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<title>RFC-0139: Faster Erasure Coding - Polkadot Fellowship RFCs</title>
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<ol class="chapter"><li class="chapter-item expanded affix "><a href="../introduction.html">Introduction</a></li><li class="spacer"></li><li class="chapter-item expanded affix "><li class="part-title">Newly Proposed</li><li class="spacer"></li><li class="chapter-item expanded affix "><li class="part-title">Proposed</li><li class="chapter-item expanded "><a href="../proposed/0150-voting-while-delegating.html">RFC-150: Allow Voting While Delegating</a></li><li class="chapter-item expanded "><a href="../proposed/0154-multi-slot-aura.html">RFC-0154: AURA Multi-Slot Collation </a></li><li class="chapter-item expanded "><a href="../proposed/0155-pUSD.html">RFC-0155: pUSD (Polkadot USD over-collateralised debt token)</a></li><li class="chapter-item expanded "><a href="../proposed/0156-bls-signatures.html">RFC-0156: Add BLS12-381 Host Functions</a></li><li class="spacer"></li><li class="chapter-item expanded affix "><li class="part-title">Approved</li><li class="chapter-item expanded "><a href="../approved/0001-agile-coretime.html">RFC-1: Agile Coretime</a></li><li class="chapter-item expanded "><a href="../approved/0005-coretime-interface.html">RFC-5: Coretime Interface</a></li><li class="chapter-item expanded "><a href="../approved/0007-system-collator-selection.html">RFC-0007: System Collator Selection</a></li><li class="chapter-item expanded "><a href="../approved/0008-parachain-bootnodes-dht.html">RFC-0008: Store parachain bootnodes in relay chain DHT</a></li><li class="chapter-item expanded "><a href="../approved/0009-improved-net-light-client-requests.html">RFC-0009: Improved light client requests networking protocol</a></li><li class="chapter-item expanded "><a href="../approved/0010-burn-coretime-revenue.html">RFC-0010: Burn Coretime Revenue</a></li><li class="chapter-item expanded "><a href="../approved/0012-process-for-adding-new-collectives.html">RFC-0012: Process for Adding New System Collectives</a></li><li class="chapter-item expanded "><a href="../approved/0013-prepare-blockbuilder-and-core-runtime-apis-for-mbms.html">RFC-0013: Prepare Core runtime API for MBMs</a></li><li class="chapter-item expanded "><a href="../approved/0014-improve-locking-mechanism-for-parachains.html">RFC-0014: Improve locking mechanism for parachains</a></li><li class="chapter-item expanded "><a href="../approved/0017-coretime-market-redesign.html">RFC-0017: Coretime Market Redesign</a></li><li class="chapter-item expanded "><a href="../approved/0022-adopt-encointer-runtime.html">RFC-0022: Adopt Encointer Runtime</a></li><li class="chapter-item expanded "><a href="../approved/0026-sassafras-consensus.html">RFC-0026: Sassafras Consensus Protocol</a></li><li class="chapter-item expanded "><a href="../approved/0032-minimal-relay.html">RFC-0032: Minimal Relay</a></li><li class="chapter-item expanded "><a href="../approved/0042-extrinsics-state-version.html">RFC-0042: Add System version that replaces StateVersion on RuntimeVersion</a></li><li class="chapter-item expanded "><a href="../approved/0043-storage-proof-size-hostfunction.html">RFC-0043: Introduce storage_proof_size Host Function for Improved Parachain Block Utilization</a></li><li class="chapter-item expanded "><a href="../approved/0045-nft-deposits-asset-hub.html">RFC-0045: Lowering NFT Deposits on Asset Hub</a></li><li class="chapter-item expanded "><a href="../approved/0047-assignment-of-availability-chunks.html">RFC-0047: Assignment of availability chunks to validators</a></li><li class="chapter-item expanded "><a href="../approved/0048-session-keys-runtime-api.html">RFC-0048: Generate ownership proof for SessionKeys</a></li><li class="chapter-item expanded "><a href="../approved/0050-fellowship-salaries.html">RFC-0050: Fellowship Salaries</a></li><li class="chapter-item expanded "><a href="../approved/0056-one-transaction-per-notification.html">RFC-0056: Enforce only one transaction per notification</a></li><li class="chapter-item expanded "><a href="../approved/0059-nodes-capabilities-discovery.html">RFC-0059: Add a discovery mechanism for