Demystifying JAM - PBA6

#polkadot #jam #pba

blog.kianenigma.com/posts/tech/demystifying-jam/

Note:

This Talk

Understand what JAM is
JAM's role in the broader Web3 vision

Understanding What JAM Is

aka. Demystifying JAM

Polkadot 1

Social
- OpenGov
- DOT Token → Security
- Fellowship
Technological
- Heterogeneous Execution Sharding, with Shared Security

Note:
Sharding enabled by the use of ELVES, and heterogeneity enabled by the use of WASM.
ELVES: Efficient Execution Auditing for Blockchains under Byzantine Assumptions

Heterogeneous Execution Sharding, with Shared Security

Let's break it down:

Execution Sharding
With Shared Security
Heterogeneous

Sequential Blockchain

Notes:

Opposite of execution sharding
How blockchains usually work

(Poorly) Execution Sharded

Sharding the validator set: less security

Execution Sharded with Shared Security

ELVES and Cynical Rollups
Core Model

Note:
Original vision of ETH 2 was to be this, with 64 shards.

Heterogeneous

WASM bytecode

Now You Get It?

Execution Sharding + With Shared Security + Heterogeneous

Evolution of Polkadot

... is all about flexible usage of cores

You need more to get more out of your core? Async Backing!
You need more cores? Elastic scaling!
You don't want to commit to 6m? Agile-coretime!
You need less than one core? On-demand coretime!
You want to do something other than a parachain in your core? JAM!

Path of a Parachain Block

Note:

In the existing Polkadot, the block itself is put into the DA for further auditing.

Path of a Parachain Block

Notes:

Execution by core validators + made available for further auditing
State root updated by all Polkadot validators

Polkadot's Primitives

In-core execution, with access to DA
On-chain execution, with access to the main Polkadot state

Polkadot's Primitives

Polkadot currently allows you to do a limited thing in-core, and on-chain. What are they?

In-core: Re-execute the PVF, make the PoV accessible to DA
On-chain: Small signature updates

Aside: Blockspace vs. Coretime

In-core, on-chain dualism is unique to execution sharding

Note:
This is why the word blockspace, despite being wildly adopted, is not very sensible in Polkadot, because we have various modes of blockpsace. This is why the word coretime is sometimes used instead of blockspace.

JAM

Now you know everything to understand JAM.

JAM (0)

Gutting of Polkadot such that the following are directly exposed to developers.

What happens In-core
What is placed in Data Availability from the core
What happens On-chain

Note:

A parachain can only control what happens in-core. It cannot really control what happens on-chain. It also cannot readily add any data to the Data availability layer (well, it can, using remarks, which is a hack)

JAM (1)

..and removes a lot of parachain-centric opinions from Polkadot's core protocol.

JAM (2)

..and is therefore intended to be an evolution for the Polkadot Relay Chain.
Parachains, Governance, Staking, AssetHub and everything else remains intact.

Removing Opinions

JAM is programmable via a Service (PVM Bytecode)
Invocation of a service are called a Work Item
- A group of work Items are called Work Package.

Note:

In-core and On-chain

A Service is:
- fn refine(): What happens in-core
- fn accumulate(): What happens on-chain
- fn on_transfer(): Send messages to other services post accumulate
  --

Refine

Massive amounts of gas available (5s PVM)
Access to data availability
- 1.5 PB maximum size / 6s propagation time
Can receive up to 12MB of input data (from DA, or extrinsic data)
No direct access to the JAM state (stateless)
- Except preimages.
Can Invoke child PVMs

Accumulate

Direct access to the JAM state (stateful)
Less gas available (10ms PVM)
Fully synchronous: Access the refine results of all other services, from possibly all other cores at once.

JAM (Recap)

Allowing Services to program exactly how they want to use:

In-core execution
On-chain execution
Data availability

Path of a JAM Work Package

JAM

PVM

Metered (benchmarking 🤢)
Very fast (45% native)
PVM instance can invoke another instance
- Service can invoke a parachain, or smart contract, or anything else
Easy to pause and resume -> Continuation

JAM Misc

JAM offers a similar bulk coretime purchase model to that of Polkadot
- No per-transaction purchase
- Much greater economic freedom for services/applications!

JAM Misc (1)

JAM offers a much more flexible Authorization mechanism for core utilization
- authorize() -> refine() -> accumulate() -> on_transfer()

JAM Envisioned Services

CoreChains
CoreVM / CoreBoot / JAMDocker
CorePlay

`CoreChains`

Entire Polkadot 2 + Parachains is one service

Note: This is an example of JAM's low abstraction level

`CoreVM`

Running normal applications on JAM
Demonstration of PVM's "continuation"
Utilizes DA to store intermediate program state, such as the stack and registers
🎯 DOOM!

`CorePlay`

Ultimate actor based smart contract platform
Non-persistent state partitioning

Note: This is a prime example of JAM's transient decoherence in action

`CorePlay`

JAM Introduction Ends

Questions?

The Web3 Vision and JAM

Abstract look at blockchain/Web3 technology

Blockchain Mental Models

🤮 Database
♾️ State Machine
💻Computer

Blockchain Mental Models

A computer has two main primitives
- ⚙️ Computation
- 💿 Storage

Generic Blockchain Computer

A blockchain/Web3 computer has:
- ⚙️ + 👮‍♂️ Secure computation
  - Canonical ordering + auditability of the said secure computation
- Secure, public-by-default storage
  --

Sequential, Non-Sharded Blockchain Computer

Limited + Expensive computation
Limited + Expensive storage
Fully coherent environment, albeit kinda useless

Sharded Blockchain Computer

Abundant computation
Abundant storage
- Limited + Expensive coherent L1 storage
- Abundant incoherent rollup storage
Fully incoherent environment, which still makes it kinda useless
Multi-core CPU, without any shared memory!

Note:

This model is potentially useful, if you want a lot of throughput, high customization, and don't care much about interoperability

JAM: Supercomputer

Multi-core CPU with shared memory!
JAM is a supercomputer. It is most performant Web3 computer one can build, without sacrificing security

JAM: Supercomputer

Abundant secure computation (ELVES)
Abundant storage
- Limited coherent L1 storage (JAM State)
- Abundant, mostly coherent DA storage ( $D^{3} L$ )
- Fully incoherent service storage

JAM: Web3 Cloud

JAM is like supercomputer that takes the has the most high quality primitives of the Web3 computer, and exposes them all to developers
JAM is the (virtual) Web3 hardware on top of which we can build what we may dare call Web3 Cloud.

Questions

Appendix / Backup Slides

Kernel Update Analogy

Note:

Hardware is what provides compute and bandwidth, and the kernel is part of the OS that moderates the hardware access.
Current Polkadot. A lot of stuff is part of the "Kernel/OS".

Work Item

graph LR 
	subgraph WorkPackage 
		WI1[Work Item 1]
		WI2[Work Item 2]
		WI3[Work Item 3]
	end
	subgraph WorkReport
		WR1[Work Result 1]
		WR2[Work Result 2]
		WR3[Work Result 3]
	end
	
	WI1 --> WR1
	WI2 --> WR2
	WI3 --> WR3

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