Introduction 

Within the quickly evolving sphere of blockchain expertise, a big highlight has been solid on Layer 2 scaling options, notably as a response to the urgent scalability challenges inherent in decentralized networks. Amongst these modern options, optimistic rollups have carved out a distinct segment for his or her effectiveness. On the core of those rollups is an integral mechanism often known as the “Sequencer.”

Not too long ago, a novel and transformative idea, dubbed “Shared Sequencing,” has entered the scene, opening up new avenues within the discipline of rollups. This rising concept guarantees to revolutionize the way in which these methods function, probably resulting in substantial enhancements within the effectivity and interoperability of blockchain networks.

A Temporary about Sequencer

Within the framework of optimistic rollups, the sequencer performs a pivotal position. This entity gathers transactions, assembles them into rollup blocks, after which posts these blocks onto the Ethereum essential chain. Moreover, the sequencer is charged with addressing any fraud proofs introduced by members.

This part is crucial within the optimistic rollup construction because it ensures concord between the rollup chain and the Ethereum essential chain. Whereas its capabilities bear a resemblance to these of a proof-of-stake blockchain’s validator, the sequencer possesses a better diploma of authority and affect over the rollup chain.

Immediately ordering transactions on the host chain might be much less economical, an issue the Sequencer adeptly navigates. It accomplishes this by bundling a number of person transactions off-chain, then recording them on the host chain as one collective transaction. This technique not solely cuts down on bills but additionally enhances the efficient use of obtainable sources.

Energy of Sequencer

The Sequencer holds substantial energy in managing the transaction sequence in optimistic rollups. Their position encompasses:

1. Transaction Order Management: The Sequencer performs a pivotal position in figuring out the sequence of transactions inside the rollup. By aggregating a number of person transactions off-chain after which committing them as a single transaction to the principle chain, the Sequencer dictates the order of those transactions. This ordering can considerably influence how transactions are executed and work together inside the rollup.

2. Selective Transaction Inclusion: The Sequencer has the discretion to exclude particular person transactions from the aggregated batch. This exclusion can pressure customers to individually submit their transactions to the principle chain, typically at a better gasoline payment value, granting the Sequencer affect over which transactions are a part of the rollup.

3. Extracting MEV: By means of rearranging the transaction order within the batch earlier than committing to the principle chain, the Sequencer can extract Miner Extractable Worth (MEV). MEV is the potential revenue obtained from transaction order manipulation or front-running by miners or Sequencers. Controlling the transaction sequence permits the Sequencer to probably achieve from sure transaction preparations.

4. Aggregation Obligation: The Sequencer is tasked with amassing a number of off-chain person transactions and mixing them right into a batch for the principle chain. This course of reduces particular person transaction prices for customers by spreading out the general dedication prices.

5. Compression Accountability: Along with aggregation, the Sequencer may compress the transaction set earlier than committing to the principle chain. This compression additional reduces information availability (DA) prices on the host chain, enhancing the rollup’s effectivity by way of storage and processing.

6. Semi-Belief Place: Though the Sequencer has vital management and duties in transaction aggregation and dedication, they’re thought-about a semi-trusted entity. Customers have to belief the Sequencer for honest and environment friendly execution of those duties. The Sequencer can’t block person entry to the rollup however can delay it or impose further prices.

Some Extra Context: Sequencing vs Execution

In optimistic rollups, the ideas of Sequencing and Execution characterize two distinct phases in dealing with transactions:

1. Sequencing: This part includes organizing and grouping transactions off-chain previous to their collective submission to the principle chain. A key participant right here is the Sequencer, who receives particular person transactions from customers and bundles them right into a single transaction set for the host chain. This technique considerably cuts down on prices, because the bills on the principle chain are unfold throughout all transactions within the batch.

Nevertheless, the Sequencer holds the ability to determine the order of transactions, probably excluding some or manipulating the order for extracting most extractable worth (MEV). This locations the Sequencer ready of semi-trust, as they’ll affect the associated fee and precedence of person transactions on the rollup.

It’s essential to grasp that the Sequencer’s job is proscribed to ordering transactions for submission; they don’t compute the state of the rollup.

2. Execution: Contrasting with Sequencing, Execution is about establishing the legit historical past of the rollup and updating its state based mostly on the Sequencer’s ordered transactions. As soon as the Sequencer submits the batch to the principle chain, rollup nodes course of this information, guaranteeing it types a coherent historical past that displays the state adjustments as a consequence of transaction execution.

