This paper describes the implementations of mirroring technology of the selected database systems – Microsoft
SQL Server, MySQL and Caché. By simulating critical failures the systems behavior and their resilience against failure
were tested. The aim was to determine whether the database mirroring is suitable to use in continuous metallurgical
processes for ensuring the fault-tolerant solution at affordable cost. The present day database systems are characterized
by high robustness and are resistant to sudden system failure. Database mirroring technologies are reliable
and even low-budget projects can be provided with a decent fault-tolerant solution. The database system
technologies available for low-budget projects are not suitable for use in real-time systems.Web of Science551868

Danel, Roman

Janovská, Kamila

Johanides, David

Kozel, Roman

Otte, Lukáš

Vilamová, Šárka

Řepka, Michal

DSpace at VSB Technical University of Ostrava

83METALURGIJA 55 (2016) 1, 83-86R. DANEL, L. OTTE, R. KOZEL, D. JOHANIDES, Š. VILAMOVÁ, K. JANOVSKÁ, M. ŘEPKA DATABASE MIRRORING IN FAULT-TOLERANT CONTINUOUS TECHNOLOGICAL PROCESS CONTROLReceived – Prispjelo: 2015-02-17Accepted – Prihvaćeno: 2015-07-15Preliminary Note – Prethodno priopćenjeR. Danel, L. Otte, R. Kozel, D. Johanides, Š. Vilamová, M. Řepka, Faculty of Mining and Geology, VŠB–Technical University of Ostrava, Czech RepublicK. Janovská, Business School Ostrava plc., Czech RepublicThis paper describes the implementations of mirroring technology of the selected database systems – Microsoft SQL Server, MySQL and Caché. By simulating critical failures the systems behavior and their resilience against failure were tested. The aim  was to determine whether the database mirroring is suitable to use in continuous metallurgi-cal processes for ensuring the fault-tolerant solution at affordable cost. The present day database systems are char-acterized by high robustness and are resistant to sudden system failure. Database mirroring technologies are reli-able and even low-budget projects can be provided with a decent fault-tolerant solution. The database system technologies available for low-budget projects are not suitable for use in real-time systems.Key words: Continuous production; control; database mirroring; fault-tolerant system INTRODUCTIONIn the case of continuous processes, one of the im-portant requirements is to ensure the robustness of the control system, i.e. deployment of fault-tolerant and disaster recovery solutions. Compared to the recent past, the production management is now increasingly dependent on information (or control) systems, which entails the ever-present emphasis on increasing labour productivity, increasing quality demands of customers, and pressure from the competition. The failure of an in-formation system can have negative consequences both for the process control and for the quality assurance. In continuous process control the collection of data from production operation is fundamental and the data taken from the sensors by sampling represent a time series. Solutions falling into the category of fault-tolerant sys-tems need to ensure continuity of such data.Fault-tolerant solutions of information (or control) systems without the use of Enterprise level technologies are based on the existence of a backup (a secondary copy) of the system which will take over in the event of production system failure. The backup system must not only be an identical copy of the application software but also work with current data. The objective of research was to find solution of a database technology for ensur-ing data continuity at affordable costs. EXAMPLES OF CONTROL OF CONTINUOUS PRODUCTION PROCESS IN METALLURGY The technological processes in metallurgy or coke processing industry operate mostly continuously. This ISSN 0543-5846METABK 55(1) 83-86 (2016)UDC – UDK 669.015.002.2:657.6:338.5=111puts specific demands on the control and information systems providing real time feedback for the production management  [1]. One of the information system tasks is acquiring data representing a time series, which are used for fur-ther calculations (trends, balances, forecasting). In the case of system failure the broken time series data would lose their relevance, therefore it is necessary to make such systems fault-tolerant.An example of the control system, where securing the continuity of time series data is of paramount impor-tance, is a production control system at ArcelorMittal Ostrava steelworks (formerly Nová Huť) – Figure 1. The MES system (Manufacturing Execution Systems) was designed and put into operation by company Real Time Software - R.T.S. cs s.r.o. (1993-present) [2]. It is a comprehensive system consisting of a wide range of modules and components, such as process data collec-tion, dispatch control, technology monitoring, balance calculations, and data transfer to the corporate ERP sys-tem (formerly IBM, nowadays SAP). One of the mod-ules is responsible for controlling the operation cycle of foundry ladles. When operating foundry ladles the tem-perature control is paramount in order to avoid unde-sired cooling-down. If the ladle contains molten metal and the temperature falls below a certain threshold, a stoppage may occur which may cause damage to the ladle. Prior to tapping the foundry ladles are heated to the desired temperature by high-temperature heating. During an operation cycle the foundry ladle goes through the following operating steps: high-temperature heating, tapping, transporting the molten steel, process-ing in ladle furnace, casting, open air cooling (before tapping or after casting the steel) and cooling below the lid. For all of these states of the ladle a mathematical model was constructed to calculate the enthalpy. The 84R. DANEL et al.: DATABASE MIRRORING IN FAULT-TOLERANT CONTINUOUS TECHNOLOGICAL PROCESS... METALURGIJA 55 (2016) 1, 83-86automated control system of the steelworks contains partial technological models monitoring the entire oper-ating cycle of foundry ladles, namely the thermal state of the ladle lining. Based on the analysis of experimen-tal measurements of surface and internal temperatures of the ladle and concurrent measurements of steel tem-perature during all operation steps with a filled ladle, model constants were created for ladle thermal state as-sessment. Enthalpy information available to the dis-patchers describes temperature conditions in the ladle, allowing optimizing the production sequence. The heat-ing time thus can be set to give the ladle sufficient en-thalpy for tapping, and the ladle operation cycle can be optimized so that the ladle heat loss is minimized and at the same time the conditions for operation of alkaline ladle linings are met [3]. The calculation of the ladle enthalpy shows that it is unnecessary to heat the ladle for the whole time while it resides at the high-tempera-ture heating station before the next tapping. To preserve the heat accumulated in the ladle lining it suffices to cover the ladle with a lid as soon as the casting is fin-ished. Thus using the model of the foundry ladle ther-mal state in controlling the high-temperature ladle heat-ing can turn into considerable savings of fuel gas. [4]In order for the enthalpy calculation model to work the information system needs measurement data in the form of continuous time series. It is the critical compo-nent of the information system – if there is a loss of continuity in measurement data because of the database failure the enthalpy calculations cease to provide useful outputs.  RESEARCH OBJECTIVES The aim of the research was to assess the suitability of database mirroring technology when controlling con-tinuous production processes in metallurgy, coke pro-duction or mining. The research was restricted to solu-tions available in Standard category of the database systems. The reason for choosing Standard versions was to find a suitable technology without the necessity of heavy investments.After initial analysis the current versions of the fol-lowing database systems for testing and comparison were selected: Microsoft SQL Server, Oracle, MySQL and Caché.Testing was performed in Microsoft Windows operat-ing system environment. This constraint was introduced because one of the tested database platforms, Microsoft SQL Server, can run only on Windows systems, and also based on the fact that all potential clients in Moravia re-gion in metallurgical or mining industry interested in de-ployment of this technology operate their information systems on the Windows Server platform.Oracle is currently the leader in the database tech-nologies and Oracle systems have been supplied with mirroring technology for many years. MySQL belongs among the most frequently used open-source database systems. Another major open-source platform Post-greSQL was considered but eventually excluded be-cause PostgreSQL system is developed in Linux operat-ing systems environment and its use in Windows sys-tems is possible by porting it via Cygwin emulator. Last database platform included in tests was InterSystems Caché. It is an object-oriented database system with a high-quality database mirroring solution.For database technology testing purposes has been assumed a model of an information system for continu-ous process control. Scheme of the model example of an information system is shown in Figure 2.In this model, the MES information system is con-nected to the “production” network, which can to read Figure 1 Foundry ladle – ArcellorMittal [5]Figure 2  Model example of an information system for continuous process control.  Source: own processing85R. DANEL et al.: DATABASE MIRRORING IN FAULT-TOLERANT CONTINUOUS TECHNOLOGICAL PROCESS...METALURGIJA 55 (2016) 1, 83-86data from the sensors, measuring devices, PLCs, con-trollers, and other elements of process automation [6]. For test purposes it is not important whether sensors are connected by current loops through data concentrator or if a fieldbus (Profibus, Modbus, etc.) and OPC server are used. The information system itself consists of the application server and the database server with a data-base instance labeled as a production database.This instance is then mirrored to the backup data-base server, which is ready to take over the role of the production server in case of its failure. Role take-over can be either initiated by scripts or it is possible to use third server with a database instance in the role of wit-ness (arbiter). Witness then automatically monitors the status of the production server ensures the activation of the backup server in case of failure.RESULTSFor assessment of the database systems there was established the following categories:a) Difficulty of deploying a database mirrorb) Controllability of systems using scriptsc)  Speed of the transition to a mirror after failure (downtime duration)d) Implementation costse) Reliability following crash testsThe Oracle database system was excluded from fur-ther testing at the very beginning. To ensure Disaster Recovery the Oracle database features a variety of tech-nologies: Real Application Cluster, Data Guard or Ora-cle GoldenGate. These technologies, however, are only available