DB2 FOR LUW / DB2FORLUW / A50 - DB2

***** 
The Windows-specific symptoms have not been addressed by this 
APAR in versions 10.1, 10.5 (the version 9.7 APAR IT04320 does 
contain fixes for all symptoms).  Please see version 10.1 APAR 
IT21207 and version 10.5 APAR IT21209 for the complete fix. 
***** 
 
Two different symptoms may occur depending on the release of 
DB2. 
 
DB2 Version 9.7 Fix Pack 8 or higher 
1. Windows 64-bit systems on DB2 Version 9.7 Fix pack 8 or 
higher : 
Allocating memory may be 
significantly slower for databases with larger memory footprints 
( many GBs ).  Because DB2's memory allocations on Windows are 
typically small and incremental, coalesce checks end up being 
performed on a very large number of OS allocations.  Activities 
which are intense in terms of allocating memory (such as 
bufferpool activation, creation, or increase, or initializing 
LOAD operations), may suffer some degradation as a result 
 
 
2. DB2 on UNIX platforms, DB2 Version 10.1 Fix Pack 3 or higher, 
Version 10.5 GA or higher : 
On UNIX systems where DB2 allocates large amounts of shared 
memory, the problem impacts only larger allocations where a 
relatively large number of shared memory allocations exist for 
the memory area in question (say, > 100 shared memory segments) 
AND the memory allocation is failing at some level due to a 
limit (either in DB2 or the operating system). 
 
This situation is not typical.  Large single allocations are 
rare in shared memory, and typically there are only a few large 
shared memory allocations per memory area (for example, per 
database memory area).  The performance cost in this case is 
high per coalesce memory check and the overall duration of the 
large allocation, and the database may appear to be hung for 
short periods of time.  The allocation may fail in the end or 
the coalesce check may succeed - in either case the check will 
be expensive. 
 
The call stack for both of the above symptoms will contain the 
following : 
SMemSet::checkRecommitable 
SMemSet::recommitChunksUntilTargetReached 
SMemSet::getChunksFromTree 
SMemSet::getContiguousChunks 
SMemBasePool::getNewChunkSubgroup 
 
This APAR will alter coalesce checking to remove the excessive 
overhead for both of the above symptoms.

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* USERS AFFECTED:                                              * 
* All systems are vulnerable                                   * 
**************************************************************** 
* PROBLEM DESCRIPTION:                                         * 
* See Error Description                                        * 
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* RECOMMENDATION:                                              * 
* Upgrade to DB2 Version 10.5 Fix Pack 7                       * 
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Consider using 
   db2set DB2MEMDISCLAIM=NO 
followed by db2stop; db2start, which avoids the need for any 
coalesce check. 
 
Note that DB2MEMDISCLAIM=NO disables STMM-tuning of 
database_memory, though STMM will still tune the main consumers 
(bufferpools, locklist, package cache, shared sort) inside the 
existing database_memory size.

Problem first fixed in DB2 Version 10.5 Fix Pack 7

See Local Fix

Date  - problem reported    :
Date  - problem closed      :
Date  - last modified       :

16.01.2015
16.02.2016
27.06.2017