more questions than answers, and I honestly think this is a good sign. It means that we are getting to the point where we can start to see the details of the protocol and how it will work in practice.

We keep iterating on the best way to discuss and make progress on the design of the protocol. Using issues for discussions have shown less efficient than originally expected. The inability to make in-line threads, and having to quote every single detail of the spec that we want to discuss about was really cumbersome. I started the shard block submission issue as an attempt to start iterating the low-level details of specific protocol mechanisms in a way that is narrow enough and easy to track, but it didn’t fulfill all our needs. The solution? Creating discussion PRs that I don’t expect to get merged, but gives us all that we need to have low-level discussions about specific parts of the protocol, track our progress, open ideas, and discussions, and have them public so anyone can contribute or follow along.

We started last week with two PRs that attempted to describe in detail the operation of sharded archiving (PR192), and the data availability layer of the system (PR193). When I started writing this spec, it was meant to be for a broader audience, but we realised after a few rounds of feedback that the project is still in a really early stage and in constant change, so it would be more efficient to focus on detailing the parts of the protocol that are currently under-defined instead of trying to give a deep overview of the overall operation of the protocol from the get-go. The actual goal behind this protocol specification is to unblock the implementation of a prototype that can help us gain certainty about the design decisions that we are making, and surface potential blind spots in the design, and not to have a reference spec (just yet).

Over the past weeks, my updates have highlighted many of the ideas emerging from our open design discussions. Now that we have a clearer direction for the design, I wanted to consolidate these ideas into a draft spec. This will serve as a foundation for implementing the first few prototypes, while also providing a structured way to gather feedback and uncover potential blind spots. I expect this spec to suffer significant changes, but it felt like the perfect way to consolidate the ideas, get feedback from the community, and unblock Nazar in case he wants to start prototyping some of the ideas we’ve been discussing.

This week has been another good week of progress. I finally have a good idea of how shard archiving should work in the happy path, and I’ve started writing a low-level spec for it (that I am hoping to push to this repo soon). Unfortunately, there is still a slight gap in the spec that we need to fill before we can move forward: the data availability problem.

This week I’ve gone a bit deeper into the design of the multi-shard Subspace protocol idea which I briefly introduced in my last update. The protocol is conformed by the following parts: Sharded archiving, responsible for creating a global canonical history of the whole system, and of creating the history records that will eventually become part of farmers’ plots. Sharded plotting, which takes records from the global history and seals them in plots that include segments of the history of every shard of the system, and that will be used for the farming process. And finally, merged farming, which is the protocol responsible for challenging farmer plots, and deriving the corresponding winning tickets that elect block proposers in specific shards. Let me introduce the high-level operation behind each of these sub-protocols, while digging deep in the one that I’ve focused the most on this week: sharded archiving.

After a lot of thinking, this week I came to the realisation that a sharded architecture like the one we are trying to build can be designed leveraging the current design of the Subspace protocol and all its underlying mechanisms as a base. While this was the idea from the beginning, either for lack of familiarity with the protocol or plain ignorance, I was missing the big picture of how this could be done.