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Prior work in the transformational leadership realm has focused primarily on relations among leader behaviors and various criteria such as subordinate satisfaction and effectiveness. This restrictive focus has limited the degree to which one of Bass's (1985a) central arguments can be directly assessed; namely, that optimally effective leaders engage in both transformational and transactional behaviors. In this study, an analytic technique known as the pattern approach was employed to effectively discern which particular pattern of leader behaviors was associated with the highest levels of subordinate satisfaction and commitment. In general, the most effective leaders used a combination of transformational (e.g., stimulating subordinates to think of old problems in new ways; presenting a charismatic and inspirational view of the future) and contingent reward (e.g., providing pay or promotions in exchange for effective subordinate performance) behaviors, coupled with a low level of passive management-by-exception behaviors (e.g., remaining uninvolved until problems emerge). These optimally effective leaders were generally more successful than leaders who used predominantly one (e.g., transformational or transactional) behavioral style. / Ph. D.

It has historically been the case that CPUs have run programs ever faster without significant intervention on the behalf of the programmer. However, this "free lunch" has largely ended due to the end of exponentially increasing core frequency and the current slow increase in instruction-level parallelism but continues to a degree in cache size improvements. But since Moore's law still largely continues "lunch", i.e. program performance, can still be bought at the price of rewriting code for multiple cores, which is enabled by the trend Moore's law describes. Multicore architectures cannot aid performance for problems whose solutions are necessarily sequential in nature and writing efficient and correct concurrent programs is not easy in all cases when using synchronization methods like fine-grained mutex locks. Transactional memory, and its implementation as hardware transactional memory, allow programmers to write concurrent applications without the attendant complexity of programming with mutex locks. This allows programmers to focus on optimizing the application for performance. Given that transactions can run two segments of code in parallel that a mutex lock would force to run sequentially and that transactions can abort, causing a program to do the same work more than once, whether transactions perform better or worse than mutex locks is dependent on the program's execution profile and the coarseness or fineness at which mutex locks are used. In this thesis the GNU C Library's futex implementation of mutex locks and Intel's Restricted Transactional Memory have been compared and the behavior of those transactions has been analyzed. This analysis includes a pathological behavior permitted by the GNU C Library's hardware transactional memory implementation of mutex locks. The tradeoffs between fine-grained and global locking implementations have been discussed, compared, and used in the context of fallback locks for hardware transactions. This thesis provides evidence to the effect that fine-grained locking is not critical for program performance and that in many cases global locking and hardware transactions can provide nearly equivalent performance without the programming difficulties. This work has shown that across the 23 applications examined, with relation to their original locking implementation, a global locking scheme without elision has a 0.96x speedup, Intel's Restricted Transactional Memory (RTM) with the application's original locks as a fallback has a 1.01x speedup and with global lock fallback RTM has a speedup of 0.97x. This work is supported in part by NAVSEA/NEEC under grant 3003279297. Any opinions, findings, and conclusions or recommendations expressed in this thesis are those of the author and do not necessarily reflect the views of NAVSEA. / Master of Science

Distributed Transactional Memory (DTM) is an emerging synchronization abstraction thatpromises to alleviate the scalability, programmability, and composability challenges of lock-based distributed synchronization. With DTM, programmers organize code that read/writeshared memory objects, both local and remote, as memory transactions. An underlying DTMframework guarantees atomicity, isolation, and consistency properties for those transactionsthrough speculative concurrency control. In DTM, restarting an aborted transaction from the beginning can degrade performance astransactional conflicts may have occurred in the later part of the transaction, wasting work.The partial abort method alleviates this difficulty by enabling a transaction to be rolled backto the point where objects in the transaction's read-set and write-set are still consistent.In this thesis, we present protocols for supporting partial aborts in QR-DTM, a fault-tolerant DTM that uses quorum protocols for distributed concurrency control in the presence offailures. We focus on two partial abort models: closed nesting, which allows transactions to be nested and inner transactions to be rolled back without rolling back outer transactions;and checkpointing, which allows the transaction state to be saved in checkpoints throughout execution and transactions to be rolled back to those checkpoints. We present protocols that support these partial abort models in QR-DTM, called QR-CN and QR-CHK. We implemented these protocols and conducted experimental studies using macro-benchmarks(e.g., distributed versions of STAMP benchmark), and micro-benchmarks (e.g., distributed data structures). Our studies reveal that QR-CN improves