Transactional memory (TM) simplifies parallel programming by guaranteeing that transactions appear to execute atomically and in isolation. Implementing these properties includes providing data version management for the simultaneous storage of both new (visible if the transaction commits) and old (retained if the transaction aborts) values. Most (hardware) TM systems leave old values "in place" (the target memory address) and buffer new values elsewhere until commit. This makes aborts fast, but penalizes (the much more frequent) commits. In this paper, we present a new implementation of transactional memory, log-based transactional memory (LogTM), that makes commits fast by storing old values to a per-thread log in cacheable virtual memory and storing new values in place. LogTM makes two additional contributions. First, LogTM extends a MOESI directory protocol to enable both fast conflict detection on evicted blocks and fast commit (using lazy cleanup). Second, LogTM handles aborts in (library) software with little performance penalty. Evaluations running micro- and SPLASH-2 benchmarks on a 32-way multiprocessor support our decision to optimize for commit by showing that only 1-2% of transactions abort.

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LogTM: log-based transactional memory

Transactional Information Systems is the long-awaited, comprehensive work from leading scientists in the transaction processing field. Weikum and Vossen begin with a broad look at the role of transactional technology in today's economic and scientific endeavors, then delve into critical issues faced by all practitioners, presenting today's most effective techniques for controlling concurrent access by multiple clients, recovering from system failures, and coordinating distributed transactions.


The authors emphasize formal models that are easily applied across fields, that promise to remain valid as current technologies evolve, and that lend themselves to generalization and extension in the development of new classes of network-centric, functionally rich applications. This book's purpose and achievement is the presentation of the foundations of transactional systems as well as the practical aspects of the field what will help you meet today's challenges.

* Provides the most advanced coverage of the topic available anywhere--along with the database background required for you to make full use of this material.
* Explores transaction processing both generically as a broadly applicable set of information technology practices and specifically as a group of techniques for meeting the goals of your enterprise.
* Contains information essential to developers of Web-based e-Commerce functionality--and a wide range of more "traditional" applications.
* Details the algorithms underlying core transaction processing functionality.

Table of Contents

PART ONE - BACKGROUND AND MOTIVATION
Chapter 1 What Is It All About?
Chapter 2 Computational Models
PART TWO - CONCURRENCY CONTROL
Chapter 3 Concurrency Control: Notions of Correctness for the Page Model
Chapter 4 Concurrency Control Algorithms
Chapter 5 Multiversion Concurrency Control
Chapter 6 Concurrency Control on Objects: Notions of Correctness
Chapter 7 Concurrency Control Algorithms on Objects
Chapter 8 Concurrency Control on Relational Databases
Chapter 9 Concurrency Control on Search Structures
Chapter 10 Implementation and Pragmatic Issues
PART THREE - RECOVERY
Chapter 11 Transaction Recovery 
Chapter 12 Crash Recovery: Notion of Correctness
Chapter 13 Page Model Crash Recovery Algorithms
Chapter 14 Object Model Crash Recovery
Chapter 15 Special Issues of Recovery
Chapter 16 Media Recovery
Chapter 17 Application Recovery
PART FOUR - COORDINATION OF DISTRIBUTED TRANSACTIONS
Chapter 18 Distributed Concurrency Control
Chapter 19 Distributed Transaction Recovery
PART FIVE - APPLICATIONS AND FUTURE PERSPECTIVES
Chapter 20 What Is Next?

Transactional Information Systems: Theory, Algorithms, and the Practice of Concurrency Control and Recovery

A multidatabase system (MDBS) is a facility that allows users access to data located in multiple autonomous database management systems (DBMSs). In such a system, global transactions are executed under the control of the MDBS. Independently, local transactions are executed under the control of the local DBMSs. Each local DBMS integrated by the MDBS may employ a different transaction management scheme. In addition, each local DBMS has complete control over all transactions (global and local) executing at its site, including the ability to abort at any point any of the transactions executing at its site. Typically, no design or internal DBMS structure changes are allowed in order to accommodate the MDBS. Furthermore, the local DBMSs may not be aware of each other and, as a consequence, cannot coordinate their actions. Thus, traditional techniques for ensuring transaction atomicity and consistency in homogeneous distributed database systems may not be appropriate for an MDBS environment. The objective of this article is to provide a brief review of the most current work in the area of multidatabase transaction management. We first define the problem and argue that the multidatabase research will become increasingly important in the coming years. We then outline basic research issues in multidatabase transaction management and review recent results in the area. We conclude with a discussion of open problems and practical implications of this research.

