Schema architecture and their relationships to transaction processing in distributed database systems

We discuss the different types of schema architectures which could be supported by distributed database systems, making a clear distinction between logical, physical, and federated distribution. We elaborate on the additional mapping information required in architecture based on logical distribution in order to support retrieval as well as update operations. We illustrate the problems in schema integration and data integration in multidatabase systems and discuss their impact on query processing. Finally, we discuss different issues relevant to the cooperation (or noncooperation) of local database systems in a heterogeneous multidatabase system and their relationship to the schema architecture and transaction processing

Safe Locking Policies for Dynamic Databases

AbstractYannakakis showed that a locking policy is not safe if and only if it allows a canonical nonserializable schedule of transactions in which all transactions except one are executed serially (Yannakakis, 1982). In the present paper, we study the generalization of this result to a dynamic database, that is, a database that may undergo insertions and deletions of entities. We illustrate the utility of this generalization by applying it to obtain correctness proofs of three locking policies that handle dynamic databases

Concurrency Control in Advanced Database Applications

Concurrency control has been thoroughly studied in the context of traditional database applications such as banking and airline reservations systems. There are relatively few studies, however, that address the concurrency control issues of advanced database applications such as CAD/CAM and software development environments. The concurrency control requirements in such applications are different from those in conventional database applications; in particular, there is a need to support non-serializable cooperation among users whose transactions are long-lived and interactive, and to integrate concurrency control mechanisms with version and configuration control. This paper outlines the characteristics of data and operations in some advanced database applications, discusses their concurrency control requirements, and surveys the mechanisms proposed to address these requirements

The Cord Approach to Extensible Concurrency Control

Database management systems (DBMSs) have been increasingly used for advanced application domains, such as software development environments, workflow management systems, computer-aided design and manufacturing, and managed healthcare. In these domains, the standard correctness model of serializability is often too restrictive. The authors introduce the notion of a concurrency control language (CCL) that allows a database application designer to specify concurrency control policies to tailor the behavior of a transaction manager. A well-crafted set of policies defines an extended transaction model. The necessary semantic information required by the CCL run-time engine is extracted from a task manager, a (logical) module by definition included in all advanced applications. This module stores task models that encode the semantic information about the transactions submitted to the DBMS. They have designed a rule-based CCL, called CORD, and have implemented a run-time engine that can be hooked to a conventional transaction manager to implement the sophisticated concurrency control required by advanced database applications. They present an architecture for systems based on CORD and describe how they integrated the CORD engine with the Exodus Storage Manager to implement altruistic locking

Concurrency Control in Advanced Database Applications

Concurrency control has been thoroughly studied in the context of traditional database applications such as banking and airline reservations systems. There are relatively few studies, however, that address the concurrency control issues of advanced database applications such as CAD/CAM and software development environments. The concurrency control requirements in such applications are different from those in conventional database applications; in particular, there is a need to support non-serializable cooperation among users whose transactions are long-lived and interactive, and to integrate concurrency control mechanisms with version and configuration control. This paper outlines the characteristics of data and operations in some advanced database applications, discusses their concurrency control requirements, and surveys the mechanisms proposed to address these requirements

Supporting Altruistic Protocol in Multidatabase System

Computer Science

A Survey of Traditional and Practical Concurrency Control in Relational Database Management Systems

Traditionally, database theory has focused on concepts such as atomicity and serializability, asserting that concurrent transaction management must enable correctness above all else. Textbooks and academic journals detail a vision of unbounded rationality, where reduced throughput because of concurrency protocols is not of tremendous concern. This thesis seeks to survey the traditional basis for concurrency in relational database management systems and contrast that with actual practice. SQL-92, the current standard for concurrency in relational database management systems has defined isolation, or allowable concurrency levels, and these are examined. Some ways in which DB2, a popular database, interprets these levels and finesses extra concurrency through performance enhancement are detailed. SQL-92 standardizes de facto relational database management systems features. Given this and a superabundance of articles in professional journals detailing steps for fine-tuning transaction concurrency, the expansion of performance tuning seems bright, even at the expense of serializabilty. Are the practical changes wrought by non-academic professionals killing traditional database concurrency ideals? Not really. Reasoned changes for performance gains advocate compromise, using complex concurrency controls when necessary for the job at hand and relaxing standards otherwise. The idea of relational database management systems is only twenty years old, and standards are still evolving. Is there still an interplay between tradition and practice? Of course. Current practice uses tradition pragmatically, not idealistically. Academic ideas help drive the systems available for use, and perhaps current practice now will help academic ideas define concurrency control concepts for relational database management systems

