軟體即服務（Software as a Service, SaaS）是雲端運算環境下一種新興的服務模式，它的特色是將特定的應用軟體以共享軟硬體資源的方式供眾多的租戶（tenants）使用。因此，如何提供共用且有客制化功能的應用軟體就是SaaS模式的重要成功關鍵。本研究聚焦於資料庫層提供多租戶共用表格但有客制化功能的機制。讓開發人員延續一租戶一資料表的架構為基礎設計資料庫，透過SQL語句轉換機制，將SQL語句轉換為操作共享表格的語句執行，以大幅減化開發人員的工作。本研究包含兩個部份，一是資料綱要對應表(Schema Mapping Table)，協助開發人員將單租戶資料庫架構轉換為塊狀表格(chunk table)的共用資料綱要方式；另一個是SQL語句自動轉換工具，透過剖面技術織入JDBC程式集中，在應用系統執行期間，將SQL語句，從一租戶一資料表寫法轉換為共享表格的方式執行。故只需將資料表改為共用架構即可使用，達到提升多租戶系統開發速度並提高資源使用率的目的。 / Software as a service (SaaS) is an emerging service model of cloud computing, which is characterized by providing software that charges on a usage basis over shared hardware and software resources for a large number of tenants to use. Therefore, how to provide shared tables and customization of the applications is an important key to success in the SaaS model. This study focuses on how to enable multi-tenancy on the database layer Developers can extend a private table structure-based application to a shared database one through the proposed SQL rewriting mechanism. This approach can greatly simplify the developer's work. Our approach consists of two parts, first is Schema Mapping Table that helps developers to convert single-tenant database architecture into the chunk table schema; another is SQL statement conversion tools that works by enhancing the JDBC library as an aspect in the AspectJ language. During the execution of the application, a SQL statement is rewritten from the private table based format into chunk table based statement. In this way, we are able to enhance an application with multitenant shared tables that improve resource utilization.

A Multi-tenant architecture is a cost optimization for Software as a Service, where customers, also referred to as tenants are consolidated into the same server. The main idea of this architecture is to consolidate as many tenants as possible into the same server to reduce the total cost for the service provider. However, the contention of shared resources can lead to reduced performance for the tenants. One shared resource between the tenants is the data-layer.This thesis aims to analyze and to do a performance evaluation of different data-layer designs in a Multi-tenant architecture. The thesis compares three data-layer designs implemented in a RDBMS.An experiment was performed to evaluate the transactions per secondfor tenants when both the amount of data and the number of tenants increase. The evaluations were computed for the Create, Read, Update and Delete operations, also known as the CRUD-operations.Three data-layer designs were tested in the experiment; Shared table design, where tenants share the same database system as well as the tables, Separated table design, where tenants share the same database system but store and query data to their own private tables and Oracle Multi-tenant, where each tenant gets its own database.The experiment indicates that the Oracle Multi-tenant has the highest performance while the Shared table design suffers when both the number of tenants and the amount of data increase. / Multi-tenant arkitektur är en kostnadsoptimering för mjukvara som tillhandahålls över ett nätverk. Användarna, tenants är då betjänade av samma serverdator. Uppdraget för serverdatorn är att betjäna så många tenants som möjligt för att reducera kostnader för mjukvaruägaren. Men att dela resurser mellan tenants kan leda till försämrad prestanda. En delad resurs mellan tenants är dataskiktet.Målet med denna uppsats är att göra en analys och ett prestandatest av olika uppsättningar av dataskikt i en Multi-tenant arkitektur. Uppsatsen fokuserar endast på olika uppsättningar i ett RDBMS.Ett experiment utfördes där antalet tenants och data ökade för varje uppsättning. Experimentet evaluerade prestanda av Create, Read, Update och Delete operationer, även känt som CRUD-operationer. Tre uppsättningar testades; Shared table design, där tenants delar databas och tabeller, Separated table design, där tenants delar databas, men lagrar data i sina egna tabeller och Oracle Multi-tenant, där varje tenant får en egen databas.Experiment visar att Oracle Multi-tenant har högst prestanda medan Shared table design har lägst när antalet tenants och mängd data ökar.

