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DB2 - Problem description

Problem IC78091 Status: Closed

DB2 INCORRECTLY RELEASES SHARED MEMORY ON LINUX, LEADING TO PAGING,
PERFORMANCE DEGRADATION

product:
DB2 FOR LUW / DB2FORLUW / 950 - DB2
Problem description:
DB2 is intending to use the MADV_REMOVE flag on Linux to 
decommit memory with the madvise() API, but instead is falling 
back to a weaker MADV_DONTNEED flag.  This is due to an 
incorrect attempt to use MADV_REMOVE with memory mapped stack 
memory. 
 
As a result, DB2's shared memory is not being decommitted, but 
only unmapped.  Memory is not being released dynamically by DB2 
as expected and is also highly eligible for paging out, which 
can later result in performance degradation on page-ins if DB2 
wants to reuse the memory.  STMM will also not account for this 
memory in its target calculations, since it appears in memory 
statistics as though it were clean file cache pages, and 
available for other use.  This leads to memory overcommitment in 
STMM-tuned environments. 
 
Please note that vm.swappiness should be set to 0 for DB2 
systems, otherwise this may result in system swapping when there 
is no memory overcommitment.
Problem Summary:
**************************************************************** 
* USERS AFFECTED:                                              * 
* DB2 LUW on Linux platform                                    * 
**************************************************************** 
* PROBLEM DESCRIPTION:                                         * 
* See Error Description                                        * 
**************************************************************** 
* RECOMMENDATION:                                              * 
* Upgrade to DB2 Version 9.5 Fix Pack 9                        * 
****************************************************************
Local Fix:
available fix packs:
DB2 Version 9.5 Fix Pack 9 for Linux, UNIX, and Windows
DB2 Version 9.5 Fix Pack 10 for Linux, UNIX, and Windows

Solution
Problem first fixed in DB2 Version 9.5 Fix Pack 9
Workaround
not known / see Local fix
Timestamps
Date  - problem reported    :
Date  - problem closed      :
Date  - last modified       :
11.08.2011
12.06.2012
12.06.2012
Problem solved at the following versions (IBM BugInfos)
9.5.FP9
Problem solved according to the fixlist(s) of the following version(s)
9.5.0.9 FixList
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