Concurrency Control in Rule-Based Software Development Environments

This dissertation investigates the concurrency control problem in software development environments (SDEs). The problem arises when multiple developers perform activities that concurrently access the project's components, stored as database objects. The interleaved execution of the developers' activities leads to interference if they access overlapping sets of objects concurrently. An SDE can ensure that activities never interfere by modeling their execution in terms of atomic transactions and allowing only serializable schedules. This prevents cooperation, which requires some degree of interference between the activities of multiple developers. To allow cooperation, an SDE must be provided with semantic information about development activities. In rule-based SDEs, the necessary information is readily available in the set of rules that defines the process model of a project. The rules are loaded into the SDE, which provides process-specific assistance through a rule chaining engine. A single user command might lead the chaining engine to initiate a rule chain. The concurrency control problem in rule-based SDEs manifests itself in terms of interference between concurrent rule chains. We present a mechanism that extracts semantic information from the process model to solve the concurrency control problem without obstructing cooperation. The mechanism is composed of two modules: (1) a conflict detection module, which models activities as nested transactions and uses two-phase locking to detect interference; and (2) a conflict resolution module, which employs two protocols to resolve interference. The first protocol, seep, uses the process model to implement a priority-based scheme that aborts the "least important" of the interfering transactions. The second protocol, peep, overrides SCCP by consulting process-specific control rules, written by the project administration. Each control rule describes a specific interference and the actions that resolve it. We have implemented SCCP and parts ofPCCP in MARVEL, a multi-user rule-based SDE developed at Columbia

Synchronization of Multiple Agents in Rule-Based Development Environments

The Rule-Based Development Environment (RBDE) is recently-developed approach for providing intelligent assistance to developers working on a large-scale software projects. RBDEs model the development process in terms of rules, and then enact this model by automatically firing rules at the appropriate time. The RBDE approach has been used to develop single-user environment, but support for multiple developers cooperating on the same project is still not available because of the lack of mechanisms that can synchronize the efforts of multiple developers, who concurrently select commands, causing the firing of multiple rules (either directly or via chaining) that concurrently access shared data. Conflicts between different rules and concurrent .access to shared data may cause the violation of consistency in the project database, and thus necessitate the synchronization of concurrent activities. The conjecture of this proposal is that an RBDE can provide the required synchronization if it is provided with knowledge about what it means for the data of a specific project to be in a consistent state, and about the semantics of operations that developers perform on the data. The research that this paper proposes will formulate a frame work for specifying consistency of data in an RBDE, and formulate a mechanism for synchronizing the actions of concurrent rules fired on behalf of multiple developers cooperating on a common or different tasks

Oze: Decentralized Graph-based Concurrency Control for Real-world Long Transactions on BoM Benchmark

In this paper, we propose Oze, a new concurrency control protocol that handles heterogeneous workloads which include long-running update transactions. Oze explores a large scheduling space using a fully precise multi-version serialization graph to reduce false positives. Oze manages the graph in a decentralized manner to exploit many cores in modern servers. We also propose a new OLTP benchmark, BoMB (Bill of Materials Benchmark), based on a use case in an actual manufacturing company. BoMB consists of one long-running update transaction and five short transactions that conflict with each other. Experiments using BoMB show that Oze keeps the abort rate of the long-running update transaction at zero while reaching up to 1.7 Mtpm for short transactions with near linear scalability, whereas state-of-the-art protocols cannot commit the long transaction or experience performance degradation in short transaction throughput