Tadeusz Kobus

Tadeusz Kobus
Poznan University of Technology · Institute of Computing Science

Doctor of Philosophy

About

16
Publications
316
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64
Citations
Introduction
Tadeusz Kobus is an assistant professor at the Distributed Systems Group in the Institute of Computing Science, Poznań University of Technology, Poland. His current research is focused on various service replication schemes that leverage transactional semantics for concurrency control. His general research interests include distributed computing, transactional memory, replicated systems and group communication systems.

Publications

Publications (16)
Article
In this article we study the properties of distributed systems that mix eventual and strong consistency. We formalize such systems through acute cloud types (ACTs), abstractions similar to conflict-free replicated data types (CRDTs), which by default work in a highly available, eventually consistent fashion, but which also feature strongly consiste...
Preprint
Full-text available
In this paper we introduce Jiffy, the first lock-free, linearizable ordered key-value index that offers both (1) batch updates, which are put and remove operations that are executed atomically, and (2) consistent snapshots used by, e.g., range scan operations. Jiffy is built as a multiversioned lock-free skip list and relies on CPU's Time Stamp Cou...
Conference Paper
In this paper we study the properties of eventually consistent distributed systems that feature arbitrarily complex semantics and mix eventual and strong consistency. These systems execute requests in a highly-available, weakly-consistent fashion, but also enable stronger guarantees through additional inter-replica synchronization mechanisms that r...
Preprint
In this paper we introduce Creek, a low-latency, eventually consistent replication scheme that also enables execution of strongly consistent requests. Creek disseminates the messages among the replicas using only a gossip protocol. Similarly to state machine replication (SMR), Creek totally-orders all requests, but does so using two different mecha...
Preprint
In this paper we study the properties of eventually consistent distributed systems that feature arbitrarily complex semantics and mix eventual and strong consistency. These systems execute requests in a highly-available, weakly-consistent fashion, but also enable stronger guarantees through additional inter-replica synchronization mechanisms that r...
Article
Full-text available
We propose Hybrid Transactional Replication (HTR), a novel replication scheme for highly dependable services. It combines two schemes: a transaction is executed either optimistically by only one service replica in the deferred update mode (DU), or deterministically by all replicas in the state machine mode (SM); the choice is made by an oracle. The...
Article
In this paper we introduce two families of safety properties: -opacity and -linearizability. The new properties relax (to a various degree) the real-time order requirement on transaction execution in opacity and, analogically, the real-time order requirement on operation execution in linearizability. This way we can formalize the guarantees provide...
Article
In the paper, we analyze and experimentally compare two popular replication schemes relying on atomic broadcast: state machine replication (SMR) and deferred update replication (DUR). We estimate the lower bounds on the time of executing requests by the SMR and DUR systems running on multi-core servers. We also consider variants of systems that can...
Conference Paper
Eventually consistent linearizability (ec-linearizability) is a new correctness condition for eventually consistent distributed systems (modeled as shared objects). Unlike the existing definitions of eventual consistency, ec-linearizability is suitable for describing the behaviour of some popular eventually consistent systems, such as Cassandra. It...
Chapter
Transactional replication is a new enabling technology for service replication. Service replication means that a service runs on a group of processes (service replicas) that work together to execute requests issued by external clients. The characteristic feature of transactional replication is that client requests can be processed on a single repli...
Conference Paper
We propose a novel algorithm for hybrid transactional replication (HTR) of highly dependable services. It combines two schemes: a transaction is executed either optimistically by only one service replica in the deferred update mode (DU), or deterministically by all replicas in the state machine mode (SM); the choice is made by an oracle. The DU mod...
Conference Paper
Full-text available
In this paper, we analyze and experimentally compare state-machine-based and deferred-update (or transactional) replication, both relying on atomic broadcast. We define a model that describes the upper and lower bounds on the execution of concurrent requests by a service replicated using either scheme. The model is parametrized by the degree of par...
Conference Paper
Service resilience, defined as the continued availability of a service despite failures and other negative changes in its environment, is vital in many systems. It is typically achieved by state machine replication using group communication middleware for coordination of service replicas. In this paper we focus on systems that represent critical da...

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