|
Problem IC87435
|
Status: Closed |
OPTIMIZER KEEPS UNNECESSARY COLUMNS AROUND AFTER PARTIAL GB OPERATION AND MIGHT RESULT IN POOR PERFORMANCE |
| product: |
DB2 FOR LUW / DB2FORLUW / A10 - DB2 |
| Problem description: |
In a partitioned database environment, the DB2 optimizer can
consider a group by (GB) alternative where the GB is partially
performed on each database partition, accumulating partial
results which are then re-distributed based on the grouping key
to complete the GB. For example, if a table T is hash
distributed across multiple database partitions based on column
X, then for the query
select a,max(b),min(c),sum(d)
from T
group by a
the GB cannot be completed locally at each partition since the
grouping key does not contain the hash distribution key. As a
result, a partial grouping result will be computed locally at
each database partition, with the partial aggregation results
and their source columns flowing through a table queue (TQ).
If these source columns are not required beyond the partial
result, width of the stream can be wider than is necessary which
can significantly degrade query execution performance. |
| Problem Summary: |
****************************************************************
* USERS AFFECTED: *
* The problem only occurs in a database partitioned *
* environment. *
****************************************************************
* PROBLEM DESCRIPTION: *
* See Error Description *
****************************************************************
* RECOMMENDATION: *
* Upgrade to DB2 version 10.1 Fix Pack 2. *
**************************************************************** |
| Local Fix: |
|
| available fix packs: |
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
|
| Solution |
The problem is first fixed in DB2 version 10.1 Fix Pack 2 |
| Workaround |
not known / see Local fix |
| Timestamps |
Date - problem reported :
Date - problem closed :
Date - last modified :
| 23.10.2012
15.04.2013
15.04.2013 |
| Problem solved at the following versions (IBM BugInfos) |
|
| Problem solved according to the fixlist(s) of the following version(s) |
| 10.1.0.2
|
 |
| 10.5.0.2
|
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