M.Sc Thesis

M.Sc StudentManuskin Alexander
SubjectOstraka: Blockchain Scaling by Node Sharding
DepartmentDepartment of Electrical and Computer Engineering
Supervisor DR. Ittay Eyal
Full Thesis textFull thesis text - English Version


With their introduction in 2009, cryptocurrencies brought the promise of a global decentralized payment system. However, protocol limitations prevent them from managing the required throughput. Previous work overcame protocol limitations and used low-degree sharding to allow for parallelization. All these systems rely on efficient validation of the transactions, in each shard or globally.

Current blockchain node implementations are limited to running on single machines. In order to increase a nodes’ capacity to process and store transactions, one can only replace its hardware, stifled by advances in Moore’s law. As demand for high throughput systems increases, this becomes a limiting factor, as all participating nodes must process all transactions on the network.

We present Ostraka, an architecture for arbitrary scaling of blockchain nodes that does not affect the security properties of the underlying protocol. Ostraka shards the nodes themselves, embracing the fact major actors have the resources to deploy multi-server nodes. Our novel sharding and communication scheme removes bottlenecks while avoiding exposure to DoS attacks, and may be of independent interest.

We evaluate analytically and experimentally block propagation and processing in various settings. Ostraka achieves linear scaling when the network allows it. Nodes reach a rate of nearly 400 000 transactions per second with 64 shards.