The 1.x Files: The Stateless Ethereum Tech Tree

I began to write down a submit that detailed a “roadmap” for Ethereum 1.x analysis and the trail to stateless Ethereum, and realized that it is not really a roadmap in any respect —— not less than not within the sense we’re used to seeing from one thing like a product or firm. The 1.x workforce, though working towards a standard aim, is an eclectic assortment of builders and researchers independently tackling intricately associated subjects. Consequently, there isn’t any “official” roadmap to talk of. It isn’t full chaos although! There may be an understood “order of operations”; some issues should occur earlier than others, sure options are mutually unique, and different work is perhaps useful however non-essential.

So what’s a greater metaphor for the best way we get to stateless Ethereum, if not a roadmap? It took me slightly bit, however I feel I’ve a great one: Stateless Ethereum is the ‘full spec’ in a tech tree.

Some readers would possibly instantly perceive this analogy. In the event you “get it”, be at liberty to skip the following few paragraphs. However when you’re not like me and do not ordinarily take into consideration the world when it comes to video video games: A tech tree is a standard mechanic in gaming that permits gamers to unlock and improve new spells, applied sciences, or expertise which might be sorted right into a free hierarchy or tree construction.

Normally there’s some kind of XP (expertise factors) that may be “spent” to amass parts within the tree (‘spec’), which in flip unlock extra superior parts. Generally it’s essential to purchase two un-related primary parts to entry a 3rd extra superior one; typically unlocking one primary talent opens up a number of new selections for the following improve. Half the enjoyable as a participant is selecting the best path within the tech trie that matches your skill, objectives, and preferences (do you purpose for full spec in Warrior, Thief, or Mage?).

That is, in surprisingly correct phrases, what we now have within the 1.x analysis room: A free hierarchy of technical topics to work on, with restricted time/experience to put money into researching, implementing, and testing. Simply as in a great RPG, expertise factors are finite: there’s solely a lot {that a} handful of succesful and motivated people can accomplish in a yr or two. Relying on the necessities of supply, it is perhaps sensible to carry off on extra bold or summary upgrades in favor of a extra direct path to the ultimate spec. Everyone seems to be aiming for a similar finish aim, however the path taken to get there’ll rely on which options find yourself being absolutely researched and employed.

Okay, so I am going to current my tough drawing of the tree, speak slightly about the way it’s organized, after which briefly go into an evidence of every improve and the way it pertains to the entire. The ultimate “full-spec” improve within the tech tree is “Stateless Ethereum”. That’s to say, a completely functioning Ethereum mainnet that helps full-state, partial-state, and zero-state nodes; that effectively and reliably passes round witnesses and state data; and that’s in precept able to proceed scaling till the bridge to Eth2.0 is constructed and able to onboard the legacy chain.

The Tech Tree

Observe: As I stated simply above, this is not an ‘official’ scheme of labor. It is my finest effort at collating and organizing the important thing options, milestones, and selections that the 1x working group should decide on in an effort to make Stateless Ethereum a actuality. Suggestions is welcome, and up to date/revised variations of this plan shall be inevitable as analysis continues.

It’s best to learn the diagram from left to proper: purple parts offered on the left aspect are ‘basic’ and should be developed or determined upon earlier than subsequent enhancements additional proper. Parts with a greenish hue are coloured so to point that they’re in some sense “bonus” gadgets — fascinating although not strictly mandatory for transition, and possibly much less concretely understood within the scope of analysis. The bigger pink shapes signify important milestones for Stateless Ethereum. All 4 main milestones should be “unlocked” earlier than a full-scale transition to Stateless Ethereum could be enacted.

The Witness Format

There was loads of discuss witnesses within the context of stateless Ethereum, so it ought to come as no shock that the primary main milestone that I am going to deliver up is a finalized witness format. This implies deciding with some certainty the construction of the state trie and accompanying witnesses. The creation of a specification or reference implementation may very well be considered the purpose at which ETH 1.x analysis “levels up”; coalescing round a brand new illustration of state will assist to outline and focus the work wanted to be carried out to achieve different milestones.

