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This paper evaluates performance of distributed fault-tolerant computer systems and replicated NoSQL databases and studies the impact of data consistency on performance and throughput on the example of a three-replicated Cassandra cluster. The paper presents results of heavy-load testing (benchmarking) of Cassandra cluster’s read and write performance which replicas were deployed on Amazon EC2 cloud. The presented quantitative results show how different consistency settings affect the performance of a Cassandra cluster under different workloads considering two deployment scenarios: when all cluster replicas are located in the sane data center, and when they are geographically distributed across different data centers (i.e. Amazon availability zones). We propose a new method of minimizing Cassandra response time while ensuring strong data consistency which is based on optimization of consistency settings depending on the current workload and the proportion between read and write operations.

In the conditions of competition and difficult economic situation, domestic thermal power companies face problems of ensuring their own efficient activity. This is significantly due to the low motivation of the company staff and its productivity. Therefore, an important direction for improving the performance of such businesses will be to create an effective system of direct material incentives for employees, especially with regard to optional bonuses or targeted bonuses based on the use of the KPI. The study is aimed at the development of a strategic personnel management system according to goals based on key performance indicators. The article proposes an approach to developing a Management by Objects (MBO) system based on absolute and relative numerical indicators of the Key Performance Indicators (KPI) performance of the organization as a whole and the decomposition of goals at the level of individual business processes and functional responsibilities of the units. Methodology: In the course of the research general, scientific, theoretical and empirical methods were used, among which are the following: analysis and generalization of literature on the research topic, methods of observation and comparison, structural methods, methods of coordination and formalization, graphical and tabular representation of data. The theoretical and practical database of the strategic personnel management system according to goals is considered as an information base of the research. The scientific significance of the work is that the issue of developing such a system for a municipal enterprise is covered, whose activity depends on the regulatory policy of the state. The role of key performance indicators of KPI is determined as an effective tool in the system of direct material incentives, which assesses the efficiency and effectiveness of business processes, actions and functions of management, specific production, technological and other activities. The reasons that makes it impossible to use KPI without a comprehensive program for improving the personnel management system are analyzed and identified. The practical significance of the results of the study is that a detailed step-by-step scheme for improving the personnel management system is proposed, which will enable the development and implementation of the KPI system to be developed. The use of KPI in the strategic personnel management system will allow the manager to better control the processes of operating activities, create real indicators of the implementation of the enterprise strategy and improve productivity. JEL Classification: А13, D20, L10, M12.

The problem of information security in wireless sensor networks is considered in this paper. An analysis of existing recommendations for information security in wireless sensor networks. It was found that one of the key problems of information security is the hardware limitations of the sensor nodes of the network. It is substantiated that the use of more complex cryptographic protection mechanisms will increase the load on the network. Safety requirements and their description are given. The main groups and types of information security threats in wireless sensor networks are considered. The classification of attacks and protection of wireless sensor networks according to the OSI model is presented. The existing solutions for information security are considered and analyzed. The shortcomings and vulnerabilities of the considered solutions are revealed. The method of public key cryptography is considered, the main advantages and disadvantages of this method are revealed. The analysis and comparison of ECC and RSA encryption methods are carried out. It is substantiated that the use of ECC in wireless sensor networks is more efficient than RSA. The method of cryptography with a symmetric key is considered, the main advantages and disadvantages of this method are indicated. It was found that cryptographic methods using a symmetric key are more priority for use in wireless sensor networks. Cryptographic key management protocols in wireless sensor networks are considered. The classification of key management protocols is given. Secure routing protocols are considered. The classification of secure routing protocols is given. Methods of secure data aggregation are considered. Contradictions between the requirements for confidentiality and data aggregation have been revealed. The method of intrusion detection is considered, the main advantages and disadvantages of this method are revealed. The results of this work should be used in the design of wireless sensor networks.

This paper examines fundamental trade-offs in fault-tolerant distributed systems and replicated databases built over the Internet. We discuss interplays between consistency, availability, and latency which are in the very nature of globally distributed computer systems and also analyse their interconnection with durability and energy efficiency. In this paper we put forward an idea that consistency, availability, latency, durability and other properties need to be viewed as more continuous than binary in contrast to the well-known CAP/PACELC theorems. We compare different consistency models and highlight the role of the application timeout, replication factor and other settings that essentially determine the interplay between above properties. Our findings may be of interest to software engineers and system architects who develop Internet-scale distributed computer systems and cloud solutions.