Overview General Base De Datos Adabas

Working of ADABAS


Description :


Adabas is one of the fastest databases in the world. Its high speed and legendary reliability make Adabas the ideal database server for large mission-critical business applications that require sub-second response times for thousands of users even during peak times. Adabas is available on mainframe, Windows, Unix and OpenVMS platforms.


Access toAdabas


Adabas can be accessed from Natural, Software AG’s 4GL development environment, from Bolero, Software AG’s application factory, and from every 3GL and 4GL that is equipped with a call interface.
In addition, Adabas can be accessed via standard interfaces such as ODBC or JDBC and, of course, embedded SQL can be used.






Data Storage


Data storage consists of the followingdisks:
Data
where user data is stored
Associator
where index information is kept
Work Area
where Adabas has its playground
Protection Log
where transaction data is kept temporarily for backup purposes
Command Log
where user commands are stored for backup purposes



Nucleus


This is the set of programs, tables, queues, etc. that make up Adabas.


Interface


This is theentrance to Adabas or, from an external point of view, the place where the calls are received and forwarded to the Adabas nucleus.


The Size of an Adabas Database


On the mainframe there is no size limit at all. On open-systems platforms the theoretical limit for Adabas databases is 128 TB - a figure limited in practice only by the amount of hard disk space that can be made available.Adabas – How it Works


➢ The Process Structure
➢ Data Storage
➢ Data and Index Compression
➢ Adabas Direct Access Method (ADAM)
➢ The Transaction Concept
➢ Universal Encoding Support
➢ Warm Restart




The Process Structure


Adabas is designed around a two-process structure; thus the Adabas nucleus executes in a separate partition of theoperating system from the application or the Adabas utility.
The Adabas nucleus manages all database activities and serves all user processes centrally. The number of users who can be served in parallel is unlimited and typically is many thousand users.
Normally one Adabas nucleus manages one Adabas database, although it is possible, for throughput reasons for multiple Adabas nuclei to manage oneAdabas database, this also includes the IBM Sysplex environment. On the mainframe there is no size limit at all. On Open Systems platforms the theoretical limit for Adabas databases is 128 TB - a figure limited in practice only by the amount of harddisk space that can be made available.
In order to be able to support thousands of users in parallel and deliver sub-second response times Adabassupports its own internal multi-threading architecture. This enables the Adabas nucleus to support an unlimited number of read and write tasks simultaneously. When a user request cannot be instantly fulfilled because it must wait for resources e.g. it must wait for an I/O operation to complete, then another user request will be serviced.
Further increases in performance is achieved in the I/Osubsystem with the following techniques:
data and index compression
asynchronous buffer flushing
buffer search algorithms based on hashing algorithms
The data compression reduces the data volume by nearly 50%. This means that with every I/O operation twice as much data is transferred and only half of the space is occupied in the I/O buffer.
Index compression can reduce the index data by as much as70% and results in similar saving.
The asynchronous buffer flush allows Adabas to continue updating data while the physical I/O process is in progress.
The hashing algorithm used by the I/O buffer results in equal search times irrespective of the buffer size. Thus as data volumes increase and the I/O buffer size is increased, there is no corresponding increase in the search time.


Data...