nodes based on their capabilities</a></li><li class="chapter-item expanded "><a href="../approved/0078-merkleized-metadata.html">RFC-0078: Merkleized Metadata</a></li><li class="chapter-item expanded "><a href="../approved/0084-general-transaction-extrinsic-format.html">RFC-0084: General transactions in extrinsic format</a></li><li class="chapter-item expanded "><a href="../approved/0091-dht-record-creation-time.html">RFC-0091: DHT Authority discovery record creation time</a></li><li class="chapter-item expanded "><a href="../approved/0097-unbonding_queue.html">RFC-0097: Unbonding Queue</a></li><li class="chapter-item expanded "><a href="../approved/0099-transaction-extension-version.html">RFC-0099: Introduce a transaction extension version</a></li><li class="chapter-item expanded "><a href="../approved/0100-xcm-multi-type-asset-transfer.html">RFC-0100: New XCM instruction: InitiateAssetsTransfer</a></li><li class="chapter-item expanded "><a href="../approved/0101-xcm-transact-remove-max-weight-param.html">RFC-0101: XCM Transact remove require_weight_at_most parameter</a></li><li class="chapter-item expanded "><a href="../approved/0103-introduce-core-index-commitment.html">RFC-0103: Introduce a CoreIndex commitment and a SessionIndex field in candidate receipts</a></li><li class="chapter-item expanded "><a href="../approved/0105-xcm-improved-fee-mechanism.html">RFC-0105: XCM improved fee mechanism</a></li><li class="chapter-item expanded "><a href="../approved/0107-xcm-execution-hints.html">RFC-0107: XCM Execution hints</a></li><li class="chapter-item expanded "><a href="../approved/0108-xcm-remove-testnet-ids.html">RFC-0108: Remove XCM testnet NetworkIds</a></li><li class="chapter-item expanded "><a href="../approved/0122-alias-origin-on-asset-transfers.html">RFC-0122: Asset transfers can alias XCM origin on destination to original origin</a></li><li class="chapter-item expanded "><a href="../approved/0123-pending-code-as-storage-location-for-runtime-upgrades.html">RFC-0123: Introduce :pending_code as intermediate storage key for the runtime code</a></li><li class="chapter-item expanded "><a href="../approved/0125-xcm-asset-metadata.html">RFC-0125: XCM Asset Metadata</a></li><li class="chapter-item expanded "><a href="../approved/0126-introduce-pvq.html">RFC-0126: Introduce PVQ (PolkaVM Query)</a></li><li class="chapter-item expanded "><a href="../approved/0135-compressed-blob-prefixes.html">RFC-0135: Compressed Blob Prefixes</a></li><li class="chapter-item expanded "><a href="../approved/0139-faster-erasure-coding.html" class="active">RFC-0139: Faster Erasure Coding</a></li><li class="chapter-item expanded "><a href="../approved/0146-deflationary-fee-proposal.html">RFC-0146: Deflationary Transaction Fee Model for the Relay Chain and its System Parachains</a></li><li class="chapter-item expanded "><a href="../approved/0149-rfc-1-renewal-adjustment.html">RFC-0149: Renewal Adjustment</a></li><li class="spacer"></li><li class="chapter-item expanded affix "><li class="part-title">Stale</li><li class="chapter-item expanded "><a href="../stale/0000-pre-elves_soft.html">RFC-0000: Pre-ELVES soft concensus</a></li><li class="chapter-item expanded "><a href="../stale/0000-rewards.html">RFC-0000: Validator Rewards</a></li><li class="chapter-item expanded "><a href="../stale/0004-remove-unnecessary-allocator-usage.html">RFC-0004: Remove the host-side runtime memory allocator</a></li><li class="chapter-item expanded "><a href="../stale/0006-dynamic-pricing-for-bulk-coretime-sales.html">RFC-0006: Dynamic Pricing for Bulk Coretime Sales</a></li><li class="chapter-item expanded "><a href="../stale/0034-xcm-absolute-location-account-derivation.html">RFC-34: XCM Absolute Location Account Derivation</a></li><li class="chapter-item expanded "><a href="../stale/0035-conviction-voting-delegation-modifications.html"> RFC-0035: Conviction Voting Delegation Modifications</a></li><li class="chapter-item expanded "><a href="../stale/0044-rent-based-registration.html">RFC-0044: Rent based registration model</a></li><li class="chapter-item expanded "><a href="../stale/0054-remove-heap-pages.html">RFC-0054: Remove the concept of "heap pages" from the client</a></li><li class="chapter-item