DB Projects Help >> Recovery techniques
Restoration methods or techniques are methods to guarantee .Transaction atomicity and strength despite failures
The recovery subsystem, using recovery criteria, ensures atomicity by undoing the measures of dealings
That do not make and strength by generating sure that all Actions of dedicated dealings endure even if breakdowns occur.
Two major strategies in recovery process
Log-based recovery using WAL method.
Shadow-paging
Restoration Techniques:
Salvation program: Run after a collision to try to recover the system to a real state. No recovery information used. Used when all other methods crash or were not used. Good for conditions where buffers were missing in a collision and one wants to recover what was lost
Incremental dumping: Altered information files ripped to store after job carried out or at intervals
Audit trail: Series of measures on information files are noted. Optimum for "backing out" of dealings. (Ideal if path is published out before changes)
Differential files: Individual information file is managed to keep on top of changes, regularly joined with the main file
Backup/current version: Provide information files kind the existing edition of the collection. Files containing earlier principles kind a regular copy edition.
Multiple copies: Many effective reports of each information file are managed during standard function of the collection. In conditions of disaster, assessment between the editions can be used to find a regular edition.
Careful replacement: Nothing is modified in place, with the unique only being removed after function is total.
(Parens and statistics are used to indicate which amounts from above are recognized by each technique).
Combinations of two methods can be used to provide identical safeguard against different types of breakdowns. The methods above, when executed, power changes to:
The way information is set up the way information is modified and controlled nothing (available as utilities)
Recovery concepts
The procedure of remedy any type of collection breakdowns, quickly and without information reduction and keep collection substantial available is called collection restoration. The main elements of collection restoration are the most recent collection copy. If you keep collection copy effectively, then collection restoration is very simple procedure.
The elements and technological innovation of collection is to manage to reduce or no information reduction and keep collection for start, includes
* Checkpoints
* Management file
* Online redo log files
* Aged update log file
* Expensive Recovery Area
Recovery Technologies
* Database Expensive back technology
* Open collection in Store log mode
* Apply collection substantial availableness features like RAC, DATAGUARD, steams etc.
Components of collection recovery
Checkpoints: - Gate (CKPT) in oracle collection is an essential background procedure. This procedure works in show with the collection writer procedure (DBWn) to manage how long required for example restoration. Gate in oracle takes place when guide or automated log switch takes place. FIRST_START_MTTR_TARGET parameter can be changed to handle check points as a result to improve example restoration.
Control information file - Management information file is a meta-data library for collection. It keeps all information about structure of the collection. Management information file is a very critical for collection function, so as being a DBA,you should maintain at minimum two reports of handle information file ( Oracle recommend three ) and save these in a different drive to save the handle information file drive breakdowns.
Concurrency control techniques
In it and computer research, especially in the areas of on-line (see also contingency encoding, similar programming), techniques (see also similar computing), multiprocessors, and directories, concurrency management guarantees that correct effects for contingency businesses are created, while getting those effects as quickly as possible.
Computer techniques, both software and components, include quests, or elements. Each element is designed to work effectively, i.e., to respect to or meet certain reliability regulations. When elements that work as well work together by text messages or by giving used data (in memory or storage), a certain component's reliability may be broken by another element. The general area of concurrency management provides regulations, methods, design methods, and concepts to maintain the reliability of elements running as well while communicating, and thus the reliability and correctness of the whole program. Presenting concurrency management into a program means applying function demands which typically result in some overall performance reduction. Operation reliability and correctness should be obtained with as good as possible overall overall performance,
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