DB2 UDB for z/OS Version 8 Performance Topics - IBM Redbooks

Application programmers need to be able to make sure that SQL will perform correctly, but in
many cases they should not have the authority to read the actual data the SQL will be
selecting or updating, for example, sensitive payroll data. OWNER(SYSADM)
DYNAMICRULES(BIND) allows a user to EXPLAIN SQL statements without having the
privilege to execute those SQL statements. However, the drawback of this setting is that the
owner becomes the default qualifier for unqualified tables and views inside the SQL.
PTFs UQ92322 (DB2 V7) and UQ92323 (DB2 V8) for the two APARs PQ90022 and
PQ93821 add a new sample stored procedure called DSN8EXP that can be used to work
around these constraints. DSN8EXP accepts an SQL statement of up to 32700 single-byte
characters, passed as an input parameter from its caller. It first sets the current SQLID to
locate EXPLAIN tables, then it issues the EXPLAIN statement for the input SQL. You can
optionally let the stored procedure parse the SQL and add the qualifier ahead of those
unqualified tables/views if there are any unqualified tables/views in the SQL. For
insert-within-select and common table expressions, you need to disable the parsing function,
and add the qualifier manually. DSN8EXP returns the SQLCODE, SQLSTATE, and diagnostic
text from the EXPLAIN by output parameter.
Visual Explain for DB2 for z/OS Version 8 provides an easy-to-use interface to call the
DSN8EXP stored procedure.
Installation
This PTF also provides a new sample job called DSNTEJXP that you can use to prepare and
bind the DSN8EXP stored procedure. DSNTEJXP is not customized by the DB2 installation
CLIST. See the prolog of DSNTEJXP for guidance on customizing it to run at your site.
Running DSN8EXP from Visual Explain
In the Subsystem Parameters Panel there are fields to specify the stored procedure's schema
name and procedure name. When all necessary fields are filled in the TuneSQL panel, note
there is a field called "Table qualifier for Explain stored procedure:" When this field has a
non-blank value, it is used as the input parameter QUALIFIER for the stored procedure and
the parsing function will be enabled; if this field is blank, then the parsing is disabled. There is
also a button called "Explain with stored procedure" shown in the TuneSQL panel, which
actually invokes the EXPLAIN stored procedure. The original EXPLAIN button still issues
normal Explain statements.
5.6.9 PLAN_TABLE access via a DB2 alias
Up to V7, you did not have the capability to access Explain tables with different OWNER and
QUALIFIER names. OWNER refers to the creator of the EXPLAIN table; QUALIFIER refers to
the user that issues the EXPLAIN statement. A limitation of the EXPLAIN command has been
that only the owner of the EXPLAIN tables can issue the EXPLAIN statement to populate
his/her tables. This has prevented you from being able to consolidate your plan tables under a
single AUTHID.
Starting with V8, you can use the ALIAS mechanism to populate EXPLAIN tables created
under a different AUTHID. The following external EXPLAIN tables can now have aliases
defined on them:
► PLAN_TABLE
► DSN_STATEMNT_TABLE
► DSN_FUNCTION_TABLE
The alias name must have the format userid.table_name where tablename can be
PLAN_TABLE, DSN_STATEMNT_TABLE or DSN_FUNCTION_TABLE.
Chapter 5. Availability and capacity enhancements 259