throughput by as much as 101% over flat nesting in specific cases, with an average improvement of 53%. We also develop QR-ACN, a framework that automatically decomposes programmer-writtentransactions into closed nested transactions, at run-time, to improve performance. The composition of a closed nested transaction depends on the contention of objects, which can change at run-time depending upon the workload at hand. Our implementation and experimental studies reveal that QR-ACN consistently outperforms flat nesting by an averageof 51% on benchmarks including TPC-C. False conflicts occur when high-level operations, even though semantically independent, traverse the same set of objects during transaction execution. Such conflicts can lead torepeated aborts, increasing transaction execution time and degrading performance, which can be significant in DTM, since transaction execution also includes network communication. ii We consider the approach of reducing validation cost for resolving false conflicts. We presentthree protocols for reducing validation cost in DTM. Our first protocol, QR-ON, incorporatesthe open nesting model into QR-DTM. Open nesting allows inner-nested transactions tocommit independently of their parent transaction, releasing objects in the transaction read-set and write-set early, minimizing aborts due to false conflicts. We then present QR-OON,in which open-nested transactions commit asynchronously so that subsequent transactionscan proceed without waiting for the commit of previous transactions. Finally, we presentan early release methodology, QR-ER, in which objects that do not affect the final state ofthe shared data are dropped from the transaction's read-set, which avoids false conflicts andreduces communication costs. Our implementation and experimental studies revealed that QR-OON outperforms QR-ON by up to 43%, and that QR-ER outperforms QR-ON and QR-OON by up to 10% on micro- and macro-benchmarks. / Master of Science

Distributed Transactional Memory (DTM) is an emerging, alternative concurrency control model that aims to overcome the challenges of distributed-lock based synchronization. DTM employs transactions in order to guarantee consistency in a concurrent execution. When two or more transactions conflict, all but one need to be delayed or rolled back. Transactional Memory supports code composability by nesting transactions. Nesting how- ever can be used as a strategy to improve performance. The closed nesting model enables partial rollback by allowing a sub-transaction to abort without aborting its parent, thus reducing the amount of work that needs to be retried. In the open nesting model, sub- transactions can commit to the shared state independently of their parents. This reduces isolation and increases concurrency. Our first main contribution in this dissertation are two extensions to the existing Transac- tional Forwarding Algorithm (TFA). Our extensions are N-TFA and TFA-ON, and support closed nesting and open nesting, respectively. We additionally extend the existing SCORe algorithm with support for open nesting (we call the result SCORe-ON). We implement these algorithms in a Java DTM framework and evaluate them. This represents the first study of transaction nesting in the context of DTM, and contributes the first DTM implementation which supports closed nesting or open nesting. Closed nesting through our N-TFA implementation proved insufficient for any significant throughput improvements. It ran on average 2% faster than flat nesting, while performance for individual tests varied between 42% slowdown and 84% speedup. The workloads that benefit most from closed nesting are characterized by short transactions, with between two and five sub-transactions. Open nesting, as exemplified by our TFA-ON and SCORe-ON implementations, showed promising results. We determined performance improvement to be a trade-off between the overhead of additional commits and the fundamental conflict rate. For write-intensive, high- conflict workloads, open nesting may not be appropriate, and we observed a maximum speedup of 30%. On the other hand, for lower fundamental-conflict workloads, open nesting enabled speedups of up to 167% in our tests. In addition to the two nesting algorithms, we also develop Hyflow2, a high-performance DTM framework for the Java Virtual Machine, written in Scala. It has a clean Scala API and a compatibility Java API. Hyflow2 was on average two times faster than Hyflow on high-contention workloads, and up to 16 times faster in low-contention workloads. Our second main contribution for improving DTM performance is automated data partition- ing. Modern transactional processing systems need to be fast and scalable, but this means many such systems settled for weak consistency models. It is however possible to achieve all of strong consistency, high scalability and high performance, by using fine-grained partitions and light-weight concurrency control that avoids superfluous synchronization and other over- heads such as lock management. Independent transactions are one such mechanism, that rely on good partitions and appropriately defined transactions. On the downside, it is not usually straightforward to determine optimal partitioning schemes, especially when dealing with non-trivial amounts of data. Our work attempts to solve this problem by automating the partitioning process, choosing the correct transactional primitive, and routing transactions appropriately. Our third main contribution is Alvin, a system for managing concurrently running trans- actions on a geographically replicated data-store. Alvin supports general-purpose transactions, and guarantees strong consistency criteria. Through a novel partial order broadcast protocol, Alvin maximizes the parallelism of ordering and local transaction