Data centres lie at the heart of almost every service on the Internet. Data centres are used to provide search results, to power social media, to store and index email, to host “cloud” applications, for online retail and to provide a myriad of other web services. Consequently the more efficient they can be made the better for all of us. The power of modern data centres is in combining commodity off-the-shelf server hardware and network equipment to provide what Google’s Barrosso and Ho ̈lzle describe as “warehouse scale” computers. Data centres rely on TCP, a transport protocol that was originally designed for use in the Internet. Like other such protocols, TCP has been optimised to maximise throughput, usually by filling up queues at the bottleneck. However, for most applications within a data centre network latency is more critical than throughput. Consequently the choice of transport protocol becomes a bottleneck for performance. My thesis is that the solution to this is to move away from the use of one-size-fits-all transport protocols towards ones that have been designed to reduce latency across the data centre and which can dynamically respond to the needs of the applications. This dissertation focuses on optimising the transport layer in data centre networks. In particular I address the question of whether any single transport mechanism can be flexible enough to cater to the needs of all data centre traffic. I show that one leading protocol (DCTCP) has been heavily optimised for certain network conditions. I then explore approaches that seek to minimise latency for applications that care about it while still allowing throughput-intensive applications to receive a good level of service. My key contributions to this are Silo and Trevi. Trevi is a novel transport system for storage traffic that utilises fountain coding to max- imise throughput and minimise latency while being agnostic to drop, thus allowing storage traffic to be pushed out of the way when latency sensitive traffic is present in the network. Silo is an admission control system that is designed to give tenants of a multi-tenant data centre guaranteed low latency network performance. Both of these were developed in collaboration with others.

The diploma thesis deals with the definition of transformation process of the "appropriate" application into Software as a Service (SaaS) distribution model. For this purpose, it describes the SaaS model and evaluates its pros and cons in four points of view -- developer, distributor, customer and user. Following parts of the model description are an estimation of the future evolution of the SaaS model, the introduction of application SaaS Platforms and the specification of appropriate application for the SaaS model. Next chapter deals with the specifications of the application distributed in the Software as a Service model. These specifications define all needed application properties that have to be implemented in the transformation process. These specifications are for example differentiation of customer data and administration access, configuration and customization, application and data security, business and pricing model, service level agreement etc. The last chapter deals with the formulation of the transformation process of the application into SaaS model. Individual activities of the process are closely described and demonstrated on the preparation of details for the transformation of the web-based application Audit Information Tracker into SaaS model.

<p>Sve češćom upotrebom cloud okruženja dolazi do potrebe da se postojeća softverska rešenja migriraju. Metodologija za migraciju na cloud postoji više, gde se u finalnim fazama planiraju modifikacije nad arhitekturom softvera tako da se iskoriste prednosti cloud sistema. Za ekonomsku efikasnost usled uštede resursa je neophodna višeorganizacijska osobina. Svrha ovog istraživanja je da pojasni višeorganizacijsko svojstvo i da predloži rešenje za migraciju postojećih softvera na višeorganizacijski SaaS ali sa što manje neophodnih modifikacija ciljnog softvera. S toga je predloženo rešenje platforma koja omogućuje lakšu migraciju. Nakon faze istraživanja i sagledavanja domena pametnih elektroenergetskih mreža, kreiran je prototip predloženog rešenja kao i niz eksperimenata u skladu sa definisanim naučnim pitanjima. Eksperimenti su izvršeni u privatnom cloud okruženju. Hipoteze su adresirane kroz viziju primene rešenja na NDMS (Napredni distributivni menadžment sistem) u slučaju šest organizacija, a doneti su sledeći zaključci: višeorganizacijskim modelom se ostvaruju uštede u resursima od 32%, za tri reda veličine veća visoka dostupnost, ali uz usporenja do 20 milisekundi po svakom servisnom zahtevu. Takođe, aplikativni model učesnika modernih PaaS usluga nije primeren gde je sinhronizam zahtevan, niti u slučajevima gde se očekuju odgovori nad skupom učesnika u realnom vremenu. Istraživanje ukazuje na mogućnost primene višeorganizacijskog modela čak i u slučaju kompleksnih rešenja kakva se sreću u domenu pametnih elektroenergetskih mreža, a akademskom validacijom potvrđuju način implementacije važnog finalnog koraka u procesu migracije softvera na cloud bazirani SaaS.</p> / <p>Progressive cloud adoption requires migration of existing software solutions. Today, many cloud adoption methodologies exist. Usually, the final phase in cloud adoption include software architecture modifications to make the most of the benefits of cloud computing, like multi-tenancy which enables economic efficiency. The aim of this research is to explain the multi-tenancy and to provide a solution for migration of existing software to multi-tenant SaaS while modifying the target software as little as possible. Therefore, the research proposes a platform that enables easier cloud adoption. After the research phase focused on a smart grid domain, the prototype was created with experiments targeting formulated research questions. The experiments were conducted in a private cloud environment. Research hypotheses were analyzed using hypothetical multi-tenant ADMS (Advanced Distribution Management System) in case of six tenants, with the following conclusions: multi-tenancy saves 32% of resources, it provides three orders of magnitude higher availability, but affects performances by introducing a delay of up to 20 milliseconds per service request. Also, reliable actors programing model used in modern PaaS services is not suitable in use cases with needs for synchronous behavior, nor in in use cases where querying a set of actors is needed in real time. The research demonstrates feasibility of applying multi-tenancy even in cases of complex software solutions like the ones in the smart grid domain. The proposed solution is academically validated and it can be used as a final important step in migration of existing software to cloud based multi-tenant SaaS.</p>