expanded "><a href="../stale/0070-x-track-kusamanetwork.html">RFC-0070: X Track for @kusamanetwork</a></li><li class="chapter-item expanded "><a href="../stale/0073-referedum-deposit-track.html">RFC-0073: Decision Deposit Referendum Track</a></li><li class="chapter-item expanded "><a href="../stale/0074-stateful-multisig-pallet.html">RFC-0074: Stateful Multisig Pallet</a></li><li class="chapter-item expanded "><a href="../stale/0077-increase-max-length-of-identity-pgp-fingerprint-value.html">RFC-0077: Increase maximum length of identity PGP fingerprint values from 20 bytes</a></li><li class="chapter-item expanded "><a href="../stale/0088-broker-pallet-slashable-deposit-purchaser-reputation-reserved-cores.html">RFC-0088: Add slashable locked deposit, purchaser reputation, and reserved cores for on-chain identities to broker pallet</a></li><li class="chapter-item expanded "><a href="../stale/00xx-secondary-marketplace-for-regions.html">RFC-0001: Secondary Market for Regions</a></li><li class="chapter-item expanded "><a href="../stale/00xx-smart-contracts-coretime-chain.html">RFC-0002: Smart Contracts on the Coretime Chain</a></li><li class="chapter-item expanded "><a href="../stale/0102-offchain-parachain-runtime-upgrades.html">RFC-0000: Feature Name Here</a></li><li class="chapter-item expanded "><a href="../stale/0106-xcm-remove-fees-mode.html">RFC-0106: Remove XCM fees mode</a></li><li class="chapter-item expanded "><a href="../stale/0111-pure-proxy-replication.html">RFC-0111: Pure Proxy Replication</a></li><li class="chapter-item expanded "><a href="../stale/0112-compress-state-response-message-in-state-sync.html">RFC-0112: Compress the State Response Message in State Sync</a></li><li class="chapter-item expanded "><a href="../stale/0114-secp256r1-hostfunction.html">RFC-0114: Introduce secp256r1_ecdsa_verify_prehashed Host Function to verify NIST-P256 elliptic curve signatures</a></li><li class="chapter-item expanded "><a href="../stale/0117-unbrick-collective.html">RFC-0117: The Unbrick Collective</a></li><li class="chapter-item expanded "><a href="../stale/0120-referenda-confirmation-by-candle-mechanism.html">RFC-0120: Referenda Confirmation by Candle Mechanism</a></li><li class="chapter-item expanded "><a href="../stale/0124-extrinsic-version-5.html">RFC-0124: Extrinsic version 5</a></li><li class="chapter-item expanded "><a href="../stale/0138-invulnerable-collator-election.html">RFC-0138: Election mechanism for invulnerable collators on system chains</a></li><li class="chapter-item expanded "><a href="../stale/0152-decentralized-convex-preference-coretime-market-for-polkadot.html">RFC-0152: Decentralized Convex-Preference Coretime Market for Polkadot</a></li><li class="chapter-item expanded "><a href="../stale/RFC-114 Adjust Tipper Track Confirmation Periods.html">RFC-114: Adjust Tipper Track Confirmation Periods</a></li><li class="chapter-item expanded "><a href="../stale/TODO-stale-nomination-reward-curve.html">RFC-TODO: Stale Nomination Reward Curve</a></li><li class="chapter-item expanded "><a href="../stale/xxxx-improve-the-security-of-proof-of-possession.html">RFC-XXXX: Adding customized mandatory context to proof of possession statement</a></li></ol>
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<p><a href="https://github.com/polkadot-fellows/RFCs/blob/main/text/0139-faster-erasure-coding.md">(source)</a></p>
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<p><strong>Table of Contents</strong></p>
|
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<ul>
|
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<li><a href="#rfc-0139-faster-erasure-coding">RFC-0139: Faster Erasure Coding</a>
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<ul>
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<li><a href="#summary">Summary</a></li>
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<li><a href="#motivation">Motivation</a></li>
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<li><a href="#stakeholders">Stakeholders</a></li>
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<li><a href="#explanation">Explanation</a>
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<ul>