Witness Format

Binary Trie (or “trie, trie again”)

Switching Ethereum’s state to a Binary Trie construction is vital to getting witness sizes sufficiently small to be gossiped across the community with out working into bandwidth/latency points. As outlined within the final analysis name, attending to a Binary Trie would require a dedication to considered one of two mutually unique methods:

  • Progressive. Like the Ship of Theseus, the present hexary state trie woud be remodeled piece-by-piece over an extended time frame. Any transaction or EVM execution touching components of state would by this technique mechanically encode modifications to state into the brand new binary kind. This suggests the adoption of a ‘hybrid’ trie construction that may depart dormant components of state of their present hexary illustration. The course of would successfully by no means full, and could be advanced for shopper builders to implement, however would for probably the most half insulate customers and higher-layer builders from the modifications occurring beneath the hood in layer 0.

  • Clear-cut. Maybe extra aligned with the importance of the underlying trie change, a clean-cut transition technique would outline an express time-line of transition over a number of exhausting forks, compute a contemporary binary trie illustration of the state at the moment, then keep on in binary kind as soon as the brand new state has been computed. Though extra easy from an implementation perspective, a clean-cut requires coordination from all node operators, and would nearly definitely entail some (restricted) disruption to the community, affecting developer and person expertise throughout the transition. Alternatively, the method would possibly present some helpful insights for planning the extra distant transition to Eth2.

Whatever the transition technique chosen, a binary trie is the premise for the witness construction, i.e. the order and hierarchy of hashes that make up the state trie. With out additional optimization, tough calculations (January 2020) put witness sizes within the ballpark of ~300-1,400 kB, down from ~800-3,400 kB within the hexary trie construction.

Code Chunking (merkleization)

One main element of a witness is accompanying code. With out code chunking, A transaction that contained a contract name would require the total bytecode of that contract in an effort to confirm its codeHash. That may very well be loads of information, relying on the contract. Code ‘merkleization’ is a technique of splitting up contract bytecode in order that solely the portion of the code referred to as is required to generate and confirm a witness for the transaction. That is one strategy of dramatically decreasing the typical dimension of witnesses. There are two methods to separate up contract code, and for the second it isn’t clear the 2 are mutually unique.

  • “Static” chunking. Breaking contract code up into fastened sizes on the order of 32 bytes. For the merkleized code to run appropriately, static chunks additionally would wish to incorporate some additional meta-data together with every chunk.
  • “Dynamic” chunking. Breaking contract code up into chunks primarily based on the content material of the code itself, cleaving at particular directions (JUMPDEST) contained therein.

At first blush, the “static” strategy in code chunking appears preferable to keep away from leaky abstractions, i.e. to forestall the content material of the merkleized code from affecting the lower-level chunking, as would possibly occur within the “dynamic” case. That stated, each choices have but to be completely examined and due to this fact each stay in consideration.

ZK witness compression

About 70% of a witness is hashes. It is perhaps attainable to make use of a ZK-STARK proofing approach to compress and confirm these intermediate hashes. As with loads of zero-knowledge stuff lately, precisely how that might work, and even that it might work in any respect shouldn’t be well-defined or simply answered. So that is in some sense a side-quest, or non-essential improve to the principle tech improvement tree.

EVM Semantics

We have touched briefly on “leaky abstraction” avoidance, and it’s most related for this milestone, so I will take slightly detour right here to elucidate why the idea is essential. The EVM is an abstracted element a part of the larger Ethereum protocol. In principle, particulars about what’s going on contained in the EVM shouldn’t have any impact in any respect on how the bigger system behaves, and modifications to the system outdoors of the abstraction shouldn’t have any impact in any respect on something inside it.

