Depending on organization structures within a company, ever-increasing demands are being made on OLTP applications with regard to availability:
backup systems must be started automatically in the event of an error
the bulk of maintenance operations must be performed during normal operation.
In this regard, SESAM/SQL provides a number of functions which allow it to satisfy these requirements.
Dynamic reconfiguration of the DBH session
The DBH administration commands RECONFIGURE-DBH-SESSION and RELOAD-DBH-SESSION are also available to the SESAM/SQL system administrator for increasing the availability of the independent DBH, for importing a correction version of the DBH while DBH operation is in progress, and for dynamic reconfiguration of the DBH session (see the “Database Operation” manual).
Both administration statements are executed without interrupting the DBH session. From the user viewpoint no DBH failure occurs.
Automatic extension of database limits
If, as a result of extensive additions and updates, the defined limits of the database prove to be too narrow, they are extended automatically during the session. Because the extension is performed automatically, availability is increased considerably.
Online data definition and utilities
Database administration tasks such as loading, backing up and applying the modifications logged in the logging files to SESAM backups can be performed during normal operation, i.e. the database does not have to be deactivated.
Databases can also be built online. The logical database description (schema) of an existing database can also be modified online.
This means that situations in which a database has to be deactivated only occur extremely rarely.
Using replications
A replication is a copy of a database which can be used to restore a database, or it can be used as a shadow database for a recovery.
Using replications as shadow databases can speed up recovery considerably.
Utilization of foreign copies
With SESAM/SQL-Server it is possible to create foreign copies without having to shut down database operation. In addition, foreign copies can be used directly for recovery purposes, i.e. without having to use a replication.
Utilization of the warm start time
SESAM/SQL-Server makes it possible to start OLTP operation even during the warm start period and also allows you to influence its duration.
Space concept
SESAM/SQL derives the physical structure of the database automatically from the logical database description (schema).
The Storage Structure Language (SSL) allows users to optimize the organization of storage space in accordance with their own particular needs, thus enabling them to accelerate certain accesses, for instance. One of the measures which affects the storage structure is the physical division of the database into a maximum of 1000 spaces (files). This means that it is often only possible to deactivate the relevant spaces rather than the entire database. This means, for instance, that backup operations or recovery of corrupt portions of the database can be restricted to individual spaces.
On pubsets with “large files” a space can be up to 4 TB in size. Otherwise it can be up to 64 GB in size.