Investigate on Elastic scaling

[axaysagathiya]

Issue summary (Abstract)

Parity already merged some of the ES code in to the dev branch and probably it was deployed to Kusama and since Gossamer does not support it we need to investigate current state of ES.

Implementation details

• Read articles about elastic scaling
  • https://polkadot.com/blog/rebirth-of-a-network
  • https://wiki.polkadot.network/docs/learn-elastic-scaling
  • https://polkadot.com/blog/elastic-scaling-streamling-growth-on-polkadot
  • https://forum.polkadot.network/t/elastic-scaling/7185/14
• look into the polkadot-sdk elastic scaling issue: Elastic Scaling paritytech/polkadot-sdk#1829

Acceptance criteria (outcomes)

• What modules/subsystems it changes and what modules it adds/removes?
• Is it a must have to implement Elastic Scaling
• When does it become incompatible with previous version? What is the previous version (Async backing)?
• Where it is already merged/deployed? Would it be reverted (we posses information that they might revert it)? @axaysagathiya
• Research Constrain parachain block validity on a specific core polkadot-fellows/RFCs#103

[axaysagathiya]

From what I have observed elastic scaling modifies

• Backing subsystems
  • candidate backing subsystem
  • prospective parachain subsystem
  • statement distribution subsystem
• provisioner subsystem
• collator protocol

[axaysagathiya]

Async backing is the same as elastic scaling with a single core.

In the below images:
P = parachain block
R = relay chain block
C = core
B = backing
I = Inclusion

Elastic scaling with one core

Elastic scaling with two core

[axaysagathiya]

With elastic scaling, parachains can use multiple cores to include multiple parablocks within the same relay chain block

The relay chain receives a sequence of parachain blocks on multiple cores, which are validated and checked if all their state roots line up during their inclusion, but assume they’re unrelated parachain blocks during backing, availability, and approvals.

The elastic scaling implementation will be rolled out in multiple phases.

• In the first phase, elastic scaling is set to work on parachains with a trusted/permissioned collator set. With this restriction, it is possible to launch elastic scaling without changing the candidate receipt.
• After successfully implementing the first phase, changes can be made to the candidate receipt so the collator set can be untrusted/permissionless again.
• The final phase will feature full integration with the Cumulus framework, enabling parachains to be configured to access multiple cores continuously.

These two changes, multiple cores per parachain plus Agile Coretime, come together to enable elastic scaling.

[axaysagathiya]

Learn about agile coretime

• parity article: https://www.parity.io/blog/agilecoretime-explained
• Wiki: https://wiki.polkadot.network/docs/learn-agile-coretime-index

[haikoschol]

This forum post gives an overview of the current status and has a bunch more useful looking links.

[axaysagathiya]

Q: When does it become incompatible with the previous version? What is the previous version (Async backing)?

Backwards compatible. Elastic scaling with 1 core = Async backing.