A Smooth Tool for Rollup Understanding the Shared Sorter Astria in One Article

Coin World Network reports:
Author: 1912212.eth, Foresight News
As Ethereum’s Layer 2 networks mature and Gas fees significantly decrease, these networks are experiencing robust growth. However, issues such as suboptimal fees and speeds affecting user experience have emerged. Against this backdrop, the importance of transaction sequencing has become increasingly prominent, serving as a key to resolving transaction bottlenecks and optimizing user experience.
In April this year, Astria, a modular blockchain focused on shared sequencers, completed a $5.5 million seed funding round led by Maven 11, with participation from 1kx, Delphi Ventures, Robot Ventures, and others. Just three months later, Astria secured an additional $12.5 million in funding, led by dba and Placeholder VC, with participation from Hasu, among others.
What is Astria?
Astria is developing a decentralized shared sequencer network aimed at providing Rollups with rapid finality, censorship resistance, composability, and decentralization.
Currently, it is more convenient, cheaper, and user-friendly for L2 to run a centralized sequencer, hence mainstream L2s are managed by their own teams. Although L2 users can submit transactions directly to L1 to bypass the sequencer, they must pay the transaction Gas fee to L1, and the transaction may take longer to finalize.


Sequencers control the order of transactions and, in theory, have the right to exclude user transactions. Sequencers can also extract MEV from transaction sets. If there is only one sequencer, the risk of centralization increases.
Therefore, a decentralized shared sequencer still holds significance.
How Astria Operates
Astria’s decentralized sequencer has multiple sequencer nodes, enabling the sorting of Rollup transactions. In Astria’s operational model, users submit transactions to Rollups, which automatically enter the respective Rollup node’s memory pool. Combiners are responsible for collecting txns and sending them to the sequencer. Finally, the sequencer aggregates the txns into a shared block and sends a pre-confirmation to the user.


Current sequencers are based on specific Rollups. Astria, however, processes blocks in bulk for multiple Rollups. Data compression allows for cost savings when publishing data to L1. The decentralized shared sequencer network incentivizes participants from multiple Rollup ecosystems to act as validators on the network.
Astria Stack
The main components of Astria include five major parts: the combiner, sorting layer, relayer, DA, and scheduler.


Combiner
Technically savvy professionals might directly utilize the sorting layer for better transaction sequencing, but for most ordinary users, this increases complexity. Interacting directly with the sorting layer requires users to hold sequencer tokens and maintain a sequencer wallet, both of which negatively impact user experience.
Astria provides users with a combiner, a tool to abstract this complexity. The combiner acts like a Gas station, bearing the cost of transaction sequencing for users. It also provides users with an unordered guarantee, bundling transactions in the order received.
Sorting Layer
Astria’s sorting layer uses CometBFT as its consensus algorithm. Chains supporting CometBFT can support IBC (Inter-Blockchain Communication), meaning they can cross-chain among many other chains.
The uniqueness of Astria’s sequencer lies in that the transactions it contains are not executed (deferred sorting) but are designated to another execution engine, Rollup. Sequencer nodes can choose to act as ‘validators,’ meaning they actively participate in the production and final determination of new blocks.


Astria’s sequencer application logic allows for three main functions:
Sorting of Rollup data
Value transfer
Changes to the validator set
Relayer
The relayer’s function is to obtain verified blocks from the sequencer and pass them to the DA layer. Since the sequencer’s block time is faster than the DA’s, the relayer first batches ordered data from multiple sequencer blocks, compresses it, and then submits it to the DA.
Individual sequencer blocks can also be acquired by the scheduler before the relayer submits them to the DA. This allows for rapid final confirmation of an improved user experience, acting as a soft commit for the execution layer. The data collection sent by the relayer to the DA layer serves as a source of truth and is ultimately extracted from the DA, serving as a confirmation commit for finality in Rollups.
DA
Astria uses Celestia as the data availability layer, the final destination for all data sorted by the sequencer network. Once data is written to Celestia, the transaction order is considered final, and all data will be extracted from here when new Rollup nodes start.
Scheduler
The scheduler can be considered the consensus implementation of the Rollup full node, similar to the operation node in the OP Stack. The scheduler is the counterpart of the execution engine, together forming a complete Rollup node. Its role is to extract transactions belonging to the Rollup node from each sequencer block and forward them to the execution layer, connecting the sequencer and DA layer to the Rollup execution layer.


For each sequencer block, it extracts the relevant Rollup data required, then validates the batch of Rollup data, and upon validation completion, it converts it into a transaction list and passes it to the execution engine.