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Topic: Optimistic concurrency control

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	Concurrency control - Wikipedia, the free encyclopedia
		Concurrency control is especially applicable to database management systems, which must ensure that transactions are executed safely and that they follow the ACID rules, as described in the following section.
		In computer science -- in the field of concurrent programming (see also parallel programming and parallel computing on multiprocessor machines) -- concurrency control is a method used to ensure that correct results are generated, while getting those results as quickly as possible.
		All the currently implemented lock-based and almost all the implemented non-lock based concurrency controls will guarantee that the resultant schedule is conflict serializable; however, there are many academic texts encouraging view serializable schedules for environments where gains due to improvement in concurrency outstrip overheads in generating schedule plans.
	en.wikipedia.org /wiki/Concurrency_control (359 words)

	Optimistic concurrency control - Wikipedia, the free encyclopedia
		In computer science, in the field of databases, optimistic concurrency control, (OCC) is a concurrency control method used in relational databases without using locking.
		Optimistic Concurrency Control is based on the assumption that database transactions mostly don't conflict with other transactions, and that allows OCC to be as permissive as possible in allowing transactions to execute.
		Unfortunately, if there are many conflicts, the cost of repeatedly restarting transactions, hurts performance significantly -- other non-lock concurrency control methods have better performance when there are many conflicts.
	en.wikipedia.org /wiki/Optimistic_concurrency_control (302 words)

	Concurrency control (Site not responding. Last check: 2007-11-03)
		In computer science -- more specifically, in the field of database s -- concurrency control is a method used to ensure that database transaction s are executed in a safe manner (i.e., without data loss).
		Concurrency control is especially applicable to relational database s and database management system s, which must ensure that transactions are executed safely and that they follow the ACID rules.
		Control Application and Maintenance, Inc. Providing customized industrial process control instrumentation and control systems to the process control industries of the US.
	www.serebella.com /encyclopedia/article-Concurrency_control.html (578 words)

	Concurrency control (Site not responding. Last check: 2007-11-03)
		In computer science -- more specifically in the field databases -- concurrency control is a method used to ensure database transactions are executed in a safe manner without data loss).
		Concurrency control is especially to relational databases and database management systems which must ensure that transactions are safely and that they follow the ACID rules.
		In 1986, "Control" was released and it offered more of a mature look to Janet, (who was 19 years old when the album was released) from her two prev...
	www.freeglossary.com /Concurrency_control (556 words)

	Using concurrency control: WebSphere Application Server (Site not responding. Last check: 2007-11-03)
		Concurrency control addresses the competing requirements of applications that require read access to data against those of applications that require update access.
		Additionally, for optimistic concurrency control, the access intent of the first method in the transaction does not determine whether FOR UPDATE is used in the SQL SELECT statement.
		The default concurrency control scheme of pessimistic with default isolation levels is a reasonable choice for this bean cache configuration.
	www-3.ibm.com /software/webservers/appserv/doc/v40/ae/infocenter/was/rn111083.1.html (1793 words)

	Mimer Developers - Features - Transaction Concurrency - Optimistic Concurrency Control
		In a pessimistic concurrency control system, it is possible to get into a situation where a number of transactions are waiting on each other, a situation known as a deadlock, where none of the transactions can proceed.
		Through the use of optimistic concurrency control, Mimer SQL is able to avoid problems such as data being left inaccessible because of locks being held over user interactions or client processes failing.
		A solution to lock thrashing offered by the vendors to their customers, is to reduce the number of concurrent transactions in the system by restricting the number of server sessions, that is, throttle the throughput of the database server.
	developer.mimer.com /features/feature_15.htm (1596 words)

	Citations: Apologizing versus asking permission: Optimistic concurrency control for abstract data types - Herlihy ...
		Concurrency control schemes proposed in [Kor83, SS84, Wei88, Wei89] define the notion of conflict between arbitrary operations in terms of commutativity (operations conflict if and only if they do not commute)....
		TSTE is not a new concurrency control algorithm.
		There is a superficial similarity between optimistic concurrency control algorithms [6] and TSTE, especially its optimistic variant, because they both adopt....
	citeseer.ist.psu.edu /context/86308/0 (2153 words)

	Non-lock concurrency control - Wikipedia, the free encyclopedia
		In computer science, in the field of databases, non-lock concurrency control is concurrency control method used in relational databases without using locking.
		They involve the use of timestamps on transaction to determine transaction priority.
		Optimistic concurrency control (should Optimistic concurrency control and Non-lock concurrency control be merged ?)
	en.wikipedia.org /wiki/Non-lock_concurrency_control (91 words)