in the Enterprise versions of the database and require greater investment in licenses.Certain disadvantages can be noted as well when us-ing the MySQL system. MySQL is publicly synonymous with an open source solution used “for free”, the licens-ing terms, however, clearly define the use of MySQL un-der the GPL license (information system using MySQL must be provided including source code) or you must purchase a license. Another disadvantage is the lack of technology equivalent to mirroring. MySQL does have a mechanism allowing database replication at the transac-tion log level. However, the method of connection and replication activation is different and it is not a trivial op-eration. After synchronization of the databases it is nec-essary to make a backup of the database, do a recovery at the receiving side of replication, and then read the new transactions start position address from the transaction log in order to initiate the replication. Deploying replica-tion in fully automatic mode is quite difficult. Based on the performed testing and feature compar-ison have been reached the following conclusions:1. Microsoft SQL Server and Caché database systems provide comparable functionality at a comparable price, Oracle in comparably priced edition does not support mirroring. MySQL only provides replica-tion that has comparable performance, but is inferior in terms of administration.2. Solutions without a third server in the role of arbiter in case of failure must somehow ensure redirection of clients to the database backup server, Microsoft SQL Server database must be activated from the re-covery mode by a script. 3. Using the third server in the role of arbiter on one hand greatly simplifies work with the system, on the other hand, it comprises another component that must be managed and the solution cost increases. The arbiter, however, can take care of redirecting clients through using virtual IP address without al-tering the configuration. The tests showed that even if the session between production and backup server is managed by the arbiter, a failure leads to some delay, during which data cannot be written in any system, and arbiter in itself does not provide any buffering of data write requirements. This delay de-pends on the system configuration and on the speed of transition of the migrated database to operating mode. The default setting will lead to a data dropout lasting tens of seconds. Within a real-time control, it is necessary to provide buffering of data write re-quirements at application level.4. Crash tests conducted on all database systems con-firmed their high robustness, damage to the database or incorrect behavior was recorded in none of the cases. The performed tests did not prove any data-base system to be significantly better.CONCLUSIONThe aim of the research project was to assess the da-tabase mirroring technology of major database system platforms to provide a low-cost solution. By studying ex-isting information systems in metallurgy or coke industry and analysing the requirements, the model example of an information system for testing has been designed. The results of the testing confirmed that present day database systems are characterized by high robustness and are resistant to sudden system failure. Database mirroring technologies are reliable and even low-budg-et projects can be provided with a decent fault-tolerant solution. Despite the abundance of information sources on the topic, deploying a database mirror is still not a trivial matter and requires extensive experience and re-searching of multiple information sources. The data-base system technologies available for low-budget pro-jects are not suitable for use as real-time systems, in which case it is necessary to complement these tech-nologies by providing software solutions for buffering or to invest in “enterprise” solutions.AcknowledgementThe paper was written in connection with the SGS SP2014/2 project.86R. DANEL et al.: DATABASE MIRRORING IN FAULT-TOLERANT CONTINUOUS TECHNOLOGICAL PROCESS... METALURGIJA 55 (2016) 1, 83-86REFERENCES[1] Š. Vilamová, K. Janovská, R. Kozel, I. Vozňáková, E. Švecová, New Trends in the Management within the Me-tallurgy Firms. Metal 2012: 21st International Conference on Metallurgy and Materials. Ostrava: Tanger, 2012, p. 1897-1903. [2] R.T.S. cs s.r.o. [online] [cit. 2014-12-06]. Athttp://www. rtscs.cz/ index_en.php.[3] P. Tvardek, P. Hašek, D. Jančar, Optimization of the Ther-momechanical Process of the Ladle. Journal Hutnické li-sty, (2008) 5, 14 - 19. [online] [cit. 2014-12-07] At http://www.hutnickelisty.cz/ userdata/pages/5/hl5_2008.pdf.[4] D. Jančar, F. Ovčáčik, P. Tvardek, Využití entalpie vyzdívky licích pánví pro úsporu topného plynu při jejich předehřevu v ocelárně ISPAT Nová Huť a.s. Ostrava. The microCAD 2005 International Scientific Conference, Uni-versity of Miskolc, 2005.[5] Jak se v Ostravě lije ocel [online] [cit. 2014-12-07]. Avai-lable at http://www.ceskatelevize.cz/ ct24/ekonomika/254077-jak-se-dnes-v-ostrave-lije-ocel/[6] H. Meyer, F. Fuchs, K. Thiel, Manufacturing Execution Systems: Optimal Design, Planning and Deployment. New York: McGraw-Hill, c2009,248 p. Note:  The responsible translator for English language is PhDr. Pavel Král - Language services (translation, localisation and teaching), Olomouc, Czech Republic

Database mirroring in fault-tolerant continuous technological process control

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Database mirroring in fault-tolerant continuous technological process control

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