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

Column Type Content
VIEW_NAME VARCHAR(128) NOT NULL WITH
DEFAULT
PATH VARCHAR(2048) NOT NULL WITH
DEFAULT
FUNCTION_TEXT VARCHAR(1500) NOT NULL WITH
DEFAULT
D.1.4 DSN_STATEMNT_CACHE_TABLE
This new table was recently introduced by PTF UQ89372 for APAR PQ88073. With this
enhancement a new keyword ALL is added to EXPLAIN STMTCACHE and a new explain
table DSN_STATEMENT_CACHE_TABLE is created to hold the output of IFCID 316 and
IFCID 318.
A brief description follows, as reported in the APAR text.
There are two different sets of information that can be collected from the SQL statements in
the dynamic statement cache. Specifying STMTCACHE with the STMTID or STMTTOKEN
keywords causes the traditional access path information to be written to the PLAN_TABLE for
the associated SQL statement as well as a single row written to
DSN_STATEMENT_CACHE_TABLE if it exists.
However, specifying STMTCACHE with the new ALL keyword causes information to be
written to only DSN_STATEMENT_CACHE_TABLE. It consists of one row per SQL statement
in the dynamic statement cache for which the current authorization ID is authorized to
execute.
The contents of these rows show identifying information about the cache entries, as well as
an accumulation of statistics reflecting the executions of the statements by all processes that
have executed the statement.
This information is nearly identical to the information returned from the IFI monitor READS
API for IFCIDs 0316 and 0317.
Note that the collection and reset of the statistics in these records is controlled by starting and
stopping IFCID 318. For more details, see "Controlling collection of dynamic statement cache
statistics with IFCID 0318" in DB2 UDB for z/OS Version 8 Administration Guide,
SC18-7413-01, Appendix E - Programming for the Instrumentation Facility Interface (IFI).
The new EXPLAIN option is:
EXPLAIN STMTCACHE ALL;
The name of the view, if the function
that is specified in the
FUNCTION_NAME column is
referenced in a view definition.
Otherwise, this field is blank.
The value of the SQL path when DB2
resolved the function reference.
The text of the function reference (the
function name and parameters).
SQLCODE -20248 is issued if no statement is found in the cache for the auth ID that is used.
-20248 ATTEMPTED TO EXPLAIN A CACHED STATEMENT WITH
STMTID, STMTTOKEN ID-token, OR ALL BUT THE REQUIRED
EXPLAIN INFORMATION IS NOT ACCESSIBLE.
Before you can use EXPLAIN STMTCACHE ALL, Statement Cache must be turned on. You
must also create the table DSN_STATEMENT_CACHE_TABLE to hold the results of
EXPLAIN STMTCACHE ALL. The DDL is shown in Example D-1.
Appendix D. EXPLAIN and its tables 417