@misc{Kruber2009, type = {Master Thesis}, author = {Kruber, Nico}, title = {DHT Load Balancing with Estimated Global Information}, url = {http://nbn-resolving.de/urn:nbn:de:0297-zib-11514}, school = {Zuse Institute Berlin (ZIB)}, year = {2009}, abstract = {One of the biggest impacts on the performance of a Distributed Hash Table (DHT), once established, is its ability to balance load among its nodes. DHTs supporting range queries for example suffer from a potentially huge skew in the distribution of their items since techniques such as consistent hashing can not be applied. Thus explicit load balancing schemes need to be deployed. Several such schemes have been developed and are part of recent research, most of them using only information locally available in order to scale to arbitrary systems. Gossiping techniques however allow the retrieval of fairly good estimates of global information with low overhead. Such information can then be added to existing load balancing algorithms that can use the additional knowledge to improve their performance. Within this thesis several schemes are developed that use global information like the average load and the standard deviation of the load among the nodes to primarily reduce the number of items an algorithm moves to achieve a certain balance. Two novel load balancing algorithms have then been equipped with implementations of those schemes and have been simulated on several scenarios. Most of these variants show better balance results and move far less items than the algorithms they are based on. The best of the developed algorithms achieves a 15-30\% better balance and moves only about 50-70\% of the number of items its underlying algorithm moves. This variation is also very robust to erroneous estimates and scales linearly with the system size and system load. Further experiments with self-tuning algorithms that set an algorithm's parameter according to the system's state show that even more improvements can be gained if additionally applied. Such a variant based on the algorithm described by Karger and Ruhl shows the same balance improvements of 15-30\% as the variant above but reduces the number of item movements further to 40-65\%.}, language = {en} } @misc{MoserHaridiShafaatetal.2009, author = {Moser, Monika and Haridi, Seif and Shafaat, Tallat and Sch{\"u}tt, Thorsten and H{\"o}gqvist, Mikael and Reinefeld, Alexander}, title = {Transactional DHT Algorithms}, issn = {1438-0064}, url = {http://nbn-resolving.de/urn:nbn:de:0297-zib-11532}, number = {09-34}, year = {2009}, abstract = {We present a framework for transactional data access on data stored in a DHT. It allows to atomically read and write items and to run distributed transactions consisting of a sequence of read and write operations on the items. Items are symmetrically replicated in order to achieve durability of data stored in the SON. To provide availability of items despite the unavailability of some replicas, operations on items are quorum-based. They make progress as long as a majority of replicas can be accessed. Our framework processes transactions optimistically with an atomic commit protocol that is based on Paxos atomic commit. We present algorithms for the whole framework with an event based notation. Additionally we discuss the problem of lookup inconsistencies and its implications on the one-copy serializability property of the transaction processing in our framework.}, language = {en} } @misc{Mauter2009, type = {Master Thesis}, author = {Mauter, Daniel}, title = {Ein eingebettetes Hauptspeicher-Datenbanksystem mit Snapshot-Reads}, url = {http://nbn-resolving.de/urn:nbn:de:0297-zib-11552}, school = {Zuse Institute Berlin (ZIB)}, year = {2009}, abstract = {Entwurf und Entwicklung eines eingebetteten Hauptspeicher-Datenbanksystems mit Snapshot-Reads.}, language = {de} } @misc{SchintkeReinefeldHaridietal.2009, author = {Schintke, Florian and Reinefeld, Alexander and Haridi, Seif and Sch{\"u}tt, Thorsten}, title = {Enhanced Paxos Commit for Transactions on DHTs}, issn = {1438-0064}, url = {http://nbn-resolving.de/urn:nbn:de:0297-zib-11448}, number = {09-28}, year = {2009}, abstract = {Key/value stores which are built on structured overlay networks often lack support for atomic transactions and strong data consistency among replicas. This is unfortunate, because consistency guarantees and transactions would allow a wide range of additional application domains to benefit from the inherent scalability and fault-tolerance of DHTs. The Scalaris key/value store supports strong data consistency and atomic transactions. It uses an enhanced Paxos Commit protocol with only four communication steps rather than six. This improvement was possible by exploiting information from the replica distribution in the DHT. Scalaris enables implementation of more reliable and scalable infrastructure for collaborative Web services that require strong consistency and atomic changes across multiple items.