The Arbitrum One Sequencer experienced a network outage, sending ripples through the blockchain community. The incident was triggered by an unexpected surge in on-chain activity, primarily driven by inscription transactions. In this article, we delve into the details of this incident, examining the nature of inscription transactions, their impact on the network, and the sequence of events that led to the outage.
I. Inscription Transactions: A Computational Challenge
Inscription transactions, as the name suggests, involve submitting "hex data" on the blockchain. This data typically consists of images and metadata, making inscription transactions more computationally intensive compared to ordinary transactions. These transactions are integral to various blockchains and have been gaining prominence in recent times.
II. A Surge in Inscription Transactions
During the week leading up to the Arbitrum outage, inscription transactions had a significant presence on multiple blockchains, including Polygon, BNB Chain, and Avalanche. According to blockchain analyst Hildobby, inscription transactions accounted for a substantial 57% of the total network traffic across these platforms.
Hildobby's observations revealed that the situation escalated on Arbitrum, where inscription transactions constituted a staggering 90% of all transactions just before the network outage. Moreover, the frequency of hourly inscription transactions on Arbitrum surged significantly in the hours preceding the halt.
III. The Sequence of Events
To better understand the outage, let's examine the chain of events, as summarized by cygaar on Twitter:
Overwhelmed Sequencer: The influx of inscription transactions on Arbitrum overwhelmed the sequencer, hindering the execution of Layer 2 transactions.
Elevated Calldata Batches: Arbitrum transmits compressed transaction data back to the Ethereum Layer 1 (L1). The substantial volume of inscription transactions led to an increased number of calldata batches being sent back to Ethereum L1.
Rising Gas Prices: As more transactions flooded Ethereum L1, gas prices experienced a surge. Elevated gas prices further exacerbated the situation.
Resubmission at Higher Gas Prices: To validate transactions, the Arbitrum sequencer had to resubmit many transactions at higher gas prices, compounding the congestion.
IV. Impact on the Arbitrum Sequencer
As a consequence of these events, the Arbitrum Sequencer's inbox contract witnessed the second-highest gas consumption in the past 24 hours. The outage persisted for approximately 90 minutes before the system was restored, and operations resumed at 12 pm EST.
The Role of Sequencers
Sequencers in an ORU operate analogously to a meticulous clerk. Instead of documenting each transaction as it occurs, they collate numerous off-chain events, creating a summarized version. This summary, termed the "state root," is then uploaded to the primary blockchain, known as L1. By functioning in this manner, sequencers alleviate computational burdens from the main chain.
Sequencers' objectives are transparent: present information accurately. Successful execution of this task results in rewards, establishing a direct correlation between honest behavior and financial incentives. But what happens if a sequencer errs or attempts deceit? This is where the system's ingenious check-and-balance comes into play, introducing the role of verifiers.
Currently, the process of block production on optimistic rollups is commonly overseen by a singular sequencer, often maintained by the originating team. This means ORUs exhibit a centralized nature, although strides are being made to transition to a more decentralized structure. For instance, with "Base," the sequencer is operated singularly by the Base team.
Drawing parallels to block building for Layer 1, the role of the rollup operator is undergoing a transition, becoming more specialized (and centralized) since its initial instantiation. As the economic landscape becomes more expansive, specialization emerges as a natural progression. This results in more resilient systems, thanks to the segregation of duties. However, this expanded specialization also means that the design space has ballooned, necessitating a novel navigational approach.
Balancing Efficiency with Security
Navigating these costs, single rollups encounter critical decisions, balancing security aspirations with efficiency goals. A manifestation of this is the potential inclination towards a less secure, yet more cost-effective data availability layer.
Historically, data publishing costs have been the dominant financial drain. Yet, the horizon seems promising. With the imminent activation of EIP-4844 on Ethereum and the subsequent introduction of full Danksharding, a significant reduction in these costs is anticipated. This will likely empower rollups with the fiscal efficiency requisite for scalability and diversification into novel use cases.
In the grander scheme, the quest for cost efficiency, especially concerning data, seems destined to be fulfilled through offchain innovations. Aggregation emerges as the beacon of hope, promising economies of scale. For instance:
Optimistic rollups could exploit shared sequencing services. An especially intriguing proposition is the potential for shared batch posting. This would expedite batch compression, particularly benefitting smaller entities by providing a blend of reduced costs and enhanced security via accelerated data posting.
Zk rollups have the enticing possibility of shared provers. These provers can conglomerate numerous SNARKs into an overarching proof prior to L1 posting. This model, especially with its recursive aggregation potential, can drastically optimize the L1 data market's utilization. However, this comes at the expense of heightened offchain computation.
V. Future Plans and Transparency
In response to the incident, the Arbitrum team has committed to providing a comprehensive post-mortem analysis. This report will shed light on the precise causes of the outage, the measures taken to address it, and the strategies that will be implemented to prevent similar disruptions in the future.
The recent network outage on the Arbitrum One Sequencer serves as a poignant reminder of the intricacies and challenges that blockchain networks face, particularly when dealing with computationally intensive transactions like inscriptions. As the blockchain ecosystem continues to evolve, maintaining the stability and resilience of these networks remains a paramount concern. It is through such incidents and the subsequent learnings that the blockchain community can strive for greater reliability and transparency in the face of growing demand and complexity.