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Overview of multidatabase transaction management

This paper proposes a hardware transactional memory (HTM) system called LogTM Signature Edition (LogTM-SE). LogTM-SE uses signatures to summarize a transactions read-and write-sets and detects conflicts on coherence requests (eager conflict detection). Transactions update memory "in place" after saving the old value in a per-thread memory log (eager version management). Finally, a transaction commits locally by clearing its signature, resetting the log pointer, etc., while aborts must undo the log. LogTM-SE achieves two key benefits. First, signatures and logs can be implemented without changes to highly-optimized cache arrays because LogTM-SE never moves cached data, changes a blocks cache state, or flash clears bits in the cache. Second, transactions are more easily virtualized because signatures and logs are software accessible, allowing the operating system and runtime to save and restore this state. In particular, LogTM-SE allows cache victimization, unbounded nesting (both open and closed), thread context switching and migration, and paging

/pdf/logtm-se-decoupling-hardware-transactional-memory-from-1z2dmi6kbn.pdf

LogTM-SE: Decoupling Hardware Transactional Memory from Caches

Fault tolerance is a key requirement in process support systems (PSS), a class of distributed computing middleware encompassing applications such as workflow management systems and process centered software engineering environments. A PSS controls the flow of work between programs and users in networked environments based on a "metaprogram" (the process). The resulting applications are characterized by a high degree of distribution and a high degree of heterogeneity (properties that make fault tolerance both highly desirable and difficult to achieve). We present a solution for implementing more reliable processes by using exception handling, as it is used in programming languages, and atomicity, as it is known from the transaction concept in database management systems. We describe the mechanism incorporating both transactions and exceptions and present a validation technique allowing to assess the correctness of process specifications.

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Exception handling in workflow management systems

Concepts and applications of multilevel transactions and open nested transactions

A federated database management system (FDBMS) is a special type of distributed database system that enables existing local databases, in a heterogeneous environment, to maintain a high degree of autonomy. One of the key problems in this setting is the coexistence of local transactions and global transactions, where the latter access and manipulate data of multiple local databases. In modeling FDBMS transaction executions the authors propose a more realistic model than the traditional read/write model; in their model a local database exports high-level operations which are the only operations distributed global transactions can execute to access data in the shared local databases. Such restrictions are not unusual in practice as, for example, no airline or bank would ever permit foreign users to execute ad hoc queries against their databases for fear of compromising autonomy. The proposed architecture can be elegantly modeled using the multilevel nested transaction model for which a sound theoretical foundation exists to prove concurrent executions correct. A multilevel scheduler that is able to exploit the semantics of exported operations can significantly increase concurrency by ignoring pseudo conflicts. A practical scheduling mechanism for FDBMSs is described that offers the potential for greater performance and more flexibility than previous approaches based on the read/write model. >

Semantics-based multilevel transaction management in federated systems

Transaction management in shared databases is generally viewed as a combination of two problems, concurrency control and recovery, which have been considered as orthogonal problems. Consequently, the correctness criteria derived for these problems are incomparable. Recently a unified theory of concurrency control and recovery has been introduced that is based on commutativity and performs transaction recovery by submitting inverse operations for operations of aborted transactions. In this paper we provide a constructive correctness criterion that leads to the design of unified protocols that guarantee atomicity and serializability.

Unifying concurrency control and recovery of transactions

Multi-level transactions and open nested transactions

The 2PC (two-phase commit) protocol together with strict 2PL (two-phase locking) can be considered as a de-facto standard for distributed transaction processing. However, 2PC is often unacceptable from a performance and execution-autonomy point of view. Multilevel transaction management offers an alternative solution that allows early commits of subtransactions and thus improves performance and execution autonomy. While the theory of this approach is well established, a practical evaluation in a multi-database environment is still lacking. This paper describes a prototype implementation and initial measurements that compare transaction processing with 2PC versus distributed multi-level transaction management. Although we used SQL in our examples, the concepts presented are applicable to any notion of distributed object management system. >

H.-J. Schek

Papers

Concepts and applications of multilevel transactions and open nested transactions

Semantics-based multilevel transaction management in federated systems

Unifying concurrency control and recovery of transactions

Multi-level transactions and open nested transactions

Implementation and performance of multi-level transaction management in a multidatabase environment