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Facilité d'utilisation
Introduction to NonStop SQL/MP
A Highly Available Database
A Highly Available
A NonStop SQL/MP database is highly available, remaining online for current users
Database
even when, for example, you scale up the database to accommodate growing business.
NonStop SQL/MP provides availability, just as it provides high performance and
scalability, by combining features inherent in the Tandem system architecture and
NonStop Kernel with features specific to NonStop SQL/MP.
Availability Features of the
The NonStop Kernel operating system uses process pairs to provide fault tolerance. A
NonStop Kernel
system process, or an application process that requests database services from an
application server process, can have a backup process executing in another CPU. If a
fault occurs in the primary CPU, the backup process can take over without
interrupting the application. Moreover, process pairs do not require special
programming. For transactions that access the database, NonStop TM/MP helps to
ensure availability by recovering the transactions in case of a system failure.
You can enhance the availability of the database by storing the data for each disk
volume on two identical disks. This feature, called disk mirroring, protects data from
hardware faults that could affect any individual disk. If one disk becomes
inaccessible, the mirrored disk continues to be available, and there is no impact on the
application.
Tandem also provides software to protect against a disaster affecting an entire site.
NonStop SQL/MP works with the Remote Duplicate Database Facility (RDF) product,
which lets you maintain a duplicate database on a separate system at a remote
location. As users modify the primary database, RDF replicates the changes on the
duplicate (backup) database. You can configure RDF so that multiple remote systems
maintain backup databases for one another, providing data replication. Each system
can then support primary application activity (such as OLTP or query processing) as
well as providing for disaster recovery for another system.
Availability Features of
NonStop SQL/MP provides several features that make it possible to keep the database
NonStop SQL/MP
continuously available to your application. Process pairs (mentioned earlier) are
especially valuable when applied to the data access manager. You can configure the
data access manager to have a backup process in another processor. If a failure should
occur in the CPU in which the primary data access manager resides, the alternate data
access manager can immediately take over the job of retrieving data so that the in-
process query can complete successfully.
In addition, NonStop SQL/MP ensures that application programs never have to fail
when they access database objects that have been changed by the DBA. The active
data dictionary, which records all changes made to database objects and reflects the
current status of the database, flags each application program that accesses a modified
object. (Database objects include tables, indexes, views, programs, and collations.)
NonStop SQL/MP automatically recompiles an SQL query if the existing execution
plan (the compiled, executable code) has been invalidated because of a modified
database object.
If a modification does not significantly alter a database object, the existing execution
plan may execute acceptably, if perhaps inefficiently. NonStop SQL/MP provides an
option to allow the existing plan to execute even after a table or other object the plan
113425 Tandem Computers Incorporated
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... Ce manuel est également adapté pour les modèles :
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