|
Problem IC84597
|
Status: Geschlossen |
DB2 SQL Optimizer might choose a suboptimal access plan for query with 'OPTIMIZE FOR N ROWS' clause and IS NULL predicate |
| Produkt: |
DB2 FOR LUW / DB2FORLUW / A10 - DB2 |
| Problembeschreibung: |
For a query with an 'optimize for N rows' clause and a highly
filtering IS NULL predicate, the DB2 SQL Optimizer might choose
a suboptimal query access plan as in the following example:
select *
from fact left outer join d1 on f1 = id1
left outer join d2 on f2 = id2
left outer join d3 on f3 = id3
left outer join d4 on f4 = id4
where d3.c31 is null;
with access plan graph for this query ( db2exfmt output ):
RETURN
|
>HSJOIN
/--------+---------\
>HSJOIN TBSCAN
/-------+-------\ |
>HSJOIN TBSCAN D4
/---+----\ |
FILTER TBSCAN D2
| |
>HSJOIN D1
/-----+------\
TBSCAN TBSCAN
| |
FACT D3
The IS NULL predicate is applied by the FILTER. The MAXPAGES
argument described in the details of the TBSCAN operator(s)
below the FILTER is a potential indicator of the problem. If
the MAXPAGES argument is small and the IS NULL predicate is
filtering many records, then a large amount of synchronous IO
might be required, resulting in suboptimal performance. |
| Problem-Zusammenfassung: |
****************************************************************
* USERS AFFECTED: *
* ALL *
****************************************************************
* PROBLEM DESCRIPTION: *
* See Error Description *
****************************************************************
* RECOMMENDATION: *
* Upgrade to DB2 version 10.1 Fix Pack 1 *
**************************************************************** |
| Local-Fix: |
|
| verfügbare FixPacks: |
DB2 Version 10.1 Fix Pack 1 for Linux, UNIX, and Windows
DB2 Version 10.1 Fix Pack 2 for Linux, UNIX, and Windows
DB2 Version 10.1 Fix Pack 3 for Linux, UNIX, and Windows
DB2 Version 10.1 Fix Pack 4 for Linux, UNIX, and Windows
DB2 Version 10.1 Fix Pack 3a for Linux, UNIX, and Windows
DB2 Version 10.1 Fix Pack 6 for Linux, UNIX, and Windows
|
| Lösung |
Problem was first fixed in DB2 version 10.1 Fix Pack 1 |
| Workaround |
keiner bekannt / siehe Local-Fix |
| Weitere Daten |
Datum - Problem gemeldet :
Datum - Problem geschlossen :
Datum - der letzten Änderung:
| 14.06.2012
31.10.2012
31.10.2012 |
| Problem behoben ab folgender Versionen (IBM BugInfos) |
|
| Problem behoben lt. FixList in der Version |
| 10.1.0.1
|
 |
| 10.5.0.1
|
|