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<li><a href="#upgrade-path">Upgrade path</a></li>
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</ul>
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</li>
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<li><a href="#drawbacks">Drawbacks</a></li>
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<li><a href="#testing-security-and-privacy">Testing, Security, and Privacy</a></li>
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<li><a href="#performance-and-compatibility">Performance and Compatibility</a>
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<ul>
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<li><a href="#performance">Performance</a></li>
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<li><a href="#compatibility">Compatibility</a></li>
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</ul>
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</li>
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<li><a href="#prior-art-and-references">Prior Art and References</a></li>
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<li><a href="#unresolved-questions">Unresolved Questions</a></li>
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<li><a href="#future-directions-and-related-material">Future Directions and Related Material</a></li>
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</ul>
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</li>
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</ul>
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<h1 id="rfc-0139-faster-erasure-coding"><a class="header" href="#rfc-0139-faster-erasure-coding">RFC-0139: Faster Erasure Coding</a></h1>
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<div class="table-wrapper"><table><thead><tr><th></th><th></th></tr></thead><tbody>
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<tr><td><strong>Start Date</strong></td><td>7 March 2025</td></tr>
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<tr><td><strong>Description</strong></td><td>Faster algorithm for Data Availability Layer</td></tr>
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<tr><td><strong>Authors</strong></td><td>ordian</td></tr>
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</tbody></table>
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</div>
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<h2 id="summary"><a class="header" href="#summary">Summary</a></h2>
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<p>This RFC proposes changes to the erasure coding algorithm and the method for computing the erasure root on Polkadot to improve performance of both processes.</p>
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<h2 id="motivation"><a class="header" href="#motivation">Motivation</a></h2>
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<p>The Data Availability (DA) Layer in Polkadot provides a foundation for
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shared security, enabling Approval Checkers and Collators to download
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Proofs-of-Validity (PoV) for security and liveness purposes respectively.
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As the number of parachains and PoV sizes increase, optimizing the performance
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of the DA layer becomes increasingly critical.</p>
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<p><a href="https://github.com/polkadot-fellows/RFCs/blob/main/text/0047-assignment-of-availability-chunks.md">RFC-47</a>
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proposed enabling systematic chunk recovery for Polkadot's DA to improve
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efficiency and reduce CPU overhead. However, while it helps under the assumption of
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good network connectivity to a specific one-third of validators (modulo some
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backup tolerance on backers), it still requires re-encoding. Therefore,
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we need to ensure the system can handle load in the worst-case scenario.