雲端運算環境的興起，軟體即服務(Software as a Service, SaaS)的營運模式也開始受到軟體開發商的注意，其中一項關鍵技術是支援多租戶的軟體開發。在設計多租戶應用程式時有許多需要考量的因素，包含每個租戶各自的客製化設定、資料安全性等等。本論文著重於資料層級的客製化部份，如何讓各個租戶之間可以共用資料庫，但又能提供租戶適度地更改其資料表綱要(schema)以達到客製化的需求。 為了解決資料層級客製化所面臨的問題，一種常見的作法是可延伸性表格(Extension Table Layout)。但是，在關聯式資料庫中實作可延伸性表格，軟體開發人員為了配合可延伸性表格的資料存放方式，所使用的SQL語句會變得相當複雜且易錯。因此，本研究實作一個系統工具協助軟體開發人員將SQL語句，從一租戶一資料表寫法自動轉換成以可延伸性表格邏輯表達的SQL語句，透過執行轉換後的語句來對儲存在可延伸性表格的資料進行增刪修改。 軟體開發人員在本系統工具的協助下，加入租戶識別碼(TenanId)的開發概念後，即可實際建立一個多租戶應用程式。為了評估本系統工具的效用，我們以其建置了一個多校(租戶)選課系統，並進行多項效能實驗以探討影響本系統工具效能的因素。初步的結果顯示，本系統工具可以協助軟體開發人員，以較低的代價滿足資料層級客製化應用的需求。 / Software as a service (SaaS) is an emerging service model of cloud computing. One of the key technology in SaaS is supporting multi-tenant applications. There are many considerations in the design of multi-tenant applications, including customized configuration of tenants and data security. In this thesis, we focus on data-level customized configuration, and propose an approach for not only sharing database between tenants but also supporting tenants to modify their table schemas within limits. Extension Table Layout is one solution for solving the problems in data-level customized configuration for multi-tenant applications. However, SQL statemenst based on the Extension Table Layout are rather complicated and error-prone. Thus, we develop a tool to help software developers that will automatically rewrite the SQL statements from the common Private Table Layout into those from the Extension Table Layout at runtime. In other words, our tool enable software developers to write SQL statements in a multi-tenant application like in a single tenant application. Indeed, software developers could develop a multi-tenant application easily by using our tool and the multi-tenant enabler - TenantId. In order to assess the feasibility of our tool, we develop an online multi-tenant course election application. Besides, we disscus the effectiveness of the factors that affecting our tool and work on a number of experiments and performance tests. The preliminary results show that our SQL rewriting tool can help software developers at a lower cost to meet the needs of data-level customized applications to a degree.

A Multi-tenant database (MTD) is a way of deploying a Database as a Service (DaaS). A multi-tenant database refers to a principle where a single instance of a Database Management System (DBMS) runs on a server, serving multiple clients organisations (tenants). This technology has helped to discard the large-scale investments in hardware and software resources, in upgrading them regularly and in expensive licences of application software used on in-house hosted database systems. This is gaining momentum with significant increase in the number of organisations ready to take advantage of the technology. The benefits of MTD are potentially enormous but for any organisation to venture into its adoption, there are some salient factors which must be well understood and examined before venturing into the concept. This research examines these factors, different models of MTD, consider the requirements and challenges of implementing MTDs. Investigation of the degree of impact each of these factors has on the adoption of MTD is conducted in this research which focused mainly on public organisations. The methodology adopted in undertaking this study is a mixed method which involved both qualitative and quantitative research approaches. These strategies are used here to cover statistics (quantifiable data) and experts’ knowledge and experiences (abstract data) in order to satisfactorily achieve the aim and objectives and complete the research. Following the involvement of these strategies, a framework was developed and further refined after a second survey was carried out with a quantitative approach. This framework will help prospective tenants to make informed decisions about the adoption of the concept. The research also considers the direction of decisions about MTDs in situations where two or more factors are combined. A new MTD framework is presented that improves the decision making process of MTD adoption. Also, an Expert System (ES) is developed from the framework which was validated via a survey and analysed with the aid of SPSS software. The findings from the validation indicated that the framework is valuable and suitable for use in practice since majority of respondents accepted the research findings and recommendations for success. Likewise, the ES was validated with majority of participants accepting it and embracing the high level of its friendliness.

