HP 3000 Manuals HP 3000 Manuals
The Stored Section
A section consists of ALLBASE/SQL instructions for executing an SQL
command. The SQL commands that do not generate stored sections are
listed in the "Stored Sections" paragraph of the "Using the ALLBASE/SQL
COBOL Preprocessor." Not every SQL command requires a section. For each
SQL command that does require a section, the preprocessor creates the
section and assigns to it a unique reference number. In the following
preprocessor generated code SQLSECNUM contains the number of the stored
section.
MOVE 1 TO SQLSECNUM
.
.
.
CALL SQLXCBL USING SQLXFET, SQLCA, SQLOWNER, SQLMODNAME,
SQLSECNUM, SQLTEMPV, SQLINLEN, SQLOUTLEN, SQLTRUE
Purpose of Sections
A section serves two purposes:
* Access validation: Before executing a stored section at run time,
ALLBASE/SQL ensures that any objects referenced exist and that
runtime authorization criteria are satisfied.
* Access optimization: If ALLBASE/SQL has more than one way to
access data, it determines the most efficient method and creates
the section based on that method. Indexes, for example, can
expedite the performance of some queries.
Runtime performance is improved by creating and storing sections at
preprocessing time rather than at run time.
Section Validity
A section is assigned one of two states at preprocessing time: valid or
invalid. A section is valid when access validation criteria are
satisfied. If the SQL command references objects that exist at
preprocessing time and the individual doing the preprocessing is
authorized to issue the command, the stored section is marked as valid.
A section is invalid when access validation criteria are not satisfied.
If the SQL command references an object that does not exist at
preprocessing time or if the individual doing the preprocessing is not
authorized to issue the command, the stored section is marked as invalid.
After being stored by the preprocessor, a valid section is marked as
invalid when such activities as the following occur:
* Change in authorities of the module's owner.
* Alteration to tables accessed by the program.
* Deletion or creation of indexes.
* Update of a table's statistics.
At run time, ALLBASE/SQL executes valid sections and attempts to validate
any section marked as invalid. If an invalid section can be validated,
as when an altered table does not affect the results of a query,
ALLBASE/SQL marks the section as valid and executes it. If an invalid
section cannot be validated, as when a table reference is invalid because
the table owner name has changed, ALLBASE/SQL returns an error indication
to the application program.
When a section is validated at run time, it remains in the valid state
until an event that invalidates it occurs. The program execution during
which validation occurs is slightly slower than program executions
following validation.