In recent years, multi-tier architectures have become the standard computing environment for web- and enterprise applications. The application server tier is often the heart of the system embedding the business logic. Adaptability, in particular the capability to adjust to the load submitted to the system and to handle the failure of individual components, are of outmost importance in order to provide 7/24 access and high performance. Replication is a common means to achieve these reliability and scalability requirements. With replication, the application server tier consists of several server replicas. Thus, if one replica fails, others can take over. Furthermore, the load can be distributed across the available replicas. Although many replication solutions have been proposed so far, most of them have been either developed for fault-tolerance or for scalability. Furthermore, only few have considered that the application server tier is only one tier in a multi-tier architecture, that this tier maintains state, and that execution in this environment can follow complex patterns. Thus, existing solutions often do not provide correctness beyond some basic application scenarios. / In this thesis we tackle the issue of replication of the application server tier from ground off and develop a unified solution that provides both fault-tolerance and scalability. We first describe a set of execution patterns that describe how requests are typically executed in multi-tier architectures. They consider the flow of execution across client tier, application server tier, and database tier. In particular, the execution patterns describe how requests are associated with transactions, the fundamental execution units at application server and database tiers. Having these execution patterns in mind, we provide a formal definition of what it means to provide a correct execution across all tiers, even in case failures occur and the application server tier is replicated. Informally, a replicated system is correct if it behaves exactly as a non-replicated that never fails. From there, we propose a set of replication algorithms for fault-tolerance that provide correctness for the execution patterns that we have identified The main principle is to let a primary AS replica to execute all client requests, and to propagate any state changes performed by a transaction to backup replicas at transaction commit time. The challenges occur as requests can be associated in different ways with transactions. Then, we extend our fault-tolerance solution and develop a unified solution that provides both fault-tolerance and load-balancing. In this extended solution, each application server replica is able to execute client requests as a primary and at the same time serves as backup for other replicas. The framework provides a transparent, truly distributed and lightweight load distribution mechanism which takes advantage of the fault-tolerance infrastructure. Our replication tool is implemented as a plug-in of JBoss application server and the performance is carefully evaluated, comparing with JBoss' own replication solutions. The evaluation shows that our protocols have very good performance and compare favorably with existing solutions.

Magistro baigiamajame darbe išanalizuota nuolatinės buveinės samprata fizinėje erdvėje ir ją nustatantys kriterijai, bei atskleistas minėtų kriterijų turinys. Vadovaujantis nustatytais kriterijais išanalizuota nuolatinės buveinės samprata elektroninėje komercijoje ir pateiktos priemonės, kuriomis remiantis nustatoma nuolatinė buveinė elektroninėje komercijoje, nurodytos galimos problemos ir esami problemų sprendimo būdai, bei identifikuotos, kai kurios naujos problemos, kurios reikalauja tolimesnio tyrimo. Pirmojoje darbo dalyje aptarta nuolatinės buveinės samprata fizinėje erdvėje ir išskirti pagrindiniai kriterijai, turintys įtakos nustatant nuolatinės buveinės buvimo faktą fizinėje erdvėje. Antroje dalyje atsižvelgiant į nustatytus kriterijus išanalizuota nuolatinė buveinė elektroninėje komercijoje ir nustatyti skirtumai ir panašumai su nuolatine buveine fizinėje erdvėje. Trečioje darbo dalyje ištirta užsienio valstybių ir Lietuvos praktika nuolatinės buveinės kontekste. / This master‘s degree thesis is about permanent establishment in physical space and it’s parameters. These parameters and definition of permanent establishment are analyzed in details. In accordance with the criteria laid down in the analysis, conception of permanent establishment in e-commerce was reviewed and remedies for identification of permanent establishment were proposed for e-commerce. Also in this thesis major problems related to permanent establishment and their existing resolutions are considered, including new problems identified that should be analyzed collaterally. In the first chapter of this thesis conception of permanent establishment in physical space is analyzed and main criteria that have direct or indirect impact to identification of permanent establishment in physical space are excluded. The second chapter is dedicated for analysis of permanent establishment in e-commerce and identification of principal discrepancies and similarities, while comparing it with physical space. In the third chapter of this thesis survey of Lithuania’s and other foreign countries’ practices related to permanent establishment is presented.

