DB2 - Problembeschreibung
Problem IT27876 | Status: Geschlossen |
DB2 MAY COPY SELECTIVITY WHEN A SELECTIVITY CLAUSE IS USED ON A PREDICATE THAT'S COLUMN EQUIVALENT (C1=C2 AND C1=C3) | |
Produkt: | |
DB2 FOR LUW / DB2FORLUW / A50 - DB2 | |
Problembeschreibung: | |
This behavior may happen when the following conditions are met; - Registry variable DB2_SELECTIVITY has been set to YES - There are more than 1 equivalent predicates using the same column on the left so it's eligible for column equivalency Furthermore, DB2 may under-estimate cost when the following addditonal conditions are satisfied: - Registry variable DB2_CORRELATED_PREDICATES=FORCE_CGS. This is the default setting in 11.1Â - Column group statics are collected on the columns in the join equality predicates such that DB2 optimizer may adjust filter factor. To reproduce, create table t1(c1 int); create table t2(c1 int); create table t3(c1 int); And get a plan and check the optimized query; Original Statement: ------------------ select * from t1, t2, t3 where t1.c1=t2.c1 selectivity .12 and t1.c1=t3.c1 selectivity .13 Optimized Statement ------------------- SELECT T1.C1 AS "C1", T2.C1 AS "C1", T3.C1 AS "C1" FROM JINHYON1.T3 AS T3, JINHYON1.T2 AS T2, JINHYON1.T1 AS T1 WHERE (T1.C1 = T3.C1 SELECTIVITY 0.130000) AND (T3.C1 = T2.C1 SELECTIVITY 0.120000) The SELECTIVITY .12 is copied to T3.C1 = T2.C1 which is incorrect | |
Problem-Zusammenfassung: | |
**************************************************************** * USERS AFFECTED: * * ALL * **************************************************************** * PROBLEM DESCRIPTION: * * See Error Description * **************************************************************** * RECOMMENDATION: * * Will be fixed in DB2 v11.1. * **************************************************************** | |
Local-Fix: | |
N/A | |
Lösung | |
Workaround | |
keiner bekannt / siehe Local-Fix | |
Bug-Verfolgung | |
Vorgänger : IT27875 Nachfolger : | |
Weitere Daten | |
Datum - Problem gemeldet : Datum - Problem geschlossen : Datum - der letzten Änderung: | 24.01.2019 02.10.2020 02.10.2020 |
Problem behoben ab folgender Versionen (IBM BugInfos) | |
Problem behoben lt. FixList in der Version |