INTERNATIONAL JOURNAL OF NATURAL AND APPLIED SCIENCES (IJNAS), VOL. 6, NOS.1& 2 (2011); P. 63 – 71, 1TABLE, . Issues on concurrency controls in transactional database system: The automatic teller machine (ATM) problem. F. U. Ogban 1* and P. Asagba 2 INTRODUCTION Concurrent computing is a form of computing in which programs are designed as collections of interacting computational processes that may be executed in parallel (Taubenfeld, 2006). Concurrent programs can be executed sequentially on a single processor by interleaving the execution steps of each computational process, or executed in parallel by assigning each computational process to one of a set of processors that may be close or distributed across a network (Ben-Ari, 2006). Above understanding if considered strictly, would limit our avenues for implementing concurrent computing in some instance. It must be noted that the main challenges in designing concurrent programs are ensuring the correct sequencing of the interactions or communications between different computational processes, and coordinating access to resources that are shared among processes. In such design, especially in transactional computing, where database contents are read and written, our target is to avoid interferences of a process (with its associated data) and other processes (with its own associated data). A number of different methods can be used to implement concurrent programs, such as implementing each computational process as an operating system process. (Brinch, 1993, Hoare, 1974) or implementing the computational processes as a set of threads within a single operating system process (Taubenfeld; 2006). The concept of nested transactions offers more decomposable execution units and finer-grained control over concurrency and recovery than "flat" transactions. Furthermore, it supports the decomposition of a "unit of work" into subtasks and their appropriate distribution in a computer system as a prerequisite of intra-transaction parallelism. However, to exploit its full potential, suitable granules of concurrency control as well as access modes for shared data are necessary (Ben-Ari, 2006). In this paper, we investigate various issues of concurrency control for nested transactions. Communication in concurrent computing In some concurrent computing systems, communication between the concurrent components is hidden from the programmer (e.g., by using futures), while in others it must be handled explicitly. Explicit communication can be divided into two classes as fellows a).Shared memory communication: Concurrent components communicate by altering the contents of shared memory locations (exemplified by Java and C#). This style of concurrent programming usually requires the application of some form of locking (e.g., mutexes (means mutual exclusion), semaphores, or monitors) to coordinate between threads. b). Message passing communication: Concurrent components communicate by exchanging messages (exemplified by Erlang and occam). The exchange of messages may be carried out asynchronously (sometimes referred to as "send and pray", although it is standard practice to resend messages that are not ABSTRACT Concurrency control issues like the “isle-of-March” has come but not gone. It is not surprising that several models designed to handle concurrency control in databases; there still exist some overheads in transactional database controls. One of such problems is the incompletion of the execution of necessary codes within the critical region of a lock transaction implementation thus generating data integrity fault (–such as dirty read, non-repeated read and phantom read) and inconsistent data (- such as non-submitted data, late submitted data etc). In this work, the locks paradigms were reappraised to suit situations of usage and recommend particular areas of application of the different locking strategies so designed. New construct of control issues were recreated vis-à-vis the application situation found on ground like the Automatic Teller Machine problem. *Corresponding author. Email: 1 Department of Mathematics/Statistics & Computer Science, University of Calabar, Calabar, Nigeria 2 Department of Computer Science, University of Port Harcourt, Port Harcourt, Nigeria © 2011 International Journal of Natural and Applied Sciences (IJNAS). All rights reserved. 63