23-08-2012, 12:08 PM
GridTP Services for Grid Transaction Processing
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Abstract.
We propose a new service-oriented Grid Transaction Processing ar-chitecture called GridTP based on the OGSA platform and the X/Open DTP model. GridTP services provide a consistent and effective way of making exist-ing, autonomously managed databases available within Grid environments. In the Data Virtualization Services layer, Grid applications, via the WSDL-style TX portType, delineate global transaction boundaries among virtual organiza-tions. In the Common Resource Model layer, GridTP services, via the X/Open-defined interface XA between Database Managers and the Transaction Man-ager, manager local transactions in heterogeneous databases. Therefore, GridTP has made a seamless mechanism for embedding the X/Open DTP model in Grid services to support Grid Transaction Processing, which provides one promising reference implementation for the future Grid Data Services.
Introduction
In Grid environments, the dynamic, distributed, and scalable data access and man-agement will play a significant role in e-science and e-business applications. Existing databases do not provide Grid integration but the development of a new Grid data-base management system is not realistic. However, there exists a standard model for distributed transaction processing called X/Open Distributed Transaction Processing (DTP) [2]. The X/Open DTP model is a standard for distributed transaction process-ing software in which shared resources are located at different sites on a network. The major RDBMS (e.g., ORACLE, Sybase, etc.) support this model by providing the XA interface. Meanwhile, many transaction/message processing middleware (e.g., CICS, Encina, Tuxedo, IBM MQ Services, etc.) conform to X/Open DTP. So it is very at-tracting to integrate the X/Open DTP model into Grid computing.
The Common Resource Model Layer
In the X/Open DTP model, RM (Resource Managers) denotes a shared, recoverable resource such as RDBMS. Because the term Resource Managers in Grid presents a more general concept of resource management (e.g., CPUs, Disks, Network adaptors, etc.), we use the term Database Managers (DMs) to denote the meaning of RM in the
X/Open DTP model. DMs represent manageable data resource such as RDBMS, XML databases, and object databases. All DMs should provide the XA interface for the coordination of distributed transactions. This requirement is easy to be satisfied by many popular RDBMS such as ORACLE, Sybase, DB2.
It is obvious that TM and DMs make a database become the manageable resource, which conforms to Common Resource Models (CRM) in OGSA [3]. According to CRM, the architecture of TM-DMs makes it possible to expose database resource as Grid services in OGSA, which is applicable for OGSI to communicate and manager heterogeneous database resources. The standard XA interface provides the capabili-ties of distributed transaction management. In a word, in the CRM layer, we imple-ment two basic functions: (1) transparent data access operations via the DM-specific API; and (2) the coordination of distributed transaction through the XA interface.
The OGSA Platform Layer
In this layer, OGSI defines fundamental mechanisms such as creation, naming and management on which the OGSA Platform is constructed. These interfaces also in-clude data management, resource management, and transactions. However, transac-tions are not well defined in the current OGSA platform. Our GridTP services pro-vide a solution for Grid transactions building on the top of the OGSA/OGSI architec-ture.
The Data Virtualization Services Layer
Data Virtualization Services (DVS) provide a variety of interfaces, including data caching, data replication, data access and mechanisms for accessing wide range of data types, including flat files, RDBMS, and streaming media. However, GridTP services as a kind of DVS provide transparent access of “virtual databases” among Virtual Organizations (VOs). Of course, the precondition is that the database should support the XA interface.
The interfaces of GridTP can be divided into three categories: (1) the OGSA inter-faces such as naming and dynamic creation; (2) the distributed transaction interface, namely, the TX interface; and (3) Application-specific interfaces. The second cate-gory is of great importance in GridTP and we discuss this in detail.
Conclusions
This paper has made a preliminary, service-oriented proposal called GridTP to deal with Grid Transaction Processing. It is worth reminding that we just discuss how to integrate the traditional X/Open DTP model into Grid services. But the two-phase commit protocol adopted by GridTP is a bit too strict in general for Grid style appli-cations. So it is necessary to extend this model to accommodate the wide variety of Grid applications. In the future version of Hong GridTP, we plan to improve it on the following aspects: (1) supporting the standard WS-Transaction; and (2) conforming to the future Grid Data Service Specification [4]. GridTP can act as the Agreement Provider to support WS-Agreement. That is, GridTP can be integrated into Grid Data Services as a reference implementation of Grid Transaction Processing.