Data replication is an increasingly important topic as databases are more and more deployed over clusters of workstations. One of the challenges in database replication is to introduce replication without severely affecting performance. Because of this difficulty, current database products use lazy replication, which is very efficient but can compromise consistency. As an alternative, eager replication guarantees consistency but most existing protocols have a prohibitive cost. In order to clarify the current state of the art and open up new avenues for research, this paper analyses existing eager techniques using three key parameters. In our analysis, we distinguish eight classes of eager replication protocols and, for each category, discuss its requirements, capabilities, and cost. The contribution lies in showing when eager replication is feasible and in spelling out the different aspects a database replication protocol must account for.

Thii paper describes the techniques used to optimize relational queries in the SDD-1 distributed database system. Queries are submitted to SDD-1 in a high-level procedural language called Datalan-guage. Optimization begins by translating each Datalanguage query into a relational calculus form called an envelope, which is essentially an aggregate-free QUEL query. This paper is primarily concerned with the optimization of envelopes. Envelopes are processed in two phases. The first phase executes relational operations at various sites of the distributed database in order to delimit a subset of the database that contains all data relevant to the envelope. This subset is called a reduction of the database. The second phase transmits the reduction to one designated site, and the query is executed locally at that site. The critical optimization problem is to perform the reduction phase efficiently. Success depends on designing a good repertoire of operators to use during this phase, and an effective algorithm for deciding which of these operators to use in processing a given envelope against a given database. The principal reduction operator that we employ is called a

The widespread use of clusters and web farms has increased the importance of data replication. In this paper, we show how to implement consistent and scalable data replication at the middleware level. We do this by combining transactional concurrency control with group communication primitives. The paper presents different replication protocols, argues their correctness, describes their implementation as part of a generic middleware tool, and proves their feasibility with an extensive performance evaluation. The solution proposed is well suited for a variety of applications including web farms and distributed object platforms.

In previous papers [SC05, SBC+07], some of us predicted the end of “one size fits all ” as a commercial relational DBMS paradigm. These papers presented reasons and experimental evidence that showed that the major RDBMS vendors can be outperformed by 1-2 orders of magnitude by specialized engines in the data warehouse, stream processing, text, and scientific database markets. Assuming that specialized engines dominate these markets over time, the current relational DBMS code lines will be left with the business data processing (OLTP) market and hybrid markets where more than one kind of capability is required. In this paper we show that current RDBMSs can be beaten by nearly two orders of magnitude in the OLTP market as well. The experimental evidence comes from comparing a new OLTP prototype, H-Store, which we have built at M.I.T. to a popular RDBMS on the standard transactional benchmark, TPC-C. We conclude that the current RDBMS code lines, while attempting to be a “one size fits all ” solution, in fact, excel at nothing. Hence, they are 25 year old legacy code lines that should be retired in favor of a collection of “from scratch ” specialized engines. The DBMS vendors (and the research community) should start with a clean sheet of paper and design systems for tomorrow’s requirements, not continue to push code lines and architectures designed for yesterday’s needs. 1.

This paper presents in detail an efficient and provably correct algorithm for database replication over partitionable networks. Our algorithm avoids the need for end-toend acknowledgments for each action while supporting network partitions and merges and allowing dynamic instantiation of new replicas. One round of end-to-end acknowledgments is required only upon a membership change event such as a network partition. New actions may be introduced to the system at any point, not only while in a primary component. We show how performance can be further improved for applications that allow relaxation of consistency requirements. We provide experimental results that demonstrate the efficiency of our approach.

data types are programming language constructs that encapsulate the representations of a set of objects and a set of operations on these objects. The operations are the only means of accessing and manipulating the objects. From the perspective of transaction processing, ADTs introduce a need to deal with abstract operations. The operations of transactions that execute on ADTs are not simple reads and writes, but are more abstract, such 5.2 Transaction Schemes 13 Transaction Structure simple objects instances of ADTs complex objects flat transactions closed nesting open nesting combinations active objects [DAYA88] [STON90] [BADR88] [WEIH88] [HERL90] [ESWA75] [BERN87] [MOSS85] [GARC87] [GARC90] DOM [ELMA90] [PU88] [FEKE89] [BANC85] [KOTZ88] [FARR89] Object Structure FIGURE 5.2 Representation of transaction model space and examples. The labels for the references are given following each citation in the Bibliography. 14 Chapter 5. Transaction Model for Distributed Object Systems as Ins...

We present a new architecture and algorithm for distributed replicated database systems. The replication algorithm operates in the presence of message omission faults, processor crashes and recoveries, and network partitions and remerges. The architecture exploits a group communication service to minimize communication costs and to eliminate forced disk writes in the critical path, while preserving complete and consistent operation. End-to-end agreement is required only after a change in the membership of the connected servers, rather than on a per action basis. The updates are globally ordered and, if the system has partitioned, they are applied to the database when they become known to the primary component of the partitioned system. An application may, however, read data and initiate updates at any time, even in a component that is not the primary component. This approach renders replication more efficient and more scalable and, therefore, applicable to many more systems.

... this article, we analyze several quorum types in order to better understand their behavior in practice. The results obtained challenge many of the assumptions behind quorum based replication. Our evaluation indicates that the conventional read-one/write-all-available approach is the best choice for a large range of applications requiring data replication. We believe this is an important result for anybody developing code for computing clusters as the read-one/write-all-available strategy is much simpler to implement and more flexible than quorum-based approaches. In this article, we show that, in addition, it is also the best choice using a number of other selection criteria

. This paper presents a typical replicated application in a distributed system. The application was developed on top of Transis, a reliable and efficient transport layer protocol. The basic properties of the protocol and the advantages of using Transis as the transport layer are discussed. The algorithms used in this application can lead to better solutions in the area of distributed transaction systems and replicated databases. 1 Introduction The reliability and availability of loosely coupled distributed systems is becoming a requirement for many computer systems. One of the main infrastructure services is a distributed database. This paper addresses some aspects of information dissemination within such a service in a dynamic loosely coupled environment. We chose to tackle this complex problem by studying a particular application. The application we focus on is a Replicated Mail Service. In our design of this service, the database of messages is replicated among several mail servers...

Chopping transactions into pieces is good for performance but may lead to non-serializable executions. Many researchers have reacted to this fact by either inventing new concurrency control mechanisms, weakening serializability, or both. We adopt a different approach. We assume a user who -- has access only to user-level tools such as (i) choosing between degree 2 and degree 3 isolation levels (degree 2 corresponds to level 1 in the new ANSI SQL terminology) (ii) the ability to execute a portion of a transaction using multiversion read consistency, and (iii) the ability to reorder the instructions in transaction programs; and -- knows the set of transactions that may run during a certain interval (users are likely to have such knowledge for online or real-time transactional applications).