Daniel Schall

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Because energy use of single-server systems is far from being <i>energy proportional</i>, we explore whether or not better energy efficiency may be achieved by a cluster of nodes whose size is dynamically adjusted to the current workload demand. As data-intensive workloads, we submit specific TPC-H queries against a distributed shared-nothing DBMS, where(More)
Due to the energy consumption/resource utilization characteristics of todays centralized DB servers, the fastest configuration is also the most energy-efficient one. Extensive use of SSDs alone cannot enable a fundamental change of this overall picture, because the storagerelated energy consumption is typically only a little fraction of the overall energy(More)
Presently, solid state disks (SSDs) are emerging as a disruptive storage technology and promise breakthroughs for important application properties. They quickly enter the enterprise domain and (partially) replace magnetic disks (HDDs) for database servers. To identify performance and energy use of both types of storage devices, we have built an analysis(More)
The sensitivity of graphene based devices to surface adsorbates and charge traps at the graphene/dielectric interface requires proper device passivation in order to operate them reproducibly under ambient conditions. Here we report on the use of atomic layer deposited aluminum oxide as passivation layer on graphene field effect devices (GFETs). We show that(More)
The growing energy consumption of data centers has become an area of research interest lately. For this reason, the research focus has broadened from a solely performance-oriented system evaluation to an exploration where energy efficiency is considered as well. The Transaction Processing Performance Council (TPC) has also reflected this shift by(More)
Traditional database management systems (DBMSs) running on powerful single-node servers are usually over-provisioned for most of their daily workloads and, because they do not show good-enough energy proportionality, waste a lot of energy while underutilized. A cluster of small (wimpy) servers, where its size can be dynamically adjusted to the current(More)
Previous DB research clearly concluded that the most energy-efficient configuration of a single-server DBMS is typically the highest performing one. This observation is certainly true if we focus in isolation on specific applications where the DBMS can steadily run in the peak-performance range. Because we noticed that typical DBMS activity levels—or its(More)
With flash disks being an important alternative to conventional magnetic disks, various design aspects of DBMSs, whose I/O behavior is performance-critical, and especially their I/O architecture should be reconsidered. Taking the distinguished characteristics of flash disks into account, several flash-aware buffer algorithms have been proposed with focus on(More)
Graphene is considered a promising material for broadband opto-electronics because of its linear and gapless band structure. Its optical conductivity can be significantly tuned electrostatically by shifting the Fermi level. Using mentioned property, we experimentally demonstrate a graphene based electro-absorption modulator with very low insertion loss. The(More)