3729638 - DB6: db2diag.log - DIA8300C A memory heap error has occurred - What to Check/Collect for SAP.

The db2diag.log reports warnings that the OOM - Instance memory request failed. In the following example, it shows errors/warnings which follow the DIA8300C A memory heap error has occurred. 
With STMM (Self Tuning Memory Management) set to ON, Db2 tries to expand a memory heap and fails when the request is more than the available memory limit. This may not be an error but a warning that memory is reaching it's limit.

EXAMPLE:

Below we see that the INSTANCE_MEMORY request failed.  The controller metrics show that MEMORY is at it's fullest peak with no available memory which 
results in the error SQLO_NOMEM "No Memory Available". The area where the out of memory failure occurs is the Application Heap (APPLHEAPSZ)on node 0.
It is not clear what is causing the issue until further investigation is carried out. 

2026-03-10-08.14.57   LEVEL: Warning
PID     : XXXXX       TID : XXXXXXXXXXXXXXXX PROC : db2sysc 0
INSTANCE: db2xxx      NODE : 000            DB   : XXX
APPHDL  : XXXXXXX     APPID: XXXXXXXXXXXXXXXXXXXXXXXXX
UOWID   : XXXX        ACTID: XX
AUTHID  : SAPXXX      HOSTNAME: XXXXXXXX
EDUID   : XXXX        EDUNAME: db2agntcol 
FUNCTION: DB2 UDB, SQO Memory Management, SqloMemController::requestMemory, probe:50
MESSAGE : ZRC=0x8B0F0000=-1961951232=SQLO_NOMEM "No Memory Available"
          DIA8300C A memory heap error has occurred.
DATA #1 : String, 36 bytes
OOM - Instance memory request failed

==>>>

The values are broken down in accordance to allocation request.
DATA #3 : unsigned integer, 8 bytes
1048576 <===== This is the amount Db2 is requesting,(Generally in 4K pages).
DATA #4 : unsigned integer, 8 bytes
0
DATA #5 : String, 13 bytes
APPL-<SID> <====This is the consumer,(The memory that STMM is trying to expand). In this example it is application heap. Other examples include the name of the database for the Database heap, or Private for the Instance Private Memory.     
DATA #6 : unsigned integer, 8 bytes
43564924928   <== Total memory for the heap being used,(4K pages).
DATA #7 : unsigned integer, 8 bytes
0
DATA #8 : unsigned integer, 8 bytes
187904098304  <==== The current value in use overall in KB
DATA #9 : unsigned integer, 8 bytes
187904819200 <=== The INSTANCE_MEMORY in KB rather than 4KB pages (Data #2 + Data #7 cannot exceed this value)
DATA #10: unsigned integer, 8 bytes
0

The db2diag.log should also reference the memory in use.  Check the db2diag.log for 
Instance Memory Controller statistics.
Instance Memory Automatic: No.
Maximum size = <value> KB
Current size = <value> KB 
Usage HWM    = <value> KB 
Cached memory = 0 KB
Cached DB memory = 0 KB

2026-03-10-08.14.57   LEVEL: Error
PID     : XXXXX       TID : XXXXXXXXXXXXXXXX PROC : db2sysc 0
INSTANCE: db2xxx      NODE : 000            DB   : XXX
APPHDL  : XXXXXXX     APPID: XXXXXXXXXXXXXXXXXXXXXXXXX
UOWID   : XXXX        ACTID: XX
AUTHID  : SAPXXX      HOSTNAME: XXXXXXXX
EDUID   : XXXX        EDUNAME: db2agent
FUNCTION: DB2 UDB, WLM, sqlrwGetPkgCacheStmtMetrics, probe:20
MESSAGE : ZRC=0x8B0F0000=-1961951232=SQLO_NOMEM "No Memory Available"
          DIA8300C A memory heap error has occurred.

2026-03-10-08.14.57  LEVEL: Warning
PID     : XXXXX      TID : XXXXXXXXXXXXXXXX PROC : db2sysc 0
INSTANCE: db2xxx     NODE : 000            DB   : XXX
APPHDL  : XXXXXXX    APPID: XXXXXXXXXXXXXXXXXXXXXXXXX
UOWID   : XXXX       ACTID: XX
AUTHID  : SAPXXX     HOSTNAME: XXXXXXXX
EDUID   : XXXX       EDUNAME: db2agntcol

FUNCTION: DB2 UDB, SQO Memory Management, sqloMemLogPoolConditions, probe:30
DATA #1 : <preformatted>
Out of memory failure for Application Heap (APPLHEAPSZ) on node 0.  

db2 LUW IBM

memory heap allocation, APPLHEAPSZ, APPL_MEMORY, memory tuning, IBM , KBA , BC-DB-DB6 , DB2 Universal Database for Unix / NT , Bug Filed