SQL/MP Programming Manual for C

Program Invalidation and Automatic SQL
Recompilation
HP NonStop SQL/MP Programming Manual for C—429847-008
8-6
Causes of Automatic Recompilation
Automatic SQL recompilation performs these functions:

Uses the current description of the database to determine the most efficient access
path for each referenced database object

Maximizes database availability and node autonomy by generating a new
execution plan at run time

Allows a program to reference database objects that did not exist during explicit
SQL compilation

Allows a program to use a new set of DEFINEs to specify a different database (for
example, a development database rather than a production database)
You can enable or disable automatic SQL recompilation when you explicitly SQL
compile a program. The RECOMPILE option (the default) enables automatic SQL
recompilation, whereas the NORECOMPILE option disables it.
Causes of Automatic Recompilation
If automatic SQL recompilation is enabled (the NORECOMPILE option is not
specified), the SQL executor invokes the SQL compiler to recompile a program or
statement (depending on the RECOMPILEALL or RECOMPILEONDEMAND option) in
these situations:

The program file is marked invalid at SQL load time.

The DEFINE values at SQL load time are different from the DEFINE values used
to explicitly SQL compile the program.

The timestamp check fails for an SQL object referenced in an SQL statement.

An unavailable access path (index) exists.

The program file contains an uncompiled SQL statement.
In some cases, you can prevent automatic recompilation using the similarity check. For
more information, see Preventing Automatic Recompilations
on page 8-9.
Invalid SQL Program File
SQL load time occurs when the SQL executor runs the first SQL statement in a
program. If the SQL program on disk is invalid for any of the reasons listed in Causes
of Program Invalidation on page 8-2, the SQL executor forces the recompilation of the
program or statement. To control the automatic recompilation, specify the
RECOMPILEALL option (the default) to cause the recompilation of the entire program
or the RECOMPILEONDEMAND option to limit the recompilation to statements
actually run.