|
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
|
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