Gasov

 The authors propose an approach to estimation of time characteristics of query execution to a parallel database system (PDBS). A model of query execution to PDBS with a p F(R) plan as a closed-loop queue system was developed. It was shown that the model could be reduced to a “repairman” model if there was a bottleneck. The possibility of reducing this model to an open-loop queue system is proved. Parameters of this model are determined. A policy of calculation of performance indexes of PDBS built on any architecture (SE, SD, SN) is formulated.

This article deals with the analysis of approaches to the formation of password system for protection of LAN server when connecting user network. Based on the demands of information security, main functions of password system for protection of server were identified. Set of main components of password system was determined; it consisted of length of password, password’s alphabet, password’s expiration date, unicity of password and variants of password’s blocking modes. Analytical expression for evaluating the required length of password, which guaranteed the certain given level of probability of guessing password considering speed and time of guessing, and also the alphabet of password, was presented in the article. In order to provide the required level of information security, practical recommendations on the formation of password system for protection of LAN server when connecting user network were given.

Known architectures of parallel database systems are analyzed in this article. The authors also consider expressions for evaluating the mean time of connection of two tables by NLJ and HJ methods; relevant mathematical expectations for SE, SD, SN architectures of parallel database systems are also considered. The authors provide examples of query processing in the following resources: disk array, RAM, connecting bus and processor. If there is a bottleneck in the resource, processing in that resource can be simulated by using the M/M/1 queue system. Parameters of that queue system are evaluated. The example of calculation which allowed to make several non-trivial conclusions is considered in the article.