processing, resulting in low client-perceived latency. Alvin can process read-only transactions either lo- cally or globally, according to the desired consistency criterion. Conflicting transactions are ordered across all sites. We built Alvin in the Go programming language. We conducted our evaluation study on Amazon EC2 infrastructure and compared against Paxos- and EPaxos- based state machine replication protocols. Our results reveal that Alvin provides significant speed-up for read-dominated TPC-C workloads: as much as 4.8x when compared to EPaxos on 7 datacenters, and up to 26% in write-intensive workloads. Our fourth and final contribution is M2Paxos, a multi-leader implementation of Generalized Consensus. Single leader-based consensus protocols are known to stop scaling once the leader reaches its saturation point. Ordering commands based on conflicts is appealing due to the potentially higher parallelism, but is imperfect due to the higher quorum sizes required for fast decisions and the need to compare commands and track their dependencies. M2Paxos on the other hand exploits fast decisions (i.e., delivery of a command in two communication delays) by leveraging a classic quorum size, matching a majority of nodes deployed. M2Paxos does not establish command dependencies based on conflicts, but it binds accessed objects to nodes, making sure commands operating on the same object will be ordered by the same node. Our evaluation study of M2Paxos (also built in Go) confirms the effectiveness of this approach, getting up to 7⨉ improvements in performance over state- of-the-art consensus and generalized consensus algorithms. / Ph. D.

As chip vendors are increasingly manufacturing a new generation of multi-processor chips called multicores, improving software performance requires exposing greater concurrency in software. Since code that must be run sequentially is often due to the need for synchronization, the synchronization abstraction has a significant effect on program performance. Lock-based synchronization — the most widely used synchronization method — suffers from programability, scalability, and composability challenges. Transactional memory (TM) is an emerging synchronization abstraction that promises to alleviate the difficulties with lock-based synchronization. With TM, code that read/write shared memory objects is organized as transactions, which speculatively execute. When two transactions conflict (e.g., read/write, write/write), one of them is aborted, while the other commits, yielding (the illusion of) atomicity. Aborted transactions are re-started, after rolling-back changes made to objects. In addition to a simple programming model, TM provides performance comparable to lock-based synchronization. Software transactional memory (STM) implements TM entirely in software, without any special hardware support, and is usually implemented as a library, or supported by a compiler or by a virtual machine. In this thesis, we present ByteSTM, a virtual machine-level Java STM implementation. ByteSTM implements two STM algorithms, TL2 and RingSTM, and transparently supports implicit transactions. Program bytecode is automatically modified to support transactions: memory load/store bytecode instructions automatically switch to transactional mode when a transaction starts, and switch back to normal mode when the transaction successfully commits. Being implemented at the VM-level, it accesses memory directly and uses absolute memory addresses to uniformly handle memory. Moreover, it avoids Java garbage collection (which has a negative impact on STM performance), by manually allocating and recycling memory for transactional metadata. ByteSTM uses field-based granularity, and uses the thread header to store transactional metadata, instead of the slower Java ThreadLocal abstraction. We conducted experimental studies comparing ByteSTM with other state-of-the-art Java STMs including Deuce, ObjectFabric, Multiverse, DSTM2, and JVSTM on a set of micro- benchmarks and macro-benchmarks. Our results reveal that, ByteSTM's transactional throughput improvement over competitors ranges from 20% to 75% on micro-benchmarks and from 36% to 100% on macro-benchmarks. / Master of Science

This study proposes and evaluates a new method for Web archiving. We leverage the caching infrastructure in Web servers for archiving. Redis is used as the page cache and its persistence mechanism is exploited for archiving. We experimentally evaluate the performance of our archival technique using the Greek version of Wikipedia deployed on Amazon cloud infrastructure. We show that there is a slight increase in latencies of the rendered pages due to archiving. Though the server performance is comparable at larger page cache sizes, the maximum throughput the server can handle decreases significantly at lower cache sizes due to more disk write operations as a result of archiving. Since pages are dynamically rendered and the technology stack of Wikipedia is extensively used in a number of Web applications, our results should have broad impact. / Master of Science / This study proposes and evaluates a new method for Web archiving. To reduce response time for serving webpages, Web Servers store recently rendered pages in memory. This process is known as caching. We modify this caching mechanism of Web Servers for archival. We then experimentally evaluate the impact of our archival technique on Web Servers. We observe that the time to render a Web page increases slightly as long as the Web Server is under moderate load. Through our experiments, we establish limits on the maximum requests a Web Server can handle without increasing the response time. We ensure our experiments are conducted on Web Servers using technologies that are widely used today. Thus our results should have broad impact.

