Distributed processing based on SESAM/SQL-DCN can be used in the following applications:
When distributed databases are used, it is possible to work with databases on different computers within one session. The data can be stored on the computer on which it is required most frequently. The SESAM/SQL database is the distribution granularity.
Configurations can communicate with one another (on one computer, or on other computers across a network).
The following features characterize distributed processing based on SESAM/SQL-DCN:
The application programs' independence of database locations:
The location of a database is irrelevant for the application programs. It is determined internally by the system and is not addressed explicitly by the application programs. The programs are therefore not affected by changes to the location. In particular, application programs used to date in a non-distributed context can be used in a distributed context without modification. The distribution of the databases is something that is transparent to the application programs.Two-phase commit at the end of a transaction:
Multi-computer transaction logging guarantees the security of transaction-oriented network-wide processing of data. This allows updates to multiple databases within one transaction, as well as automatic recovery after a system failure (see section “Restart”).Deadlock and longlock detection:
Deadlocks and longlocks are recognized and resolved by the system beyond the boundaries of a single computer.
Distributed databases offer the following advantages:
Higher performance:
Throughput may be improved by processing user requests on different computers.Higher level of availability:
Several data-processing systems that can, if necessary, be operated stand-alone, ensure that the failure of one computer does not affect all of the data-processing procedures.Adaptable organization:
Working procedures need not be centered on a single computer center.Flexibility in terms of expandable capacity.
Operating modes of a SESAM/SQL-DCN application
Distributed processing with SESAM/SQL-DCN can be carried out in timesharing mode (TIAM) and in transaction mode. Timesharing mode can be implemented through the use of the Universal Transaction Monitor openUTM or the data communication system DCAM.