	Concurrency Control in Real Time Databases (Site not responding. Last check: 2007-11-03)
		The Speculative Concurrency Control approach relies on the use of redundant computations to start on alternative schedules, as soon as conflicts that threaten the consistency of the database are detected.
		OCC and PCC techniques are characterized by blockages and rollbacks which have a negative impact on the performance of the RTDBSs.
		A related topic is the index based concurrency control research on which is being conducted by the RICC group at the Indian Institute of Science and Indian Institute of Technology, Bombay, India.
	www.cs.uah.edu /~thinke/CS687/Fall97/Tech/abraham.html (2092 words)

	PatHelland's WebLog : More Discussion of SOA is like the Night Sky...
		That's optimistic concurrency, each of us had the 'booking number' and 'what we thought we knew about the state of the booking', my wife probably wouldn't have asked to change the room for a booking she knew was cancelled.
		Obviously my big thing is optimistic concurrency, if something needs to be shouted to the development community in general it isn't that 'loose-coupling is important' it's 'optimistic concurrency is crucial!'.
		The thing about an 'optimistic lock' is that it is 'implicit' and you have it as soon as you have a copy of some data.
	blogs.msdn.com /pathelland/archive/2004/03/22/94000.aspx (15631 words)

	Optimistic Concurrency Control (Site not responding. Last check: 2007-11-03)
		They can reduce concurrency unnecessarily (because locks are kept longer than necessary to avoid cascaded aborts) or lead to cascaded aborts (consider Figure 1).
		Optimistic concurrency control divides a transaction into a read phase, a validation phase, and a writing phase.
		Optimistic transactions also have the disadvantage that they do not allow increment sharing of transaction actions, thereby limiting concurrency.
	www.cs.unc.edu /~dewan/242/s04/notes/trans/node8.html (350 words)

	O/R Mappers: Optimistic Concurrency
		Optimistic concurrency works by adding some portion of the record's original values to the where clause of the update statement to make sure no one else has updated it first.
		Next, it allows the flexibility to define your concurrency fields, which is missing from at least some other systems -- great if you are using TimeStamp or if have you have so many fields that you don't want to pass them all -- which was something else I had just dealt with.
		I totally agree that optimistic concurrency is often, and incorrectly, given a very lofty place.
	weblogs.asp.net /pwilson/archive/2004/03/05/84852.aspx (1322 words)

	Concurrency Control and Data Integrity
		In case of optimistic concurrency, clients are written to handle possible rollbacks of some of the parallel transactions.
		The main advantage of optimistic concurrency control method is faster response time, but on the downside you cannot be sure that the action will be performed until the lock has been accepted or rejected.
		For example, if there are many users, the probability of concurrent access is greater and so pessimistic concurrency control might be used, whereas if many users don't exist, concurrent access will be rarer so optimistic concurrency control might be better used.
	www.pramati.com /docstore/1230022/tref_concurrency.htm (1774 words)

	O/R mappers and concurrency control
		This means that, besides the point that there is no silver bullet to solve all concurrency problems, it is also not possible to define a common way to supply concurrency control: different developers will implement concurrency control differently, or at least: want to use it differently.
		Concurrency control as flexible as you can possibly get, and usable not only on a per-type basis but also on a per-instance basis.
		If you want higher level concurrency functionality, it is not wise to implement that on a low level, so it's in all cases more wise to simply add logic which prevents low level concurrency violations pop up like multi-edits of the same row.
	weblogs.asp.net /fbouma/archive/2004/03/06/85125.aspx (1741 words)

	Concurrency Control
		The Bean pool size is a measure of concurrency and not the database size and since bean activation/passivation are not expensive operations when commit, option is set to Non-Exclusive.
		Use Case Scenario If the bean is highly concurrent in its usage, the container managed fields rarely get modified as part of transaction, and the modified bean state is dependent on the initial state of the bean at the beginning of transaction.
		Use case Scenario If the concurrency is high on the bean and the modification of bean's CMF is not dependent on the previous state of the bean, isolation could potentially overwrite changes from multiple concurrent transactions.
	www.pramati.com /docstore/1230006/help/deploytool/concurrency.htm (1920 words)

	Abstracts of Some Papers and Patents Authored by IBM Fellow Dr. C. Mohan of IBM Almaden Research Center
		These techniques are also applicable to the concurrency control of the classical links-based storage and access structures which are beginning to appear in modern systems also.
		Concurrent key record inserts or deletes are permitted throughout the index tree where no indication of a pending structure modification operation is present and are delayed where a pending structure modification operation is indicated.
		A method of controlling entry of a block of data is used with a high-speed cache which is shared by a plurality of independently-operating computer systems in a multi-system data sharing complex.
	www.almaden.ibm.com /u/mohan/aries_papers.html (14753 words)

	Transaction Control
		Transaction control provides a means of protecting the database from corruption which might arise from two users attempting to the change the same information at the same time and also provides the basis for ensuring database consistency, see Database Consistency.
		Mimer SQL transaction management uses Optimistic Concurrency Control, which is described in the Mimer SQL Programmer's Manual.
		Transaction control behavior in application programs and a number of the system facilities, notably Backup and Restore - see Backup and Restore, is controlled at the databank level by setting the option (LOG, TRANS or NULL) for the databank.
	developer.mimer.com /documentation/Mimer_SQL_System_Management/DB_environment12.html (441 words)