近年來雲端運算蓬勃發展，為資訊系統的建置與服務帶來巨大的改變，其中一個重要趨勢為軟體即服務，並透過多租戶共享資源達到降低成本的優勢。因此如何讓服務可以共享資源，又能兼顧各租戶的客製化需求，這將會是軟體即服務關鍵成功因素。 為了讓租戶客製化自己的綱要，在多租戶的相關研究中，發展出各種綱要映射技術，各適用不同的狀況，但在開發應用程式時候往往無法預估租戶適合使用何種綱要映射技術。本研究提出可以讓多租戶軟體框架具有綱要映射技術的可調性，應用程式開發時候毋需考慮使用何種綱要映射技術，等租用時候再依據應用程式及租戶的特性決定。本研究將以小量租戶效能最佳的Private Table Layout與適合用於大量租戶的Universal Table Layout為例，提出的可調性多租戶實體模式來建構具有可調性的多租戶軟體框架。此外本研究提出的軟體框架經過技術的封裝，開發者不需要了解多租戶的相關技術，就能完成多租戶應用程式的開發。 / Software as a service (SaaS) is an emerging service model of cloud computing. It’s central defining characteristic is the ability for clients to use a software application on a pay-as-you-go subscription basis. However, to be economically sustainable, a SaaS application must leverage resource sharing to a large degree by accommodating different clients of the application while making it appear to each that they have the application all to themselves. In other words, a SaaS application must be a multi-tenant application. An important multi-tenant research topic is the various kinds of schema mapping technology have been developed in order for our tenants to customize their schema. However, it is hard to determine tenants’ need for particular schema mapping technology in different circumstances. This thesis proposes an adaptable schema mapping technology for a multi-tenant application (MTA) framework. The application and tenants’ characteristics do not need to be considered while applications developers are developing their schema mapping technology. This approach will take examples from the Private Table Layout mapping and the Universal Table Layout mapping to illustrate the features of this adaptable multi-tenant software framework. Furthermore, this thesis argues that, with the approach packaged as a software framework, developers are able to complete the development of a multi-tenant application without full understanding of the underlying technologies.

隨著雲端運算的服務租用理念越來越受到重視，SaaS 服務供應商在提供服務的時候無不希望可以以最少的成本服務最多的客戶，於是吸引了許多的研究者投入精力以及時間，希望可以設計出讓租戶們共享資源又能夠有客製化空間的解決方案。服務供應商為了順利推廣多租戶軟體開發，其中一項關鍵技術是支援 SQL 語句自動轉換機制，目的是協助 SQL 語句轉換成以多租戶資料架構邏輯表達的 SQL 語句，讓租戶應用程式的軟體開發人員能夠專注在自身的應用程式開發。 開發 SQL 語句自動轉換機制，必須先選定資料庫的資料架構，本論文採用 Universal Table Layout 這個 SaaS 多租戶資料共享常見的資料架構。 我們參考知名 SaaS 廠商 Force.com 的 Universal Table Layout 資料架構，並提出一些修正。其次，我們應用關聯式代數抽象化來設計 SQL 語句的轉換規則，這些理論結果不僅在表達轉換機制上更具有一般性，並且讓轉換規則的理解也變得更加容易。我們以這些理論推導為基礎實現一個實驗的工具，最後透過幾個實驗，觀察及探討實驗數據所呈現的意義。

AbstractStörre bolag är inte lika aktiva som små till medelstora bolag när det gäller att migrera sitt affärssystem till molnet. Små till medelstora bolag migrerar i allt större utsträckning sina affärssystem till molnet. Större bolag verkar dock inte kunna få ut samma effekter som de mindre bolagen av att använda molnbaserade affärssystem.Syftet med denna kandidatuppsats i Informatik är att identifiera, beskriva och förklara faktorer som bromsar större bolag att migrera till molnbaserade affärssystem. Med större bolag menas organisationer med fler än 250 anställda och/eller en omsättning större än 500 miljoner kronor.Studien har haft ett explorativt angreppssätt. Primära empiriska data har insamlats genom kvalitativa intervjuer och observationer. Fyra respondenter har intervjuats angående deras uppfattningar om vilka faktorer som är bromsande för de större bolagens migrering till molnbaserade affärssystem. Respondenterna har olika arbetsbakgrunder inom ämnet molnbaserade affärssystem: En IT-chef, en affärssystemskonsult, en lösningsarkitekt, samt en utbildare inom molnbaserade affärssystem. Analysen baseras därför på primära empiriska data från olika rollinnehavare med olika perspektiv på de bromsande faktorerna för större bolags migrering.De viktigaste slutsatserna som dras utifrån uppsatsstudiens analys är: att datasäkerheten inte längre uppfattas vara en bromsande faktor för större bolags migrering till molnbaserade affärssystem. Produktpaketeringen avseende funktionalitet och pris skulle behöva bli mer gynnsam för de större bolagen gällande molnbaserade affärssystem. Förändringar i företagets systeminfrastruktur är inte en bromsande faktor för de större bolagen eftersom större bolag sällan har affärssystemet infrastruktur som är ”på plats”.