Rollup’s silky tool? One article to understand the shared sorter Astria

With the increasing maturity of Ethereum's second-layer network and the significant reduction of Gas fees, these networks are showing a trend of vigorous growth, but problems have also emerged, such as fees and speeds that will be affected by many aspects. The impact is unsatisfactory, making the user experience unsatisfactory. In this context, the importance of transaction sequencing has become increasingly prominent, becoming the key to solving transaction bottlenecks and optimizing user experience.

In April this year, Astria, a modular blockchain focusing on shared sequencers, completed a US$5.5 million seed round of financing, led by Maven 11, with participation from 1kx, Delphi Ventures, Robot Ventures, etc. Just 3 months later, Astria completed another $12.5 million in financing, led by dba and Placeholder VC, with participation from Hasu and others.

What is Astria?

Astria is developing a decentralized network of shared orderers designed to provide Rollups with fast finality, censorship resistance, composability, and decentralization.

Currently, it is more convenient, cheaper, and easier for users to use L2 to run a centralized sorter, so mainstream L2 is managed by its own team. While L2 users can submit transactions directly to L1 to bypass the sequencer, users must pay transaction gas fees to L1, and transactions may take longer to finalize.

The sorter controls the ordering of transactions and theoretically has the right not to include user transactions. The sequencer can also extract MEV from the transaction group. If there is only one sorter, the risk of centralization becomes greater.

So a decentralized shared sorter still makes sense.

How Astria works

Astria’s decentralized sorter has multiple sorter nodes to be able to sort Rollup transactions. In Astria's operating mode, users submit transactions to Rollups, and the transactions automatically enter the respective Rollup node memory pools, where the combiner is responsible for collecting txnx and sending it to the sorter. Finally, the sequencer aggregates the txnx into a shared block and finally sends a pre-confirmation to the user.

The current sorters are all implemented based on specific Rollup. Astria processes blocks in batches for multiple Rollups. Data compression provides additional 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 5 parts, namely combiner, sorting layer, relay, DA and scheduler.

Combiner

Technical professionals may be able to directly use the sorting layer to perform better transaction sorting, but it will be more difficult for the vast majority of ordinary users to actually use it. Directly interacting with the sorting layer requires users to hold sorter tokens and maintain sorter wallets, both of which have a significant negative impact on the user experience.

Astria provides users with tools to abstract this complexity through combinators. The combiner is equivalent to a Gas station and bears the sorting cost of user transactions. The combiner also provides users with out-of-order guarantees, bundling transactions in the order they are received.

Ordering Layer

The Astria ordering layer uses CometBFT as its consensus algorithm. A chain that supports CometBFT is able to support IBC (Inter-Blockchain Communication), which means it can cross-chain between many other chains.

The Astria sorter is unique in that the transactions it contains are not executed (lazy sorting) but are instead assigned to another execution engine, Rollup. A sequencer node can choose to act as a "validator," meaning it actively participates in the production and finalization of new blocks.

The application logic of Astria sorter allows three main functions:

• Rollup sorting of data
• Value transfer
• Change of validator set

Relayer

The functions of a repeater are Get the verified chunks from the sequencer and pass them to the DA layer. Since sorters have faster block times than DA, the relay batches the sorted data from multiple sorter blocks before compressing it and submitting it to DA.

Individual sequencer blocks can also be fetched by the scheduler before the relay submits them to the DA. This enables rapid finalization of improved user experience, acting as a soft commit for the execution layer. The collection of data sent by the relay to the DA layer is used as the source of truth and is ultimately extracted from the DA for use as final finality confirmed commits in Rollup.

DA

Astria uses Celestia as the data availability layer and is the final destination for all data sorted by the sorter network. Once data is written to Celestia, the transaction order is considered final and all data will be pulled from here when a new Rollup node is started.

Scheduler

The scheduler can be considered as the consensus implementation of Rollup full node, similar to the operation node in OP Stack. The scheduler is the counterpart of the execution engine, and together they form a complete Rollup node. Its role is to connect the sequencer and DA layer to the Rollup execution layer by extracting transactions belonging to the Rollup node from each sequencer block and forwarding them to the execution layer.

For each sorter block, extract the relevant Rollup data it needs, then validate the batch of Rollup data, wait for the validation to complete, it will convert it into a transaction list and pass it to the execution engine.

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