Introduction to Data Management

Accessing Databases With NonStop SQL
3-4 15873 Tandem Computers Incorporated
Processing Speed
and Power
Unlike most relational database management systems, NonStop SQL is fast and
powerful enough to handle large quantities of rapidly changing data. NonStop SQL
was specifically designed to manage heavy OLTP demands without sacrificing
performance. Many users can update data simultaneously, recording data in the
database as it is entered. NonStop SQL can process many simultaneous online
transactions while still providing the rapid response time needed by a dynamic OLTP
environment.
Support for
Distributed Systems
Because NonStop SQL is integrated with other Tandem software, it can be used for
applications that run in vast global networks of systems. With a fully distributed
database, applications that run at one system can easily access and modify data
located at other systems. In fact, NonStop SQL allows you to divide individual tables
across the systems in your network. With this approach, data is stored where it is
used most often—but it remains available to all users everywhere in the network.
Applications themselves can also be distributed, with screen-managing requesters on
one system sending data to database-handling servers on another system.
Data Integrity NonStop SQL provides data integrity, ensuring that the data in your database always
has the correct values. NonStop SQL supports this integrity by:
Ensuring that any data value entered in the database is the correct type (character
or numeric) and size for the column that will hold that value
Optionally checking values entered against constraints that you can specify on
columns, perhaps to ensure that each value falls within a specified range or that it
relates properly to other values in the table
Optionally verifying that all values entered in certain columns are unique, so that
individual records can be identified without ambiguity
This automatic checking saves you the trouble of providing checking routines in your
program code. When NonStop SQL detects a violation, it rejects the data with an
explanatory message.
Data Consistency NonStop SQL provides data consistency by ensuring that changes to your database
are either made completely, or that they are not made at all. With many transactions
executing at the same time, each transaction must finish without interference from
other concurrent transactions. NonStop SQL uses the Transaction Monitoring Facility
(TMF) to ensure that user transactions leave your database in a consistent state that
mirrors the real world that the database models. If a transaction does not complete
successfully, TMF returns the affected part of the database to its condition prior to the
start of the transaction. If a hardware or software component fails, TMF recovers the
data impacted by the failure.
Although the data dictionary is always protected by TMF, transaction protection for
tables in your database is optional. For each particular table, NonStop SQL allows
you to request or withhold this TMF protection.
More information about TMF appears in Section 7.