Duomenų sinchronizacija yra neatsiejama šiomis dienomis, kuomet eina kalba apie paskirstytas aplikacijas, kurios veikia mobiliuose įrenginiuose. Kuomet duomenys yra sinchronizuojami mobiliajame įrenginyje, jų vartotojai yra nepriklausomi nuo duomenų serverio ir gali laisvai naudotis lokaliais duomenis atsijungę nuo tinklo. [14] Šiame darbe išnagrinėjome galimas duomenų prieigos architektūras: 1. Visuomet atsijungęs 2. Visuomet prisijungęs 3. Mišrus Taip pat aptarėme techninės realizacijos ypatumus, problemas su kuriomis susiduriama, kuriant sinchronizacijos algoritmus bei būtiną informaciją reikalingą šių algoritmų funkcionavimui (ID valdymas, pakeitimų sekimas, greita/lėta sinchronizacija ir kt.). Projektinėje dalyje buvo išnagrinėtos jau egzistuojančios sistemos architektūra, bei aprašyti reikalingi pakeitimai, tam kad būtų galima įtraukti sinchronizacijos procesą į sistemos funkcionalumą. Galiausiai detaliai išanalizavome mišrios duomenų prieigos architektūrą, jos paskirtį, privalumus ir trūkumus. Taip pat sudarėme imitacinį modelį pagal šios architektūros principus panaudodami sudėtingų sistemų formalizavimo agregatinį metodą bei atlikome jo parametrų analizę. / Distributed applications are modeled around replicating copies of the same data on many hosts in a network for a variety of reasons. For one, system designers can alleviate the single-server implosion problem and instead distribute client requests for data across many hosting servers. Second, making data locally available on a host speeds up applications because the applications do not block for network input/output as data is transmitted. In this work we have analyzed several data access architectures: 1. Always offline 2. Always online 3. Mixed architecture Also we have described technical implementation details, problems which occur developing synchronization algorithms and mandatory information which is needed for these algorithms to work correctly (ID handling, change detection, fast/slow synchronization etc.). Furthermore, we investigated existing system architecture and defined mandatory changes needed for incorporating synchronization process into system functionality. Finally, we did detail analysis of mixed data access architecture, which included real world appliance, pros and cons. After that we created a model using complex systems formalization aggregation method which was based on these architecture principles. Also we did models parameter analysis in experimental part.

Magistro darbe apžvelgiamos virtualizavimo programos. Nustatomi jų trūkumai ir privalumai kuriant virtualizavimo infrastruktūra įmonės IT skyriui. Parenkamas tinkamiausias virtualizavimo būdas IT skyriui. / Due to the flexibility of virtualization there is a good chance that there is a virtual design or system to meet the most demanding needs and because of this virtualization is merely duplicating the revolution in open systems by supplying a wide variety of solutions and meet any IT needs.

Ne tik administratoriai, bet ir vartotojai vis daugiau dirba nuotoliniu būdu, prisijungę prie serverių. Būtina užtikrinti saugų prisijungimą prie tokių darbo vietų. Šiandien yra daug programinės įrangos prisijungimui per VPN, panaudojant RSA raktų generatorius ir pan. Tačiau visi šie sprendimai dažniausiai yra brangūs ir ne kiekvienai kompanijai prieinami. Šio darbo tikslas – sukurti atviru kodu paremtą nemokamą sistemą darbui su nutolusiu serveriu, kurioje būtų skiriamas ypatingas dėmesys vartotojų autentifikavimui. / Administration of servers is responsible job and has to take into account security issues to ensure server reliability. In this work server security issues are analyzed and requirements for system of mobile server management are defined as well as architecture specification is described. The system uses three security factors and allows management of main server functions. It uses just open source solutions and can be used with different mobile devices which allow wider system usage. The made system testing proves system reliability while detailed manual increases system usage simplicity.

Šio darbo tikslas buvo sukurti reikalavimais grindžiamą duomenų saugumo ir matomumo metodų pasirinkimo bei jų kombinavimo metodinę medžiagą. Pateikti reikalavimas grindžiamą kompleksinės saugos modelį. Pašalinti kompleksinės apsaugos metodų informacijos trūkumą. Darbe išnagrinėti ir palyginti garsių pasaulio saugos specialistų kompleksinės saugos sprendimai. Atlikta sistemos pažeidimų analizė ir sisteminimas. Darbe buvo siekiama atskleisti svarbiausius pažeidimus, jų veikimo principus ir kaip nuo jų tinkamai apsisaugoti. Praktinėje dalyje aprašytas kompleksinis saugos modelis, kuris vėliau smulkinamas į detalius apsaugos modelius. Modelis buvo pritaikytas šiandien populiariausiose kombinuotoje sistemose Microsoft Windows Server 2008 serveryje ir Microsoft SQL Server 2008 duomenų bazių valdymo sistemoje. Naudojantis metodika galima atlikti esamos sistemos saugumo analizę ir remiantis veiklos modeliais teisingai konfigūruoti esamą ar naujai kuriamą sistemą. / This work destination was to create requirements based on data security and availability method choosing and their combination methodology. Introduce requirements based on complex security model. Eliminate information lack of complex security. In work analyzed and compared complex security solutions of famous the word security specialists. Accomplished system vulnerability analysis and systematized information. During the work revealed most important vulnerabilities, explain how it works and how correctly secure of them. In this research described security model of complex security, which later detailed as smaller part of model. Complex security model were used at nowadays most popular combined information system. For research were used Microsoft Windows Server 2008 and Microsoft SQL Server 2008. Created methodology is useful then necessary to test existing or creating new configuration of system.

Bakalauro baigiamajame darbe buvo sukurtas mobilus žiniatiklio serveris su PostgreSQL ir PHP, bei papildomais moduliais. Buvo atlikta panašių sistemų analizė. Buvo sukurta reikalavimų specifikacija, architektūros specifikacija aliktas testavimas, sukurtas vartotojo ir diegimo vadovas. / Aim of the work – to develop a mobile (portable) web server software with PHP, PostgreSQL and other modules. In this work you can find analysis of others mobile web servers, some information about existing solutions, established requirements for servers software. Based on system requirements specification and architectural specification system testing was conducted in order to find and fix system errors and also check system compatibility with different MS Windows operating systems. User manual is also added.

No description available.

Šio darbo tikslas – išanalizuoti pasirinktas rinkmenų paieškos sistemas bei pasirinkta optimaliausia metodika sukurti elektroninių dokumentų paieškos sistemą, kuri leistų sumažinti laiko sanaudas ieškant rinkmenų vietinio tinklo serveryje ir vietiniame tinkle sujungtuose kompiuteriuose. Darbe aprašytos elektroninių dokumentų savybės, paieškos metodikos teoriniai ir praktiniai aspektai. Atlikta pasirinktų rinkmenų paieškos sistemų lyginamoji analizė. Šio tyrimo problema: vidutinio dydžio įmonėje ar įstaigoje sunku greitai surasti ir peržiūrėti dokumentus, naudojamus vietiniame serveryje ar tinklo kompiuteriuose. Išanalizavus elektroninių dokumentų savybes bei jų paieškos technologijas buvo sukurta rinkmenų paieškos programa, pasinaudojant "Microsoft Visual C # 2005 Express Edition" programavimo platforma. Sukurta programa "Paieška", skirta surasti rinkmenas vietinio tinko serveryje ir tinklo kompiuterių bendrai naudojamuose kataloguose. Tai ypač naudinga organizacijose, besinaudojančiose bendrais dokumentų resursais. Darbą sudaro įvadas, elektroninių dokumentų analizė, rinkmenų paieškos sistemų analizė, paieškos technologijų apžvalga, realizuotos paieškos sistemos aprašymas, išvados, literatūros sąrašas ir 2 priedai. Darbo dydis yra 35 puslapiai be priedų, 3 lentelės, 4 paveikslėliai ir 17 literatūros šaltinių. / This work main purpose to analyze the usage of main desktop search systems, choose one optimal system and to create electronic documents search engine, which would reduce the time searching for files on a local network server and LAN computers. There are described document search and managemant teoretical and practical aspects. Develope essential features, accomplished comparable analysis of main document search systems. The following problems ware determined: there are no possibilities to find quickly and modify documents which are shared over Local Area Network in medium organization. After analysis of data search technologies it was decided to create a file search application using „Microsoft Visual C# 2005 Express Edition“ programming platform. Created application „Paieška“ is a tool designed for the purpose of searching for files and folders which are shared over a Local Area Network and servers. It is particularly useful in organizations where a lot of folders are shared on individual systems. The work consists of introduction, the analysis of data managemant usage in the document management system, technologies of document seaching, solution for document search system, findings, references and 2 annexes. The size of work is 35 pages without annexes, 3 tables, 4 pictures and 17 references.

<p>Trends in increasing web traffic demand an increase in server throughput while preserving energy efficiency and total cost of ownership. Present work in optimizing data center efficiency primarily focuses on using general purpose processors, however these might not be the most efficient platforms for server workloads. Data parallel hardware achieves high energy efficiency by amortizing instruction costs across multiple data streams, and high throughput by enabling massive parallelism across independent threads. These benefits are considered traditionally applicable to scientific workloads, and common server tasks like page serving or search are considered unsuitable for a data parallel execution model.</p><p>Our work builds on the observation that server workload execution patterns are not completely unique across multiple requests. For a high enough arrival rate, a server has the opportunity to launch cohorts of similar requests on data parallel hardware, improving server performance and power/energy efficiency. We present a framework---called Rhythm---for high throughput servers that can exploit similarity across requests to improve server performance and power/energy efficiency by launching data parallel executions for request cohorts. An implementation of the SPECWeb Banking workload using Rhythm on NVIDIA GPUs provides a basis for evaluation. </p><p>Similarity search is another ubiquitous server workload that involves identifying the nearest neighbors to a given query across a large number of points. We explore the performance, power and dollar benefits of using accelerators to perform similarity search for query cohorts in very high dimensions under tight deadlines, and demonstrate an implementation on GPUs that searches across a corpus of billions of documents and is significantly cheaper than commercial deployments. We show that with software and system modifications, data parallel designs can greatly outperform common task parallel implementations.</p> / Dissertation