A firma é um agente econômico complexo. Este agente tem sido estudado através de diferentes teorias da firma. Enquanto alguns trabalhos destacaram a sua natureza tecnológica, outros enfatizaram a sua natureza transacional. Contudo, a natureza da firma abrange ambas as dimensões. Essas duas dimensões podem ser estudadas por meio de duas capacidades essenciais: a tecnológica e a transacional. O objetivo da presente tese é o de descrever como a combinação entre a capacidade tecnológica e a capacidade transacional geram os ativos específicos para que a firma alcance um desempenho superior ao de suas concorrentes. Para cumprir com esse objetivo, foi elaborado um modelo baseado em quatro pressupostos teóricos: as capacidades são heterogêneas; há uma trajetória transacional além da trajetória tecnológica; as capacidades não são transacionáveis e as capacidades antecedem os ativos específicos. O modelo também é composto por quatro construtos: capacidade tecnológica; capacidade transacional; ativos específicos; e desempenho. O método para testar esse modelo foi descritivo, utilizando-se como técnica para coleta de dados a survey. O objeto de estudo escolhido foi o do setor metal-mecânico do Rio Grande do Sul. Três dos resultados obtidos são os seguintes: (1) a relação entre as capacidades essenciais (tecnológica e transacional) e os ativos específicos é positiva e elevada, o que indica a grande ligação entre esses dois construtos; (2) a relação entre os ativos específicos e o desempenho da firma é maior do que a relação entre as capacidades essenciais e os ativos específicos; (3) a relação da combinação das capacidades essenciais e dos ativos específicos com o desempenho da firma é maior do que a relação entre o desempenho da firma e algum destes construtos, quando estas relações são analisadas de maneira isolada. As implicações teóricas desses resultados confirmam que a firma tem uma natureza tecnológico-transacional. Além disso, os estudos a respeito do desempenho da firma não mais deveriam dedicar-se somente a analisar suas capacidades; antes, deveriam abranger os ativos específicos, como elemento complementar. Finalmente, o fato de confirmar a existência de uma capacidade transacional como elemento-chave da natureza da firma abre uma nova possibilidade para se avançar rumo ao que, nesta tese, se denomina: Paradigma transacional. / A firm is a complex economic agent. This agent has been studied through different theories of the firm. While, some works underlined its technological nature, other works emphasized its transactional nature. However, the nature of the firm covers both dimensions. These two dimensions could be studied through two essential capabilities: the technological one and the transactional one. The objective of this thesis is to analyze the relation between the technological capability and the transactional capability, aiming to generate the assets specificity in order to reach firm’s superior performance compared to its competitors. For accomplishing that objective, it was elaborated a theoretical model based in four theoretical assumptions: capabilities heterogeneity, the existence of a transactional trajectory, besides the technological trajectory; the capabilities are not negotiable; and the capabilities are antecedents to the assets specificity. The model is also composed for four construction blocks: the technological capability, the transactional capability; the specific assets; and the performance. The method employed to test this model was descriptive, utilizing for its operability a survey. The chosen study objet was the Brazilian metal-mechanical sector. Three of the obtained results are the following ones: (1) A relation between the essential capabilities (technological and transactional) and the assets specificity is positive and high, indicating a big link between this two constructs; (2) The relation between the assets specificity and the firm performance is minor than the relation between the capabilities and the assets specificity; (3) a combinational relation of the essential capabilities and the assets specificity with the firm performance is bigger than the relation between the firm performance and some of these construction blocks, when these relations are analyzed in an isolated way. The theoretical implications of those results confirm that the firm has a technological-transactional nature. Furthermore, the studies related to the firm performance should not be devoted anymore just to analyze its capabilities; although, they should cover the assets specificity, as a complementary element. Finally, the fact of confirming the existence of a translational capability as a key element of the nature of the firm opens a new possibility for moving towards of what in this thesis is named as: Transactional paradigm.