In actuality, nevertheless, there are specific points of the protocol that do immediately have an effect on issues contained in the EVM. These manifest plainly in fuel prices. A sensible contract (contained in the EVM abstraction) has uncovered to it, amongst different issues, fuel prices of varied stack operations (outdoors the EVM abstraction) via the GAS opcode. A change in fuel scheduling would possibly immediately have an effect on the efficiency of sure contracts, but it surely is dependent upon the context and the way the contract makes use of the data to which it has entry.

Due to the ‘leaks’, modifications to fuel scheduling and EVM execution must be made rigorously, as they may have unintended results on sensible contracts. That is only a actuality that should be handled; it’s extremely troublesome to design methods with zero abstraction leakage, and in any occasion the 1.x researchers haven’t got the luxurious of redesigning something from the bottom up — They should work inside at the moment’s Ethereum protocol, which is only a wee bit leaky within the ol’ digital state machine abstraction.

Returning to the principle matter: The introduction of witnesses will require modifications to fuel scheduling. Witnesses must be generated and propagated throughout the community, and that exercise must be accounted for in EVM operations. The subjects tied to this milestone should do with what these prices and incentives are, how they’re estimated, and the way they are going to be carried out with minimal impression on greater layers.

EVM Semantics

Witness Indexing / Fuel accounting

There may be probably far more nuance to this part than can fairly slot in just a few sentences; I am positive we’ll dive a bit deeper at a later date. For now, perceive that each transaction shall be chargeable for a small a part of the total block’s witness. Producing a block’s witness includes some computation that shall be carried out by the block’s miner, and due to this fact might want to have an related fuel price, paid for by the transaction’s sender.

As a result of a number of transactions would possibly contact the identical a part of the state, it is not clear one of the best ways to estimate the fuel prices for witness manufacturing on the level of transaction broadcast. If transaction house owners pay the total price of witness manufacturing, we are able to think about conditions wherein the identical a part of a block witness is perhaps paid for a lot of occasions over by ‘overlapping’ transactions. This is not clearly a foul factor, thoughts you, but it surely introduces actual modifications to fuel incentives that must be higher understood.

Regardless of the related fuel prices are, the witnesses themselves might want to turn out to be part of the Ethereum protocol, and certain might want to included as an ordinary a part of every block, maybe with one thing as easy as a witnessHash included in every block header.

UNGAS / Versionless Ethereum

It is a class of upgrades largely orthogonal to Stateless Ethereum that should do with fuel prices within the EVM, and patching up these abstraction leaks I discussed. UNGAS is brief for “unobservable gas”, and it’s a modification that might explicitly disallow contracts from utilizing the GAS opcode, to ban any assumptions about fuel price from being made by sensible contract builders. UNGAS is a part of numerous strategies from the Ethereum core paper to patch up a few of these leaks, making all future modifications to fuel scheduling simpler to implement, together with and particularly modifications associated to witnesses and Stateless Ethereum.

State Availability

Stateless Ethereum shouldn’t be going to dispose of state solely. Fairly, it should make state an elective factor, permitting shoppers a point of freedom with regard to how a lot state they hold monitor of and compute themselves. The full state due to this fact should be made accessible someplace, in order that nodes seeking to obtain a part of all the state might accomplish that.

In some sense, present paradigms like quick sync already present for this performance. However the introduction of zero-state and partial-state nodes complicates issues for brand spanking new nodes getting in control. Proper now, a brand new node can anticipate to obtain the state from any wholesome friends it connects to, as a result of all nodes make a copy of the present state. However that assumption goes out the window if a few of friends are doubtlessly zero-state or partial-state nodes.

The pre-requisites for this milestone should do with the methods nodes sign to one another what items of state they’ve, and the strategies of delivering these items reliably over a consistently altering peer-to-peer community.

State Availability

Community Propagation Guidelines

This diagram under represents a hypothetical community topology that might exist in stateless Ethereum. In such a community, nodes will want to have the ability to place themselves based on what components of state they wish to hold, if any.


