Blob Transaction

What is a Blob Transaction?

A blob transaction is a new Ethereum transaction type (Type 3) introduced by EIP-4844 that allows posting large data "blobs" to the network at significantly reduced cost compared to traditional calldata. These blobs are specifically designed for rollup data availability, enabling Layer 2 solutions to publish transaction data to Ethereum more economically.

Each blob can contain up to 128 KB of data and is priced separately from regular execution gas through a dedicated blob gas market. This separation allows blob prices to fluctuate based on blob demand without affecting regular transaction costs.

How it Works

Blob transactions operate through a specialized data handling mechanism:

1. Blob Creation: Rollup sequencer creates blobs containing compressed transaction data
2. KZG Commitment: Each blob is committed using KZG polynomial commitments
3. Transaction Submission: Type 3 transaction includes blob commitments and fees
4. Blob Propagation: Blobs are broadcast separately from the transaction
5. Consensus Verification: Validators verify blob availability during block validation
6. Temporary Storage: Blobs are stored for approximately 18 days
7. Pruning: After the retention period, blob data is pruned from consensus nodes

Key technical features:

• Separate Fee Market: Blob gas has its own base fee with EIP-1559-style dynamics
• Target Capacity: Network targets 3 blobs per block (384 KB)
• Maximum Capacity: Up to 6 blobs per block (768 KB)
• KZG Commitments: Enable efficient data availability sampling in future upgrades

Practical Example

When Base (an Optimism-based rollup) submits a batch of transactions to Ethereum, it creates blob transactions. A typical batch might include 100,000 L2 transactions compressed into 2-3 blobs. The sequencer pays blob gas fees (~0.001-0.01 ETH per blob typically) rather than expensive calldata costs. The blob commitments are included in the Ethereum block, allowing anyone to verify the data was published. For the next 18 days, any node can retrieve the full blob data to verify Base's state or generate fraud proofs.

Why it Matters

Blob transactions represent a paradigm shift in Ethereum's scalability approach:

• ~10x cheaper than calldata for rollup data
• Translates directly to lower L2 fees for users
• Enables more cost-effective high-volume applications

• Foundation for full danksharding
• Supports data availability sampling in future
• Enables continued rollup growth without L1 congestion

• Blob demand doesn't inflate regular gas prices
• Rollups compete in their own fee market
• More predictable costs for L2 operators

Since EIP-4844's activation, Ethereum rollups have seen dramatic fee reductions, making Layer 2 usage more accessible for everyday transactions.