A firma é um agente econômico complexo. Este agente tem sido estudado através de diferentes teorias da firma. Enquanto alguns trabalhos destacaram a sua natureza tecnológica, outros enfatizaram a sua natureza transacional. Contudo, a natureza da firma abrange ambas as dimensões. Essas duas dimensões podem ser estudadas por meio de duas capacidades essenciais: a tecnológica e a transacional. O objetivo da presente tese é o de descrever como a combinação entre a capacidade tecnológica e a capacidade transacional geram os ativos específicos para que a firma alcance um desempenho superior ao de suas concorrentes. Para cumprir com esse objetivo, foi elaborado um modelo baseado em quatro pressupostos teóricos: as capacidades são heterogêneas; há uma trajetória transacional além da trajetória tecnológica; as capacidades não são transacionáveis e as capacidades antecedem os ativos específicos. O modelo também é composto por quatro construtos: capacidade tecnológica; capacidade transacional; ativos específicos; e desempenho. O método para testar esse modelo foi descritivo, utilizando-se como técnica para coleta de dados a survey. O objeto de estudo escolhido foi o do setor metal-mecânico do Rio Grande do Sul. Três dos resultados obtidos são os seguintes: (1) a relação entre as capacidades essenciais (tecnológica e transacional) e os ativos específicos é positiva e elevada, o que indica a grande ligação entre esses dois construtos; (2) a relação entre os ativos específicos e o desempenho da firma é maior do que a relação entre as capacidades essenciais e os ativos específicos; (3) a relação da combinação das capacidades essenciais e dos ativos específicos com o desempenho da firma é maior do que a relação entre o desempenho da firma e algum destes construtos, quando estas relações são analisadas de maneira isolada. As implicações teóricas desses resultados confirmam que a firma tem uma natureza tecnológico-transacional. Além disso, os estudos a respeito do desempenho da firma não mais deveriam dedicar-se somente a analisar suas capacidades; antes, deveriam abranger os ativos específicos, como elemento complementar. Finalmente, o fato de confirmar a existência de uma capacidade transacional como elemento-chave da natureza da firma abre uma nova possibilidade para se avançar rumo ao que, nesta tese, se denomina: Paradigma transacional. / A firm is a complex economic agent. This agent has been studied through different theories of the firm. While, some works underlined its technological nature, other works emphasized its transactional nature. However, the nature of the firm covers both dimensions. These two dimensions could be studied through two essential capabilities: the technological one and the transactional one. The objective of this thesis is to analyze the relation between the technological capability and the transactional capability, aiming to generate the assets specificity in order to reach firm’s superior performance compared to its competitors. For accomplishing that objective, it was elaborated a theoretical model based in four theoretical assumptions: capabilities heterogeneity, the existence of a transactional trajectory, besides the technological trajectory; the capabilities are not negotiable; and the capabilities are antecedents to the assets specificity. The model is also composed for four construction blocks: the technological capability, the transactional capability; the specific assets; and the performance. The method employed to test this model was descriptive, utilizing for its operability a survey. The chosen study objet was the Brazilian metal-mechanical sector. Three of the obtained results are the following ones: (1) A relation between the essential capabilities (technological and transactional) and the assets specificity is positive and high, indicating a big link between this two constructs; (2) The relation between the assets specificity and the firm performance is minor than the relation between the capabilities and the assets specificity; (3) a combinational relation of the essential capabilities and the assets specificity with the firm performance is bigger than the relation between the firm performance and some of these construction blocks, when these relations are analyzed in an isolated way. The theoretical implications of those results confirm that the firm has a technological-transactional nature. Furthermore, the studies related to the firm performance should not be devoted anymore just to analyze its capabilities; although, they should cover the assets specificity, as a complementary element. Finally, the fact of confirming the existence of a translational capability as a key element of the nature of the firm opens a new possibility for moving towards of what in this thesis is named as: Transactional paradigm.

