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288:: Requires enough RAM to hold the entire system state. State changes made to a system after its last image was saved are lost in the case of a system failure or shutdown. Saving an image for every single change would be too time-consuming for most systems, so images are not used as the single persistence technique for critical systems.
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is an example of orthogonal persistence using a system image because it does not require any actions by the programs running on the machine. An example of non-orthogonal persistence using a system image is a simple text editing program executing specific instructions to save an entire document to a
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This technique is the writing to storage of only those portions of system state that have been modified (are dirty) since their last write. Sophisticated document editing applications, for example, will use dirty writes to save only those portions of a document that were actually changed since the
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The term "persistent" was first introduced by
Atkinson and Morrison in the sense of orthogonal persistence: they used an adjective rather than a verb to emphasize persistence as a property of the data, as distinct from an imperative action performed by a program. The use of the transitive verb
197:" or "transparent" when it is implemented as an intrinsic property of the execution environment of a program. An orthogonal persistence environment does not require any specific actions by programs running in it to retrieve or save their
330:: When journals are used exclusively, the entire (potentially large) history of all system events must be reapplied on every system startup. As a result, journals are often combined with other persistence techniques.
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The entire "Undo/Redo" history of user commands in a picture editing program, for example, when written to a file, constitutes a journal capable of recovering the state of an edited picture at any point in time.
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use a combination of the dirty writes and transaction journaling techniques mentioned above. They provide not only persistence but also other services such as queries, auditing and access control.
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This technique requires state changes to be intercepted within a program. This is achieved in a non-transparent way by requiring specific storage-API calls or in a transparent way with automatic
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that makes it easier for a program to persist its state is generically called a persistence layer. Most persistence layers will not achieve persistence directly but will use an underlying
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Using journals is the second simplest persistence technique. Journaling is the process of storing events in a log before each one is applied to a system. Such logs are called journals.
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Non-orthogonal persistence requires data to be written and read to and from storage using specific instructions in a program, resulting in the use of
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On startup, the journal is read and each event is reapplied to the system, avoiding data loss in the case of system failure or shutdown.
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that remain persistent even after a crash or unexpected shutdown. Operating systems that employ this ability include
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588:. 10th Australian National Computer Conference. Melbourne, Australia. pp. 70–79.
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where they are also called "transaction logs" or "redo logs".
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31:. For concepts relating to the persistence of memory, see
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Proceedings 10th
Australian National Computer Conference
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579:"PS-algol: A Language for Persistent Programming"
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608:University of Glasgow - School of CS - Research
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277:is the simplest persistence strategy. Notebook
210:On completion, the program persists the data
601:"Contracted Persistent Object Programming"
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131:Learn how and when to remove this message
599:Balzer, Stephanie (November 17, 2005).
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170:to the storage device data structures.
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246:Research prototype languages such as
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393:Database management systems (DBMSs)
80:"Persistence" computer science
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312:Journals are used by
161:computer data storage
652:Computer programming
617:on December 31, 2006
529:Java Persistence API
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65:improve this article
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450:single-level store
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339:last save.
279:hibernation
229:hibernation
149:persistence
636:Categories
555:References
241:VirtualBox
195:orthogonal
91:newspapers
448:with its
488:See also
292:Journals
252:Napier88
248:PS-algol
223:Adoption
455:Phantom
446:Multics
440:Coyotos
231:and in
206:persist
157:process
105:scholar
477:Lua OS
434:CapROS
423:KeyKOS
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273:Using
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465:IBM i
404:DBMSs
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112:JSTOR
98:books
623:2015
519:CRUD
428:EROS
399:DBMS
357:Any
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84:news
387:RAM
143:In
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