Database general Knowledge

backup and recovery

This is a test post

posted by Unknown @ 7:28 AM 0 Comments

Dead Lock

A deadlock is a situation wherein two or more competing actions are waiting for the other to finish, and thus neither ever does. It is often seen in a paradox like 'the chicken or the egg'.

In the computing world deadlock refers to a specific condition when two or more processes are each waiting for another to release a resource, or more than two processes are waiting for resources in a circular chain (see Necessary conditions). Deadlock is a common problem in multiprocessing where many processes share a specific type of mutually exclusive resource known as a software, or soft, lock. Computers intended for the time-sharing and/or real-time markets are often equipped with a hardware lock (or hard lock) which guarantees exclusive access to processes, forcing serialization. Deadlocks are particularly troubling because there is no general solution to avoid (soft) deadlocks.

One known algorithm that is used for deadlock avoidance is the Banker's algorithm, which requires resource usage limit to be known in advance. However, for many systems it is impossible to know in advance what every process will request. This means that deadlock avoidance is often impossible.


The Banker's algorithm is a resource allocation & deadlock avoidance algorithm developed by Edsger Dijkstra that tests for safety by simulating the allocation of pre-determined maximum possible amounts of all resources, and then makes a "safe-state" check to test for possible deadlock conditions for all other pending activities, before deciding whether allocation should be allowed to continue.

The algorithm was developed in the design process for the THE operating system and originally described (in Dutch) in EWD108[1]. The name is by analogy with the way that bankers account for liquidity constraints.

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posted by Unknown @ 12:39 PM 0 Comments

ER-Diagram

Databases are used to store structured data. The structure of this data, together with other constraints, can be designed using a variety of techniques, one of which is called entity-relationship modeling or ERM. The end-product of the ERM process is an entity-relationship diagram or ERD. Data modeling requires a graphical notation for representing such data models. An ERD is a type of conceptual data model or semantic data model.

The first stage of information system design uses these models to describe information needs or the type of information that is to be stored in a database during the requirements analysis. The data modeling technique can be used to describe any ontology (i.e. an overview and classifications of used terms and their relationships) for a certain universe of discourse (i.e. area of interest). In the case of the design of an information system that is based on a database, the conceptual data model is, at a later stage (usually called logical design), mapped to a logical data model, such as the relational model; this in turn is mapped to a physical model during physical design. Note that sometimes, both of these phases are referred to as "physical design".

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posted by Unknown @ 1:12 PM 0 Comments

Telecom Database General Knowledge

Database in Telephone Exchange is nothing but the set of Rules/Protocols book for the Telephone exchange processor to follow for each subscriber input to the exchange.
The input to a basic telephone exchange is digits dialed by the subscriber for the need of connection to the dialed number to make a voice call.

In the telephone exchange all the records will be created in a normal database TABLE format. Let us take a example of a Landline Telephone exchange and the database model in that.

Table name and the relation.

1. SUBSCRIBER TABLE : Relation between the Hardware Port number where the telephone is connected and the Telephone number itself.
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2. TRUNK TABLE : Relation between the connection between the hardware ports between the exchanges.
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3. TRUNK GROUP TABLE : Relation between the Signalling connection between exchanges and the TRUNKs.
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4. ROUTE TABLE : Relation between the DESTINATION and the TRUNK GROUP.
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5. DESTINATION TABLE : Relation between the ROUTE and the CODE.
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6. CODE TABLE : Relation between the DESTINATION and the Dialed digits (CODE).
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7. CHARGE TABLE : Relation between the CHARGING DETAILS and the Dialed digits (CODE).

posted by Unknown @ 6:03 AM 0 Comments