HP 3000 Manuals

ALLBASE/SQL Performance and Monitoring Guidelines

Overhead Generated by SQLMON 

In most cases, SQLMON has little impact on system performance.  However,
be careful when you use the SampleIO subsystem, because it can generate
enough overhead to impact the performance of other DBEnvironment
sessions.

Be careful also when you use the Static subsystem.  The Static subsystem
differs from the other SQLMON subsystems, because it establishes a
connection with the DBEnvironment.  When you leave the Static subsystem
for another subsystem, the connection closes.

SQLMON obtains information on the primary screen in the subsystem, the
Static screen, when you issue a SET DBENVIRONMENT command.  System
performance should not be affected when you access the Static screen.

However, when you access other screens in the Static subsystem, SQLMON
issues commands that are similar to the UPDATE STATISTICS statement.
These commands perform serial scans on each DBEFileSet, which can be very
time consuming (however, the commands do not update statistics in the
system catalog or invalidate stored sections).  SQLMON does not acquire
locks on user tables during this processing.

To improve performance, you can issue the command

     SET DBEFILESET DBEFileSetName 

which improves performance, because

   *   SQLMON obtains information only about the objects in
       DBEFileSetName, thereby reducing the number of serial scans that
       must be performed

   *   Serial scans are performed only once on DBEFileSetName.  Serial
       scans occur the first time you access a screen other than the
       primary screen in the subsystem, not when you issue the SET
       DBEFILESET command.  When you access another screen in the
       subsystem, you view information obtained during the original
       scans.

If the DBEFILESET variable is OFF, SQLMON performs scans on each
DBEFileSet each time that you access a screen in the Static subsystem.

MPE/iX 5.0 Documentation