# Why Dapp Users Will Hate Cross-Shard Communication (and What You Can Do About It) - Devcon5

- Channel: [Devcon](https://streameth.org/devcon)
- Date: 2020-10-09
- Duration: 09:23
- Topics: blockchain, smart contracts, distributed ledger, Science & Technology
- Watch: https://streameth.org/watch/yt-1dmPPRkow_c
- YouTube: https://www.youtube.com/watch?v=1dmPPRkow_c

## Description

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https://archive.devcon.org/archive/watch/5/why-dapp-users-will-hate-cross-shard-communication-and-what-you-can-do-about-it

ETH2 is approaching, and initial indications are that substantially all dapp experiences will suffer. Some problems may be addressed with significant changes to design and development processes, but several tradeoffs are unavoidable without sacrificing scale, security, or decentralization. For example, essentially all popular dapps rely on the fungibility of Ether in a managed pool (e.g. Uniswap, Augur, Maker). In a sharded ecosystem, Ether is meaningfully non-fungible across shards, and users will bear monetary and management costs as a result.This talk will give an overview of cross-shard communication strategies and discuss their impact on developer and user experience. These include merged consensus, shard relays, consensus introspection, and credit markets. For each mechanism, we'll discuss expected impact on user experience metrics like execution time, transaction outcome, and price slippage.The talk is not all bad news. We've discovered some elegant new approaches that give dapps a variety of communication choices. The last section of the talk will discuss specific communication strategies that are amenable to specifi

Speaker(s): James Prestwich
Skill level: Intermediate
Track: Consensus layer
Keywords: technical

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Devcon 5 was held in Osaka, Japan on Oct 8 - 11, 2019.
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## Transcript

[Applause] making traditions about the subjective futures date of a remote shame it's complex it's a little redirect event around but it might actually be possible in princess another alternative is just to let the pre-market solve your problem so if I want to send a message to a I could add someone else send that message on a on that using their own money and then pay them back they've been back using the crusher communication via another mechanism so for example if you have money on a I could pay you slow cross charge F in order to put up your money immediately so you could revitalize my CDP for me and then I will think about what F that comes through slow so I would be chopping up my CEP by entering into a new debt to someone else there's a couple like pros here it's instant the cons are that it's incredibly complex implementer relies on Rancher market actors just showing up you're gonna have to pay some amount of spread because they're giving us the quiddity on your behalf even though they have a strong guarantee that you will pay them back so there's gonna be like slippage and crusher the price you pay will pay more than one shark be either for each chart a new frequency so you're gonna pay for this service right and the creditors can actually extort you a little bit depending on how this is structured they know your CTB's going to get liquidated and they know that you're going to pay up to that amount up to the amount you lose and so that the opportunity to charge you higher rates based on this case that you're transferring me for and it doesn't work for some state if there's any secrets here you can't give away private keys or hash free images that are important to your creditor so you actually can't use this for some types of contracts all right now we're getting away from things that I think could actually be easily get collected and we're getting into stuff that is a little more like Wiggly what we depending on my future research I only got a couple of these and then we're gonna break for questions for the last five minutes okay so we've talked about charts we have to do an asynchronous communication across charts the idea has been placed to synchronize charts too early so it take ambi and just move them into the same place and have a period of time where there's synchronous and I did not do a very good job on these theories don't worry about so for a period of time we're going to have sheriff validators between hand people and then anyone on a or I'm beefing interact with the other shard and instantly you know in a single transaction without any waiting period so it would let me use my Ethernet sharpie and a CD beyond charge a one of the ideas is that we free randomized these parents regularly hungry they suspend what we invented charting to fix each one part of the reason that doesn't scale is because it has the synchronous transactions is because all the contracts can interact with all the other contracts so like we wanted to sharp things to get away from this model because it prevents scale so if we do is synchronous shards or we have like synchronous periods among different sharks we're giving up a huge portion of these scaling advantages of charting for example if we pair two sharks that's five through twelve pairs so we've given up half the scale of our chain okay and then l2 state we're just gonna like very briefly touch on this because nobody has proposed that decent like commenting the model for it that I know of there's a lot of interesting ideas about moving contract state into in the plasma chains or state channels or similar constructions one of the main pushes in e2 is to have what's called stateless clients where the entire chain state of any given shard is with the that are actually using it rather than in the consensus process where we can come to consensus on updates to the group connection of the state rather than updates to the state it's a bit of a difficult concept to talk about but generally speaking this was involved taking contracts which are a sharpie and either proposal and putting them into a shared layer tree system that could settle for those charts we don't know what this would look like a lot of people are very excited about it and I would think that getting a concrete design is a couple years off it's okay so this is the end of my slides for now do we have any questions about cross direct communication any way to kind of think about for that given that they should repeat that shops available to appeal the dial compound say hey we're we're making pretty best market richness there's 2% shopping suddenly everybody Oh same time yeah so yeah yeah you're asking whether there's a risk that contracts will want to be on the same chart as other contracts so that they can interact directly and I think there's definitely that great split one of the reasons we all got involved in the period is because we have variable smart contracts is because CDP's and compound can interact charting grapes that guarantee and makes it asynchronous interaction so you have weaker guarantees about how the interaction effects to use them so compound and maker a particularly interesting because compound relies on a shared liquidity for your compounds rate is dependent on how much of each asset is in compound right now and in a shard of ecosystem there have to be a thousand and 24 different compounds deployed with different liquidity pools so yeah there are some pretty concrete advantages to having a chain with all of the smart contracts on it unfortunately you know that's what we invented Chardon to get rid of because it prevents scale yes this newspaper you see there is ok so just any do any of these models give privacy of your data segregation across trains no today the segregation of public chain is an impossible task for a concrete example in aetherium we can always load the snake tree as a purple tree in a smart contract to inspect private state variables so any sort of unashamed public private public chain privacy is kind of an illusion we can make it more difficult to read specific state but we can't make it impossible to be in that state if you're talking about like user oriented privacy like zkp there's the cash gifts that's kind of we're talking to cross our communication it's so LCC North America on with that connects yeah all L to requires like some magic waiting period usually measured in days one of the nice things about the cross lengths is that they should finalize your mistake much quicker than that the reason we have a multi day waiting period for l2 is to provide better security for users because one of the experience options of all help to constructions is that a user can get a transaction launching in the waiting period so one hour waiting period means excess a presumption it's likely that that part of it will be much more significant than the crushed shirt communication part of said I might help you see all right where time's up come find me afterwards [Applause]