A firma é um agente econômico complexo. Este agente tem sido estudado através de diferentes teorias da firma. Enquanto alguns trabalhos destacaram a sua natureza tecnológica, outros enfatizaram a sua natureza transacional. Contudo, a natureza da firma abrange ambas as dimensões. Essas duas dimensões podem ser estudadas por meio de duas capacidades essenciais: a tecnológica e a transacional. O objetivo da presente tese é o de descrever como a combinação entre a capacidade tecnológica e a capacidade transacional geram os ativos específicos para que a firma alcance um desempenho superior ao de suas concorrentes. Para cumprir com esse objetivo, foi elaborado um modelo baseado em quatro pressupostos teóricos: as capacidades são heterogêneas; há uma trajetória transacional além da trajetória tecnológica; as capacidades não são transacionáveis e as capacidades antecedem os ativos específicos. O modelo também é composto por quatro construtos: capacidade tecnológica; capacidade transacional; ativos específicos; e desempenho. O método para testar esse modelo foi descritivo, utilizando-se como técnica para coleta de dados a survey. O objeto de estudo escolhido foi o do setor metal-mecânico do Rio Grande do Sul. Três dos resultados obtidos são os seguintes: (1) a relação entre as capacidades essenciais (tecnológica e transacional) e os ativos específicos é positiva e elevada, o que indica a grande ligação entre esses dois construtos; (2) a relação entre os ativos específicos e o desempenho da firma é maior do que a relação entre as capacidades essenciais e os ativos específicos; (3) a relação da combinação das capacidades essenciais e dos ativos específicos com o desempenho da firma é maior do que a relação entre o desempenho da firma e algum destes construtos, quando estas relações são analisadas de maneira isolada. As implicações teóricas desses resultados confirmam que a firma tem uma natureza tecnológico-transacional. Além disso, os estudos a respeito do desempenho da firma não mais deveriam dedicar-se somente a analisar suas capacidades; antes, deveriam abranger os ativos específicos, como elemento complementar. Finalmente, o fato de confirmar a existência de uma capacidade transacional como elemento-chave da natureza da firma abre uma nova possibilidade para se avançar rumo ao que, nesta tese, se denomina: Paradigma transacional. / A firm is a complex economic agent. This agent has been studied through different theories of the firm. While, some works underlined its technological nature, other works emphasized its transactional nature. However, the nature of the firm covers both dimensions. These two dimensions could be studied through two essential capabilities: the technological one and the transactional one. The objective of this thesis is to analyze the relation between the technological capability and the transactional capability, aiming to generate the assets specificity in order to reach firm’s superior performance compared to its competitors. For accomplishing that objective, it was elaborated a theoretical model based in four theoretical assumptions: capabilities heterogeneity, the existence of a transactional trajectory, besides the technological trajectory; the capabilities are not negotiable; and the capabilities are antecedents to the assets specificity. The model is also composed for four construction blocks: the technological capability, the transactional capability; the specific assets; and the performance. The method employed to test this model was descriptive, utilizing for its operability a survey. The chosen study objet was the Brazilian metal-mechanical sector. Three of the obtained results are the following ones: (1) A relation between the essential capabilities (technological and transactional) and the assets specificity is positive and high, indicating a big link between this two constructs; (2) The relation between the assets specificity and the firm performance is minor than the relation between the capabilities and the assets specificity; (3) a combinational relation of the essential capabilities and the assets specificity with the firm performance is bigger than the relation between the firm performance and some of these construction blocks, when these relations are analyzed in an isolated way. The theoretical implications of those results confirm that the firm has a technological-transactional nature. Furthermore, the studies related to the firm performance should not be devoted anymore just to analyze its capabilities; although, they should cover the assets specificity, as a complementary element. Finally, the fact of confirming the existence of a translational capability as a key element of the nature of the firm opens a new possibility for moving towards of what in this thesis is named as: Transactional paradigm.