Dencun¶

Overview¶

Dencun (Deneb-Cancun) is a major Ethereum upgrade activated on March 13, 2024, representing one of the most impactful updates in terms of scalability, security, and transaction efficiency. Deneb refers to the consensus layer upgrade, Cancun refers to the execution layer upgrade, and the two combined are called Dencun.

The most important innovation of this upgrade is the introduction of EIP-4844 (Proto-Danksharding), which significantly reduced transaction fees on Layer 2 networks by introducing temporary data blobs, laying the foundation for Ethereum's Rollup-centric scaling strategy.

Core Feature: EIP-4844¶

Proto-Danksharding¶

EIP-4844, also known as "Proto-Danksharding", is the first step toward full Danksharding:

Blob Transactions

A new transaction type carrying blobs was introduced, extending regular transactions with additional binary large objects (blobs): - Data Size: Each blob stores up to 128 KB of data - Temporary Storage: Blob data is stored on the beacon chain for approximately 18 days (4096 epochs) before being automatically deleted - KZG Commitments: KZG polynomial commitments are used to ensure data integrity - Independent Pricing: Blobs do not occupy block gas space and use an independent fee market

Multi-Dimensional Fee Market

A multi-dimensional fee market was implemented based on EIP-1559: - Blob-carrying transactions do not compete with other transactions for block space - They have an independent blob gas pricing mechanism - Fees are dynamically adjusted based on blob usage - This provides a more predictable L2 cost structure

Data Availability¶

Consensus Layer Access Only

Blob data has a unique design: - Not Accessible by EVM: The execution layer (EVM) cannot directly read blob contents - Only References Visible: The execution layer can only access blob data references (commitments) - Consensus Layer Storage: Blob data is downloaded and stored by beacon nodes (consensus layer) - Limited Retention: Stored for approximately 18 days, long enough for all L2 participants to retrieve the data

Cost Advantage

Due to the temporary storage nature, blob pricing is far lower than permanently stored CALLDATA: - CALLDATA is permanently stored in the historical record - Blobs are pruned after a limited time - This makes blobs the economical choice for L2 data publishing - Prevents permanent storage bloat

Impact on Layer 2¶

Significant Fee Reduction¶

EIP-4844 is designed to reduce gas fees on Ethereum Layer 2 networks by 10-100x:

Actual Results: - Within days of the upgrade, Layer 2 networks such as Arbitrum and Optimism reported fee reductions of up to 90% - Rollups can use blobs instead of expensive CALLDATA to publish data - Users enjoy a low-fee experience close to centralized platforms

Rollup-Centric Strategy¶

The Dencun upgrade successfully established the foundation for Ethereum's Rollup-centric scaling approach: - Mainnet focuses on security and decentralization - Layer 2 provides high throughput and low fees - Blobs serve as the economical data bridge between L2 and mainnet - Proto-Danksharding is a stepping stone toward full Danksharding

Other Important EIPs¶

In addition to EIP-4844, Dencun includes several other improvement proposals:

Consensus Layer (Deneb): - EIP-4788: Beacon block roots available in the EVM - EIP-7044: Perpetual validator exits - EIP-7045: Increase max attestation inclusion slots

Execution Layer (Cancun): - EIP-1153: Transient storage opcodes (TSTORE/TLOAD) - EIP-5656: MCOPY opcode - EIP-6780: Restrict SELFDESTRUCT opcode - EIP-7516: BLOBBASEFEE opcode

Technical Implementation¶

Blob Specifications¶

Capacity Parameters (Initial): - Target blob count: 3 per block - Maximum blob count: 6 per block - Single blob size: 128 KB - Maximum blob data per block: 768 KB (6 x 128 KB)

Pricing Mechanism: - Dynamic pricing based on EIP-1559 - Blob gas price is independent of regular gas - Adjusted based on network blob usage - Provides a predictable cost model

Data Lifecycle¶

Submission: The L2 Sequencer packages batched transaction data into blobs
Publishing: Submitted to Ethereum mainnet via blob-carrying transactions
Availability: Data is stored on the consensus layer for approximately 18 days
Retrieval: L2 nodes and validators can access the data during this period
Pruning: Blob data is automatically deleted after 18 days
Archiving: Third-party archival services can optionally preserve historical blob data

Upgrade Timeline¶

Early 2023: EIP-4844 proposal and specification development
Second half of 2023: Testnet deployment and testing
February 2024: Final testnet validation
March 13, 2024: Mainnet activation

Historical Significance¶

Scaling Milestone

Dencun marks the official beginning of Ethereum's "The Surge" (scaling) era: - First introduction of a dedicated data availability layer on mainnet - Validated the feasibility of blobs and temporary storage - Paved the way for subsequent PeerDAS and full Danksharding

Ecosystem Growth

The fee reduction sparked explosive growth in the L2 ecosystem: - More users migrated to L2 - DeFi, NFT, gaming, and other applications flourished on L2 - Ethereum mainnet positioned itself as the security settlement layer - Rollups became the primary user entry point

Relationship with Subsequent Upgrades¶

Paving the Way for Pectra

The blob mechanism introduced by Dencun laid the foundation for the Pectra upgrade: - Pectra (EIP-7691) increases blob capacity from 3/6 to 6/9 - Further reduces L2 fees - Continues to expand data availability

Toward Fusaka

The PeerDAS in the Fusaka upgrade builds on Dencun's blob foundation: - Optimizes blob data distribution and sampling - Reduces validator storage and bandwidth requirements - Supports larger-scale blob expansion