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The proposed change is orthogonal to RFC-47 and can be used in conjunction with it.</p>
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<p>Since RFC-47 already requires a breaking protocol change (including changes to
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collator nodes), we propose bundling another performance-enhancing breaking
|
||
change that addresses the CPU bottleneck in the erasure coding process, but using
|
||
a separate node feature (<code>NodeFeatures</code> part of <code>HostConfiguration</code>) for its activation.</p>
|
||
<h2 id="stakeholders"><a class="header" href="#stakeholders">Stakeholders</a></h2>
|
||
<ul>
|
||
<li>Infrastructure providers (operators of validator/collator nodes)
|
||
will need to upgrade their client version in a timely manner</li>
|
||
</ul>
|
||
<h2 id="explanation"><a class="header" href="#explanation">Explanation</a></h2>
|
||
<p>We propose two specific changes:</p>
|
||
<ol>
|
||
<li>
|
||
<p>Switch to the erasure coding algorithm described in the Graypaper,
|
||
Appendix H. SIMD implementations of this algorithm are available in:</p>
|
||
<ul>
|
||
<li><a href="https://github.com/AndersTrier/reed-solomon-simd">Rust</a></li>
|
||
<li><a href="https://github.com/catid/leopard">C++</a></li>
|
||
<li><a href="https://github.com/celestiaorg/go-leopard">Go</a></li>
|
||
</ul>
|
||
</li>
|
||
<li>
|
||
<p>Replace the Merkle Patricia Trie with a Binary Merkle Tree for computing the erasure root.</p>
|
||
</li>
|
||
</ol>
|
||
<p>The reference root merklization implementation can be found <a href="https://github.com/paritytech/erasure-coding/blob/512e77472beb877fe0881a857623d54d97b82bc4/src/merklize.rs#L9-L197">here</a>.</p>
|
||
<h3 id="upgrade-path"><a class="header" href="#upgrade-path">Upgrade path</a></h3>
|
||
<p>We propose adding support for the new erasure coding scheme on both validator and collator sides without activating it until:</p>
|
||
<ol>
|
||
<li>All validators have upgraded</li>
|
||
<li>Most collators have upgraded</li>
|
||
</ol>
|
||
<p>Block-authoring collators that remain on the old version will be unable to produce valid candidates until they upgrade. Parachain full nodes will continue to function normally without changes.</p>
|
||
<p>An alternative approach would be to allow collators to opt-in to the new erasure
|
||
coding scheme using a reserved field in the candidate receipt. This would allow
|
||
faster deployment for most parachains but would add complexity.</p>
|
||
<p>Given there isn't urgent demand for supporting larger PoVs currently, we recommend prioritizing simplicity with a way to implement future-proofing changes.</p>
|
||
<p>In short, the following steps are proposed:</p>
|
||
<ol>
|
||
<li>Implement the changes a and wait for most collators to upgrade.</li>
|
||
<li>Activate RFC-47 via <code>Configuration::set_node_feature</code> runtime change.</li>
|
||
<li>Activate the new erasure coding scheme using another <code>Configuration::set_node_feature</code> runtime change.</li>
|
||
</ol>
|
||
<h2 id="drawbacks"><a class="header" href="#drawbacks">Drawbacks</a></h2>
|
||
<p>Bundling this breaking change with RFC-47 might reset progress in updating collators. However, the omni node initiative should help mitigate this issue.</p>
|
||
<h2 id="testing-security-and-privacy"><a class="header" href="#testing-security-and-privacy">Testing, Security, and Privacy</a></h2>
|
||
<p>Testing is needed to ensure binary compatibility across implementations in multiple languages.</p>
|
||
<h2 id="performance-and-compatibility"><a class="header" href="#performance-and-compatibility">Performance and Compatibility</a></h2>
|
||
<h3 id="performance"><a class="header" href="#performance">Performance</a></h3>
|
||
<p>According to <a href="https://gist.github.com/ordian/0af2822e20bf905d53410a48dc122fd0">benchmarks</a>:</p>
|
||
<ul>
|
||
<li>A proper SIMD implementation of Reed-Solomon is 3-4× faster for encoding and up to 9× faster for full decoding</li>
|
||
<li>Binary Merkle Trees produce proofs that are 4× smaller and slightly faster to generate and verify</li>
|
||
</ul>
|
||
<h3 id="compatibility"><a class="header" href="#compatibility">Compatibility</a></h3>
|
||
<p>This requires a breaking change that can be coordinated following the same approach as in RFC-47.</p>
|
||
<h2 id="prior-art-and-references"><a class="header" href="#prior-art-and-references">Prior Art and References</a></h2>
|
||
<p>JAM already utilizes the same optimizations described in the Graypaper.</p>
|
||
<h2 id="unresolved-questions"><a class="header" href="#unresolved-questions">Unresolved Questions</a></h2>
|
||
<p>None.</p>
|
||
<h2 id="future-directions-and-related-material"><a class="header" href="#future-directions-and-related-material">Future Directions and Related Material</a></h2>
|
||
<p>Future improvements could include:</p>
|
||
<ul>
|
||
<li>Using ZK proofs to eliminate the need for re-encoding data to verify correct encoding</li>
|
||
<li>Removing the requirement for collators to compute the erasure root for the collator protocol</li>
|
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