HP 3000 Manuals

Silhouette Reference Manual

Silhouette Functions 

Silhouette provides the benefits of high system availability, database
availability during system backup, and load balancing across multiple
systems.

High System Availability 

Silhouette maintains up-to-date duplicate TurboIMAGE databases on both
the primary system and the secondary system(s).  If a system failure
occurs on the primary system, Silhouette control is switched to the
secondary system and operation continues.  A two-part report is then
generated for each user.  It shows the last complete transaction
processed and a list of incomplete transactions, which indicates to the
user where to resume processing.  Since all incomplete transactions are
automatically removed from the secondary database, data integrity is
ensured.

Transactions can update either single or multiple databases.  If a
failure occurs in the middle of a super transaction (a transaction that
updates multiple data items or multiple databases), Silhouette removes
the records of the incomplete super transaction from the TurboIMAGE
databases.

Figure 1-2 shows how Silhouette provides high system availability by
switching control from the primary system to the secondary system in case
the primary system fails.


          Figure 1-2.  Switching Systems for High Availability 

Database Availability During System Backup 

Silhouette duplicates databases from a primary system to a secondary
system.  This allows you to perform a system backup, at your convenience,
using the secondary system.  Operation on the primary system is not
interrupted, allowing access to critical database applications 24 hours a
day.

During the backup new transactions on the primary system are stored in a
logfile, and if necessary, stored to tape.  After backup of the databases
on the secondary system is completed, Silhouette transmits any new
records from the primary system to the secondary system, resynchronizes
the duplicate database, and brings it up-to-date.

Figure 1-3 shows performing a system backup on the secondary system while
the data on the primary system continues to be processed and logged.


          Figure 1-3.  Silhouette Backup on Secondary System 

Load Balancing 

Silhouette allows inquiry-only access to duplicated TurboIMAGE databases
on the secondary system(s).  With this capability read-only users are
moved from the primary system to the secondary system, reducing the
workload on the primary system.

This application is particularly suited when using multiple secondary
systems which allows more users simultaneous access to the database.  By
appropriately configuring the systems, users on both the primary system
and secondary system(s) benefit from improved system response time.

Figure 1-4 shows how additional users can access the databases and
improve response time.


          Figure 1-4.  Balancing System Load 

MPE/iX 5.0 Documentation