}, language = {en} } @misc{Tuschl2009, type = {Master Thesis}, author = {Tuschl, Roland}, title = {Ein Userspace-Dateisystem zur Verwaltung von Grid-Daten}, url = {http://nbn-resolving.de/urn:nbn:de:0297-zib-11483}, school = {Zuse Institute Berlin (ZIB)}, year = {2009}, abstract = {Das Ziel dieser Arbeit ist die Schaffung einer Zugriffs-Komponente f{\"u}r das Grid-Datenmanagement-System ZIB-DMS, das dessen transparente Einbindung in den Verzeichnisbaum eines Linux-Systems erlaubt. Dazu wird unter Verwendung des FUSE-Rahmenwerkes ein Userspace-Dateisystem mit Anbindung an das ZIB-DMS konzipiert und implementiert. Im Fokus stehen dabei die Abbildung der erweiterten Verwaltungsmechanismen des Systems auf die limitierte Schnittstelle hierarchischer Dateisysteme und die dazu notwendigen {\"A}nderungen am ZIB-DMS.}, language = {de} } @misc{Prollius2009, type = {Master Thesis}, author = {Prollius, Christian von}, title = {Ein Peer-to-Peer System mit Bereichsabfragen in PlanetLab}, url = {http://nbn-resolving.de/urn:nbn:de:0297-zib-11492}, school = {Zuse Institute Berlin (ZIB)}, year = {2009}, abstract = {Aktuelle Entwicklungen zeigen, dass Peer-to-Peer (P2P) Anwendungen wie Skype oder Bittorrent im Internet immer mehr an Bedeutung gewinnen. In den letzten Jahren hat es einen explosionsartigen Anstieg an Nutzern und Daten in solchen Netzen gegeben. Dabei stellt der eigentliche Dateitransfer zwischen zwei Rechnern kein großes Problem mehr dar und auch der Speicherbedarf f{\"u}r die große Menge an Daten kann durch die Weiterentwicklung der Hardware gut gedeckt werden. Das eigentliche Problem liegt vielmehr darin, den Rechner zu finden, der die gew{\"u}nschten Daten hat. Client-Server Architekturen, wie zum Beispiel Napster, haben sich als ung{\"u}nstig herausgestellt. Wenige Server, die eine große Anzahl an Clients bedienen m{\"u}ssen, sind einerseits sehr anf{\"a}llig gegen{\"u}ber Angriffen und Ausf{\"a}llen (Single Point of Failure)und kommen auch nicht mit der st{\"a}ndig wachsenden Anzahl an Nutzern zurecht. Verteilte Hashtabellen (DHT) bieten hier einen guten L{\"o}sungsansatz, der mit einer großen Anzahl an Nutzern skaliert und ausfallsicher ist. Andere dezentrale L{\"o}sungen, wie zum Beispiel das P2P Netzwerk Gnutella haben zwar das Problem des Single Point of Failure gel{\"o}st, jedoch haben sie starke Nachteile bei der Suche nach Keys. Bei einer Suche wird ein Broadcast verwendet (jeder schickt die Anfrage an jeden weiter) und damit ein enormer Netzwerkverkehr erzeugt. In "Why Gnutella Can't Scale. No, Really" wird erkl{\"a}rt, dass eine Suchanfrage bei Standardeinstellungen in der Clientsoftware einen Netzwerkverkehr von 17MB erzeugt. Deswegen wird zus{\"a}tzlich eine L{\"o}sung ben{\"o}tigt, die Keys und Values geordnet verteilt, damit sie gezielt gesucht werden k{\"o}nnen. Aus diesem Grund besch{\"a}ftigt sich die folgende Arbeit mit einer v{\"o}llig dezentralen Architektur, die außerdem eine sinnvolle Platzierung der Keys vornimmt. Die dezentrale Architektur hat den Vorteil, dass die Endger{\"a}te den Hauptteil des Dienstes selbst erbringen und damit jeder zus{\"a}tzliche Teilnehmer seine eigenen Ressourcen beisteuert. Diese Arbeit pr{\"a}sentiert Chord\#, eine dezentrale, skalierbare und selbstorganisierende verteilte Hashtabelle. Chord\# wurde ausgew{\"a}hlt, da in dieser Arbeit auch Wert auf Bereichsabfragen gelegt wurde. Diese sind zum Beispiel bei dem Chord Algorithmus nicht m{\"o}glich, da dieser eine Hashfunktion f{\"u}r die Keys verwendet und somit die Daten zwar gleichm{\"a}ßig aber unsortiert auf die Teilnehmer verteilt. Es wird in dieser Arbeit gezeigt, dass mit Hilfe von Chord\# auch ohne die Hashfunktion gute Ergebnisse erzielt werden. Außerdem k{\"o}nnen durch den Verzicht auf die Hashfunktion Bereichsabfragen erm{\"o}glicht werden. Daf{\"u}r wird der Chord\# Algorithmus in Java implementiert (ca. 1500 Zeilen Code) und in dem Forschungsnetz PlanetLab ausf{\"u}hrlich auf Laufzeiten, Instandhaltungskosten und Skalierung getestet.