Demystifying

• blog.kianenigma.com/posts/tech/demystifying-jam/presentation-pba

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

Polkadot 1

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

Note:
Sharding and heterogeneity enabled by the use of WASM.

Heterogeneous Execution Sharding, with Shared Security

Let's break it down:

1. Execution Sharding
2. With Shared Security
3. Heterogeneous

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Sequential Blockchain

• Opposite of execution sharding.
• How blockchains usually work

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Poorly Execution Sharded

• Sharding the validator set: less security

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Execution Sharded with Shared Security

• Original vision of ETH 2 was to be this, with 64 shards.
• ELVES

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Heterogeneous

• WASM bytecode

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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

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Path of a Parachain Block

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Path of a Parachain Block

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Path of a Parachain Block

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Path of a Parachain ::: block

Notes:

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

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On-chain vs. In-core

• In-core
  • Executed by a subset of validators + made available for further auditing
• On-chain
  • Executed by all validators: state root update.

In-core, on-chain dualism in execution sharding.

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Data Availability

Polkadot validators already attest to keeping some data available for a long (few weeks) period of time

JAM

Now you know everything to understand JAM.

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JAM (0)

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

1. What happens In-core
2. What happens On-chain
3. What is placed in Data Availability

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)

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JAM (1)

• ..and removes a lot of blockchain/parachain-centric opinions.

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JAM (2)

• ..and is therefore an evolution for the Polkadot Relay Chain (Cloud).
• Parachains, Governance, Staking, AH and everything else remains intact.

Removing Opinions

• JAM is programmable via a Service.
  • PVM Bytecode.
• Invocation of a service are called a Work Item^[1].
  • A group of work Items are called Work Package.

Note:

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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
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Refine

• Massive amounts of gas available.
• Access to data availability (~28 day persistence)
• No direct access to the JAM state (stateless)

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Accumulate

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

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JAM (Recap)

Allowing Services to program exactly how they want to use:

1. In-core execution
2. On-chain execution
3. Data availability

Path of a JAM Work Package

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Path of a JAM Work Package

Path of a JAM Work Package

Path of a JAM Work Package

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Path of a JAM Work Package

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Path of a JAM Work Package

JAM

PVM

• Metered
• Very fast (50% native)
• PVM instance can invoke another instance
• Pause and resume

CoreChains Service

Polkadot Parachains as a JAM Service.

Insights

(personal opinion)

• What is best implemented as a service?
  • Low level
  • Crucial to get this right
• Polkadot has JAM within it, but it is "fixed"
• Services <> Interoperability
• Semi-coherence
• No transactions? Great!

Note:

• Services will likely not be equivalent to smart contract or even parachains; Think more along the lines of "Kernel functions".
  • Crucial to get this right
• Service interoperability? Wrong question.
• Semi-Coherence. Good!
• Polkadot has all the JAM components, but they are fixed.
• Less is more: No transactions? Good!
  come to think of it, a smart contract can have arbitrary, user-defined entry-points. A service is not.

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Questions

Appendix

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".

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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