Enhancements comparable to EIP #2465 fall into the overall class of community propagation guidelines: New message varieties within the community protocol that present extra details about what data nodes have, and outline how that data is handed to different nodes in doubtlessly awkward or restricted community topologies.

Information Supply Mannequin / DHT routing

If enhancements just like the message varieties described above are accepted and carried out, nodes will be capable of simply inform what components of state are held by linked friends. What if not one of the linked friends have a wanted piece of state?

Information supply is a little bit of an open-ended drawback with many potential options. We might think about turning to extra ‘mainstream’ options, making some or all the state accessible over HTTP request from a cloud server. A extra bold answer could be to undertake options from associated peer-to-peer information supply schemes, permitting requests for items of state to be proxied via linked friends, discovering their right locations via a Distributed Hash Table. The two extremes aren’t inherently incompatible; Porque no los dos?

State tiling

One strategy to bettering state distribution is to interrupt the total state into extra manageable items (tiles), saved in a networked cache that may present state to nodes within the community, thus lightening the burden on the total nodes offering state. The concept is that even with comparatively massive tile sizes, it’s probably that a number of the tiles would stay un-changed from block to dam.

The geth workforce has carried out some experiments which recommend state tiling is possible for bettering the provision of state snapshots.

Chain pruning

Much has been written on chain pruning already, so a extra detailed rationalization shouldn’t be mandatory. It’s price explicitly stating, nevertheless, that full nodes can safely prune historic information comparable to transaction receipts, logs, and historic blocks provided that historic state snapeshots could be made available to new full nodes, via one thing like state tiling and/or a DHT routing scheme.

Community Protocol Spec

Ultimately, the whole image of Stateless Ethereum is coming into focus. The three milestones of Witness Format, EVM Semantics, and State Availability collectively allow a whole description of a Community Protocol Specification: The well-defined upgrades that needs to be coded into each shopper implementation, and deployed throughout the subsequent exhausting fork to deliver the community right into a stateless paradigm.

We have coated loads of floor on this article, however there are nonetheless just a few odd and ends from the diagram that needs to be defined:

Formal Stateless Specification

On the finish of the day, it isn’t a requirement that the whole stateless protocol be formally outlined. It’s believable {that a} reference implementation be coded out and used as the premise for all shoppers to re-implement. However there are plain advantages to making a “formalized” specification for witnesses and stateless shoppers. This may be basically an extension or appendix that would slot in the Ethereum Yellow Paper, detailing in exact language the anticipated habits of an Ethereum stateless shopper implementation.

Beam Sync, Pink Queen’s sync, and different state sync optimizations

Sync methods aren’t major to the community protocol, however as a substitute are implementation particulars that have an effect on how performant nodes are in enacting the protocol. Beam sync and Pink Queen’s sync are associated methods for increase a neighborhood copy of state from witnesses. Some effort needs to be invested in bettering these methods and adapting them for the ultimate ‘model’ of the community protocol, when that’s determined and carried out.

For now, they’re being left as ‘bonus’ gadgets within the tech tree, as a result of they are often developed in isolation of different points, and since particulars of their implementation rely on extra basic selections like witness format. Its price noting that these extra-protocol subjects are, by advantage of their independence from ‘core’ modifications, a great automobile for implementing and testing the extra basic enhancements on the left aspect of the tree.

Wrapping up

Nicely, that was fairly an extended journey! I hope that the subjects and milestones, and common concept of the “tech tree” is useful in organizing the scope of “Stateless Ethereum” analysis.

The construction of this tree is one thing I hope to maintain up to date as issues progress. As I stated earlier than, it is not an ‘official’ or ‘ultimate’ scope of labor, it is simply probably the most correct sketch we now have in the intervening time. Please do attain out you probably have strategies on the way to enhance or amend it.

As at all times, you probably have questions, requests for brand spanking new subjects, or wish to take part in stateless Ethereum analysis, come introduce your self on, and/or attain out to @gichiba or @JHancock on twitter.

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