}, language = {de} } @misc{AllalenBrehmStueben2008, author = {Allalen, Mohammed and Brehm, Matthias and St{\"u}ben, Hinnerk}, title = {Performance of Quantum Chromodynamics (QCD) Simulations on the SGI Altix}, issn = {1438-0064}, url = {http://nbn-resolving.de/urn:nbn:de:0297-zib-11086}, number = {08-54}, year = {2008}, abstract = {We study performance and scaling of the Berlin Quantum Chromodynamics Program (BQCD) on the SGI Altix 4700 at Leibniz Supercomputing Centre (LRZ). We employ different communication methods (MPI, MPI with two OpenMP threads per process, as well as the shmem library) and run the MPI version on the two types of nodes of that machine. For comparison with other machines we made performance measurements on an IBM p690 cluster and a Cray XT4.}, language = {en} } @misc{StreuerStueben2008, author = {Streuer, Thomas and St{\"u}ben, Hinnerk}, title = {Simulations of QCD in the Era of Sustained Tflop/s Computing}, issn = {1438-0064}, url = {http://nbn-resolving.de/urn:nbn:de:0297-zib-10623}, number = {07-48}, year = {2008}, abstract = {The latest machine generation installed at supercomputer centres in Germany offers a peak performance in the tens of Tflop/s range. We study performance and scaling of our quantum chromodynamics simulation programme BQCD that we obtained on two of these machines, an IBM Blue Gene/L and an SGI Altix 4700. We compare the performance of Fortran/MPI code with assembler code. The latter allows to exploit concurrency at more levels, in particular in overlapping communication and computation as well as prefetching data from main memory.}, language = {en} } @phdthesis{Roeblitz2009, author = {R{\"o}blitz, Thomas}, title = {Co-Reservation of Resources in the Grid}, isbn = {978-3-86853-137-4}, url = {http://nbn-resolving.de/urn:nbn:de:0297-zib-11626}, year = {2009}, abstract = {Executing applications in the Grid often requires access to multiple geographically distributed resources. In a Grid environment, these resources belong to different administrative domains, each employing its own scheduling policy. That is, at which time an activity (e.g., compute job, data transfer) is started, is decided by the resource's local management system. In such an environment, the coordinated execution of distributed applications requires guarantees on the quality of service (QoS) of the needed resources. Reserving resources in advance is an accepted means to obtain QoS guarantees from a single provider. The challenge, however, is to coordinate advance reservations of multiple resources. This work presents a system architecture and mechanisms to coordinate multiple advance reservations -- called co-reservations -- for delivering QoS guarantees to complex applications. We formally define the co-reservation problem as an optimization problem. The presented model supports three dimensions of freedom: the start time, the duration and the service level of a reservation. Requests and resources are described in a simple language. After matching the static properties and requirements of either side in a mapping, the reservation mechanism probes information about the future status of the resources. The versatile design of the probing step allows the efficient processing of requests, but also lets the resources express their preferences among the myriads of reservation candidates. Next, the best mapping is found through an implementation of the formal co-reservation model. Then, the mapping has to be secured, i.e., resources need to be allocated to a co-reservation candidate with all-or-nothing semantics. We study several goal-driven sequential and concurrent allocation mechanisms and define schemes for handling allocation failures. Finally, we introduce the concept of virtual resources for seamlessly embedding co-reservations into Grid resource management.}, language = {en} } @misc{KolbeckHoegqvistStenderetal.2010, author = {Kolbeck, Bj{\"o}rn and H{\"o}gqvist, Mikael and Stender, Jan and Hupfeld, Felix}, title = {Fault-Tolerant and Decentralized Lease Coordination in Distributed Systems}, issn = {1438-0064}, url = {http://nbn-resolving.de/urn:nbn:de:0297-zib-11658}, number = {10-02}, year = {2010}, abstract = {Applications which need exclusive access to a shared resource in distributed systems require a fault-tolerant and scalable mechanism to coordinate this exclusive access. Examples of such applications include distributed file systems and master/slave data replication. We present Flease, an algorithm for decentralized and fault-tolerant lease coordination in distributed systems. Our algorithm allows the processes competing for a resource to coordinate exclusive access through leases among themselves without a central component. The resulting system easily scales with an increasing number of nodes and resources. We prove that Flease ensures exclusive access, i.e. guarantees that there is at most one valid lease at any time.}, language = {en} }