	[No title] (Site not responding. Last check: 2007-11-03)
		Optimistic concurrency control differs from the use of locks fundamentally, in that it is based on the assumption (observation) that in many systems, the vast majority of operations are independent.
		This is so that when there is a fault that leads to some partial failure in the system, the task of rolling back the whole system to a know state is a tractable one, since the system is modularised.
		The idea of optimistic concurrency control is that by analysing the dependencies, one can generate ``commit guards''.
	www.cs.ucl.ac.uk /staff/J.Crowcroft/ods/node93.html (256 words)

	Optimistic Concurrency Control
		I ran some quick and dirty comparisons of the performance for the three methods of optimistic concurrency control that I discuss in my book together with the ordinary method used by Datasets of ADO.NET.
		To test on your own, you can use the code I wrote for my presentation called “Managed concurrency control of disconnected data” at VS Live in May 2002.
		As you can see, the overhead isn’t that large in full roundtrip scenarios, but when you compare it only between stored procedures, the difference is something like 1 to 7 compared to before and after values (optimistic concurrency control).
	www.jnsk.se /book/download/optimistic.htm (200 words)

	Arbeitsbericht Nr. 30 (Site not responding. Last check: 2007-11-03)
		Several years ago optimistic concurrency control gained much attention in the database community.
		Concerning traditional database systems most developers felt that pessimistic concurrency control might not be the best solution for concurrency control, but, a well-known and accepted one.
		With the work on new generation database systems, however, there has been a revival of optimistic concurrency control (at least a partial one).
	dawis2.informatik.uni-essen.de /site/publications/papers/arbber/ab30.html (133 words)

	Optimistic and Pessimistic Concurrency (Accessing and Changing Relational Data (SQL Server)) (Site not responding. Last check: 2007-11-03)
		Microsoft® SQL Server™ 2000 offers both optimistic and pessimistic concurrency control.
		Optimistic concurrency control works on the assumption that resource conflicts between multiple users are unlikely (but not impossible), and allows transactions to execute without locking any resources.
		Pessimistic concurrency control locks resources as they are required, for the duration of a transaction.
	msdn.microsoft.com /library/en-us/acdata/ac_8_con_7a_57p5.asp?... (114 words)

	Optimistic Concurrency Control (Site not responding. Last check: 2007-11-03)
		concurrency control procedures maintain sets of objects accessed by transaction.
		serial equivalence: if have individual transactions that are executed concurrently, have serial equivalence if there exists some serial sequence of the transactions that produce the final data structure.
		analysis for large B-trees shows that optimistic concurrency control is a win - very rare that one insertion would cause another concurrent insertion to restart.
	swig.stanford.edu /pub/summaries/database/optimistic_concurrency.html (464 words)

	MS-Thesis
		Concurrency control algorithms attempt to provide correctness of concurrent execution of transactions.
		Various algorithms for concurrency control in database systems are presented in the literature.
		Comparing algorithms it is shown that in low contention environment, optimistic concurrency control has the best throughput, while in high contention, best throughput obtained from restart oriented locking methods.
	mehr.sharif.edu /~hfaili/msindex.htm (216 words)

	Citations: Distributed Optimistic Concurrency Control Methods for High-Performance Transaction Processing - Thomasian ... (Site not responding. Last check: 2007-11-03)
		In case of concurrent writes on an object operations may be rolled back.
		Optimistic concurrency control occurs in four steps: 1.
		Distributed optimistic concurrency control methods for high- performance transaction processing.
	citeseer.ist.psu.edu /context/727531/0 (737 words)

	Page-based optimistic concurrency control for memory-mapped persistent object systems (Site not responding. Last check: 2007-11-03)
		In this page-grain environment, conventional concurrency control schemes do not work as well as they do in the object-grain environment for business applications, because of their lack of efficiency and/or correctness.
		Existing optimistic schemes sometimes provide inconsistent views of the persistent storage to transactions that are to be aborted.
		The optimistic scheme with versioning avoids lock contention, commits all read-only transactions, and provides consistent views of the persistent storage even to transactions that are to be aborted.
	csdl.computer.org /comp/proceedings/hicss/1995/6935/00/69350645abs.htm (314 words)

	Bounded Locking for Optimistic Concurrency Control (ResearchIndex) (Site not responding. Last check: 2007-11-03)
		Abstract: Optimistic methods of concurrency control are gaining popularity.
		This is especially true with the resurgence of mobile and distributed databases, which inherently rely on optimistic techniques to improve availability and performance of the database system.
		A key problem with optimistic techniques is that they do not perform well in highly conflict prone environments.
	citeseer.ist.psu.edu /150623.html (339 words)

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