SQL/MX 2.x Installation and Management Guide (H06.10+, J06.03+)

Managing Database Applications
HP NonStop SQL/MX Installation and Management Guide—544536-007
11-13
Managing Permissions for Files in Guardian Space
the group ownership of a file, use the chgrp command. To change group ownership,
you must be a member of the group from which you are changing the file.
For more information about these and other OSS commands, see the Open System
Services User’s Guide.
Managing Permissions for Files in Guardian Space
For SQL applications programs stored in Guardian space, you control access to the
files with these user interfaces:
•
TACL commands and programs to manage user and logon security
•
File Utility Program (FUP) commands to manage disk file security
•
Safeguard software to provide additional security features for systems and
distributed database environments
For more information, see the Guardian User’s Guide and the Safeguard User’s Guide.
Maintaining Query Execution Plan Validity
A query execution plan defines the semantics and execution characteristics for a single
compiled SQL statement. Statically compiled applications typically have many query
execution plans. The query execution plans of an application are stored in an SQL/MX
user module. Globally placed modules are stored in the
/usr/tandem/sqlmx/USERMODULES directory. Locally placed modules are stored in
the same directory as the C, C++, or COBOL executables that use them.
It is important to maintain valid query execution plans for the optimal performance of
the database applications in a production environment. This subsection describes the
factors that affect the validity of query execution plans and provides guidelines for
recompiling, displaying, and analyzing query execution plans.
Factors Affecting the Query Execution Plan
Changes to the table structure or the distribution of data in a table can cause a
compiled query execution plan to become invalid. When the SQL/MX executor detects
these changes at run time, it forces automatic recompilation of the query execution
plan. Automatic recompilation incurs a performance cost because it requires the query
execution plan to be regenerated at run time and stored in memory. The automatically
recompiled plan is not saved for subsequent executions of the same program or for
multiple concurrent executions of the same program. Therefore, the plan must be
regenerated each time the application runs. Because of this behavior, automatic
recompilation might be unsuitable for some production environments.
To ensure the optimal performance of database applications in a production
environment, either prevent the occurrence of automatic recompilation or detect its
occurrence: