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MA47191 - LIC-DB-OTHER-PERFM PESSIMISTIC INDEX SCAN COSTING IS INFLATING *CS STACKED TABLE PROBE NODE COST

 APAR (Authorized Program Analysis Report)

Abstract

LIC-DB-OTHER-PERFM PESSIMISTIC INDEX SCAN COSTING IS INFLATING
*CS STACKED TABLE PROBE NODE COST

Error Description

DB2Connect (QRWTSRVR / failing) had extremely long processing  
time to return results. Exact same query from Run SQL Scripts  
(QZDASOINIT) works just fine.                                  
Under some circumstances, including the use a commit control    
level of *CS (Cursor Stability), queries that specify ordering  
may run slowly. The optimizer may overestimate the cost of an  
access plan that uses an index scan to provide ordering and may
choose a less efficient ordering method.                        

Problem Summary

Please see the ERROR DESCRIPTION section.                      

Problem Conclusion

The optimizer was using pessimistic costing in situations in    
which it was not appropriate. The optimizer logic has been      
improved to avoid using pessimistic costing for these          
situations.                                                    

Temporary Fix

Comments

Circumvention


PTFs Available

R720 MF65210   9123
R730 MF65174   9116

Affected Modules

         
         

Affected Publications

Summary Information

Status............................................ CLOSED PER
HIPER........................................... Yes
Component.................................. 9400DG3DB
Failing Module.......................... RCHMGR
Reported Release................... R730
Duplicate Of..............................




System i Support

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Document information

More support for: i family

Software version: V7R2M0, V7R3M0

Operating system(s): OS/400

Reference #: MA47191

Modified date: 17 May 2019