This course of is deterministic, which means all nodes will attain the identical conclusion from the Sequencer’s ordered set. Subsequently, Proposers finalize this state and commit it to the rollup contract on the host chain, rendering it immutable. This remaining state incorporates the person transactions and is successfully mirrored on the principle chain.

Each Sequencing and Execution are impartial but interlinked processes, important for the scalability and effectivity of optimistic rollups, although they introduce sure compromises by way of belief and management dynamics.

Enter Shared Sequencing

Shared Sequencing in Optimistic Rollups

Shared Sequencing is a way in optimistic rollups the place a number of rollups share a single Sequencer. This Sequencer, a semi-trusted entity, manages the off-chain ordering of transactions and aggregates them, finally committing them as a single batch on the principle blockchain. This technique lowers person prices by distributing the transaction dedication bills over many transactions.

The Sequencer can handle every rollup’s sequence individually or hyperlink a number of rollups’ histories atomically. In atomic linking, the Sequencer ensures that each one transactions from numerous rollups are both collectively confirmed on the principle chain or under no circumstances. This enables for simultaneous transaction execution throughout completely different rollups.

Atomic Inclusion in Multi-Rollup Management

With Shared Sequencing, the Sequencer’s energy extends to sequencing transactions throughout a number of rollups without delay. This results in an idea often known as “atomic inclusion.”

Atomic inclusion permits a shared Sequencer to incorporate a set of transactions throughout a number of rollups concurrently. Customers can specify that these transactions ought to be included in all of the rollups collectively or in none. When using atomic inclusion, the Sequencer commits to sequencing sure transactions throughout numerous rollups concurrently. The target is to make sure that all transactions within the atomic set are included in every rollup’s historical past or excluded from all. This mechanism goals to ensure both full success or whole failure of a set of actions throughout completely different rollups, avoiding incomplete or inconsistent execution.

Atomic inclusion is especially interesting for cross-rollup DeFi composability, because it guarantees extra certainty and reliability for complicated interactions. Nevertheless, it has limitations: solely non-failing or “infallible” transactions might be a part of this course of. Infallible transactions are people who all the time succeed with out producing an invalid state. Consequently, atomic inclusion may not be efficient for transactions susceptible to failure, like sure DeFi swaps or complicated operations.

Whereas atomic inclusion provides vital advantages for particular eventualities, it’s not universally relevant, notably for transactions with larger failure dangers. Reaching true atomic execution throughout rollups might necessitate completely different methods or additional innovation to beat these challenges and guarantee consistency and reliability in cross-rollup operations.

Challenges in Shared Sequencing:

1. Atomic Execution Problem: Making certain atomic execution throughout numerous rollups by means of shared sequencing is complicated. The Sequencer can decide to together with transactions atomically however guaranteeing their atomic execution is problematic, particularly with fallible transactions widespread in DeFi operations, which can fail and disrupt true atomicity.

2. Dependence on Sequencer Trustworthiness: Shared sequencing necessitates belief within the Sequencer’s reliability and honesty. This reliance introduces a central level of belief, as customers rely on the Sequencer to not create conflicting or invalid sequences.

3. Limitations in Cross-Rollup DeFi: Facilitating cross-rollup DeFi transactions by way of shared sequencing is difficult. Advanced DeFi processes typically contain transactions susceptible to failure, which can’t be assured of atomic execution solely by means of inclusion.

4. Advanced Contingency Relationships: Incorporating express contingency hyperlinks between transactions and completely different rollup states can tackle some points however provides complexity for Proposers, who should consider various states based mostly on assumptions about different rollups.

Alternatives in Shared Sequencing:

1. Lowered Prices: By batching and compressing transactions right into a single host chain transaction, shared sequencing can considerably decrease gasoline charges, enhancing the cost-efficiency of rollup transactions.

2. Streamlined Cross-Rollup Transactions: Shared sequencing provides a approach for customers to transact throughout a number of rollups with out direct host chain interplay, streamlining the method by means of a single Sequencer.

3. Simpler Cross-Rollup State Administration: The shared Sequencer can simplify the computation of rollup states by pre-computing and offering execution ensures for transactions throughout completely different rollups.

4. Potential for Future Enhancements: The challenges related to shared sequencing invite additional analysis and improvement, aiming to boost effectivity and safety in cross-rollup interactions.

Conclusion

Shared Sequencing represents a big development in optimistic rollups, enhancing scalability and interoperability amongst numerous rollups. Whereas there are hurdles in reaching seamless atomic execution, its potential in remodeling blockchain expertise is clear. Ongoing analysis and improvement on this space maintain the promise of considerably evolving the blockchain ecosystem, providing new methods for decentralized networks to work together and develop.

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