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

C.1 DB2 SQL PA additional reports
Notice that the index used has a NOT PADDED attribute and a cartesian join was detected.
Example C-1 reports the query definition and also some good news for the query.
Example: C-1 SQL PA query description
================================================================================
SQL PA ANALYSIS FOR QUERYNO 100000001
SELECT COUNT(*) FROM
SYSIBM.SYSPACKSTMT A, SYSIBM.SYSPACKDEP B
WHERE A.LOCATION = ? AND
B.DLOCATION = ? AND
B.DCOLLID = ? AND
A.COLLID ?
QUERYNO: 100000001 QBLOCKNO: 1 PLANNO: 1 MIXOPSEQ: 0
PROCESS ->
+------------------------------------------------------------------+
|ANL7002I *** GUIDELINE: |
|This plan step has not selected any Sequential|List Prefetch I/O. |
|If the SQL processes just a few rows that is OK, but if many rows |
|are involved, you can help promote Sequential Detection by both |
|accessing the data in sequential order (presort?) and by binding |
|with Release (Deallocate) to avoid resetting counters at Commit. |
+------------------------------------------------------------------+
+------------------------------------------------------------------+
|ANL7005I *** GOOD NEWS: |
|This SQL features a Unique Index being used to access the table |
|that can avoid Distinct Sorts with Group By and Count Distinct C1.|
|Also, unique index will avoid 4K "in memory table" on Correlated |
|Subquery, considers special access path when used with "=" preds, |
|and may convert Subquery to Join on IN, =ANY or =SOME predicates. |
+------------------------------------------------------------------+
+------------------------------------------------------------------+
|ANL6005I *** NOTE: |
|This statement contains a Built in Column Function: however, it |
|is not being processed at either Stage 1 Retrieval or Sort Time. |
|In general, this means poor performance, because the column(s) get|
|evaluated only at the end of Stage 2 processing. This might be due|
|to multiple columns used, Group By, not all Stage 1 preds, etc. |
+------------------------------------------------------------------+
Example C-2 provides information about the indexes.
Example: C-2 SQL PA index information
ACCESS IS VIA THE CLUSTERING (INSERT & LOAD ORDER) INDEX FOR THIS TABLE
+------------------------------------------------------------------+
|ANL5018W *** ALERT: |
400 DB2 UDB for z/OS Version 8 Performance Topics