DB2 FOR LUW / DB2FORLUW / A50 - DB2

Using a high NUMDB setting (~100 or higher) may result 
in a hang or trap on DB2 / Linux.  The high setting results in 
the creation of an additional segment for the DBMS memory set 
during instance startup processing (db2start).  The address 
space assigned to the new segment for the db2sysc process at 
this point in time may not be available in the db2wdog 
(watchdog) process.  The watchdog may not then be able to 
function properly, resulting in unpredictable symptoms, 
including errors related to managing FMP processes. 
 
The db2ckpwd process handling authentication may also be 
impacted.  It may trap in sqltinit , resulting in hangs when 
attempting to connect to a database (or attach to an instance) 
with authentication. 
 
This problem may be more common in environments using address 
space layout randomization (ASLR). 
 
To confirm vulnerability, check "db2pd -memsets" whether a new 
segment is created immediately after db2start.  This record 
beginning with "Seg0" directly below the "DBMS" record indicates 
a new segment was added. 
 
Memory Sets: 
Name         Address            Id 
DBMS         0x0000000200000000 1314979889 
  Seg0       0x00002AAACD72A000 1315045427

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* USERS AFFECTED:                                              * 
* DB2 systems configured with a high NUMDB setting             * 
**************************************************************** 
* PROBLEM DESCRIPTION:                                         * 
* See Error Description                                        * 
**************************************************************** 
* RECOMMENDATION:                                              * 
* Upgrade to DB2 Version 10.5 Fix Pack 7                       * 
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Avoid unnecessarily large settings for the NUMDB database 
manager configuration parameter 
 
Updating the database manager configuration parameter 
MON_HEAP_SZ to its maximum size of 60000 (or "60000 AUTOMATIC") 
will also provide enough additional overhead in the DBMS set 
configuration to handle the requirements of the maximum NUMDBS 
setting (256).  This will avoid the creation of an additional 
segment during db2start and associated problem symptoms. 
 
   db2 update dbm cfg using MON_HEAP_SZ 60000 (add "AUTOMATIC" 
keyword if desired) 
   db2stop;db2start 
 
Note the higher MON_HEAP_SZ setting results in a higher instance 
memory reservation, but with the exception of Solaris - where 
ISM/pinned shared memory is used, it does not consume additional 
RAM on the system.

Problem first fixed in DB2 Version 10.5 Fix Pack 7

See Local Fix

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

07.01.2015
16.02.2016
16.02.2016