Download DB2 LUW Automatic Memory Management Configuration Tips

769818018
There are DB2 LUW configuration parameters that can be set to AUTOMATIC and managed by
the DB2 automatic memory manager (STMM). One advantage of this is that DB2 will
automatically adjust the memory it uses to get the work done based on the characteristics
of the current work load and it will continue to adjust itself dynamically as processing
continues.
Below is a list of configuration parameters for DB2 V9.5 that can be set to
AUTOMATIC.
Here is a list of database manager (instance) configuration values for a partitioned
environment that can be set to AUTOMATIC. Note that the SHEAPTHRES can be set to 0 and
this combined with other database level configuration parameters can result in DB2 sort
memory being managed by the automatic memory manager.
db2 attach to db2inst1
db2 get dbm cfg show detail
Database monitor heap size (4KB)
(MON_HEAP_SZ)
Size of instance shared memory (4KB) (INSTANCE_MEMORY)
Agent pool size
(NUM_POOLAGENTS)
Max number of coordinating agents
(MAX_COORDAGENTS)
Max number of client connections
(MAX_CONNECTIONS)
Number of pooled fenced processes
(FENCED_POOL)
No. of int. communication buffers(4KB)(FCM_NUM_BUFFERS)
No. of int. communication channels
(FCM_NUM_CHANNELS)
Sort heap threshold (4KB)
(SHEAPTHRES)
=
=
=
=
=
=
=
=
=
AUTOMATIC(4096)
AUTOMATIC(889708)
AUTOMATIC(0)
AUTOMATIC(2000)
AUTOMATIC(MAX_COORDAGENTS)
AUTOMATIC(MAX_COORDAGENTS)
AUTOMATIC(4096)
AUTOMATIC(2048)
0
Here is a list of database configuration values that can be set to AUTOMATIC. Note that
the CATALOGCACHE_SZ may be set to -1 and that this results in it’s memory size being
derived by the formula (MAXAPPLS*4). If MAXAPPLS is set to AUTOMATIC then the databases
catalog cache memory size is indirectly managed by DB2’s automatic memory manager.
db2 connect to db2db1
db2 get db cfg for db2db1
Size of database shared memory (4KB) (DATABASE_MEMORY)
Max storage for lock list (4KB)
(LOCKLIST)
Percent. of lock lists per application
(MAXLOCKS)
Package cache size (4KB)
(PCKCACHESZ)
Sort heap thres for shared sorts (4KB) (SHEAPTHRES_SHR)
Sort list heap (4KB)
(SORTHEAP)
Database heap (4KB)
(DBHEAP)
SQL statement heap (4KB)
(STMTHEAP)
Default application heap (4KB)
(APPLHEAPSZ)
Application Memory Size (4KB)
(APPL_MEMORY)
Statistics heap size (4KB)
(STAT_HEAP_SZ)
Number of asynchronous page cleaners
(NUM_IOCLEANERS)
Number of I/O servers
(NUM_IOSERVERS)
Default prefetch size (pages)
(DFT_PREFETCH_SZ)
Max number of active applications
(MAXAPPLS)
Average number of active applications
(AVG_APPLS)
Catalog cache size (4KB)
(CATALOGCACHE_SZ)
=
=
=
=
=
=
=
=
=
=
=
=
=
=
=
=
=
CALCULATED
AUTOMATIC(12097)
AUTOMATIC(98)
AUTOMATIC(3465)
AUTOMATIC(152076)
AUTOMATIC(3041)
AUTOMATIC(20000)
AUTOMATIC(4096)
AUTOMATIC(2000)
AUTOMATIC(6928)
AUTOMATIC(6600)
AUTOMATIC(1)
AUTOMATIC(18)
AUTOMATIC
AUTOMATIC(430)
AUTOMATIC(1)
(MAXAPPLS*4)
Change self tuning memory to off and STMM is off. If you do not change the configuration
values then they are set to the last value STMM used.
Self tuning memory
Composed by Mark Mulligan
(SELF_TUNING_MEM) = ON (Active)
Page 1 of 3
4/29/2017 9:57:00 PM
769818018
LINUX Configuration Tip: If you want to use the DB2 LUW Automatic Memory Manager feature
on a LINUX server then the maximum segment size (SHMMAX) should be configured to the same
size as the maximum total shared memory (SHMALL) and the maximum total shared memory
(SHMALL) should be configured to the total physical memory on the server.
DB2 Configuration Tip: If the maximum segment size is less than the maximum total shared
memory for LINUX then you should avoid using AUTOMATIC on configuration parameters that
manage the amount of shared memory that DB2 will use or you will experience problems if
DB2 exceeds these limits. The same is true for the maximum total shared memory if it is
set to something smaller than the maximum physical memory on the server. The SHMMAX and
SHMALL LINUX configuration values limit the amount of shared memory DB2 can use on a
LINUX server. If DB2 is configured to exceed these limits or if the DB2 automatic memory
manager adjusts DB2 shared memory so that it exceeds these limits then LINUX will stop
the DB2 threads when these limits are exceeded.
Here is the formula to use when configuring DB2 to run within the max segment memory size
of an operating system like LINUX.
(util_heap_sz * 4096) +
(dbheap * 4096) +
(catalogcache_sz * 4096) +
(locklist * 4096) +
(pckcachesz * 4096) +
(bufferpool_1 * bufferpool_page_size) +
(bufferpool_n * bufferpool_page_size)
<= LINUX maximum segment size (SHMMAX)
You can determine the current values of the DB2 database utility heap size, database
heap, catalog cache, lock list and package cache by connecting to the database and
running the db2 get database configuration command with the show detail option.
db2 connect to db2db1
db2 get db cfg for db2db1 show detail
You can determine the current values for the DB2 bufferpools in a database by running the
SQL select statement listed below. If you see a -2 value then the bufferpool is
configured to have it’s memory managed by DB2’s automatic memory manager. Note, that
size in bytes of memory for a bufferpool may be calculated by multiplying page size times
the number of pages (PAGESIZE * NPAGES).
db2 -v "select substr(bpname,1,15) as bpname,pagesize,npages from syscat.bufferpools
order by bpname"
select substr(bpname,1,15) as bpname,pagesize,npages from syscat.bufferpools order by
bpname
BPNAME
PAGESIZE
NPAGES
--------------- ----------- ----------BPTBL32K
32768
40960
BPTMP04K
4096
1000
BPTMP08K
8192
1000
BPTMP16K
16384
1000
BPTMP32K
32768
4395
IBMDEFAULTBP
16384
19000
Composed by Mark Mulligan
Page 2 of 3
4/29/2017 9:57:00 PM
769818018
In order to determine how a LINUX server is configured run the command ipcs –l.
------ Shared Memory Limits -------max number of segments = 4096
max seg size (kbytes) = 262144
max total shared memory (kbytes) = 8388608
min seg size (bytes) = 1
SHMMAX
SHMALL
------ Semaphore Limits -------max number of arrays = 1024
max semaphores per array = 250
max semaphores system wide = 32000
max ops per semop call = 32
semaphore max value = 32767
------ Messages: Limits -------max queues system wide = 1024
max size of message (bytes) = 65535
default max size of queue (bytes) = 65536
If you multiply the SHMMAX size times 1024 (Kbytes) then you will have the number of
bytes available for a segment on the LINUX server. If this matches the SHMALL value and
if the SHMALL value matches the total physical memory on the server then you are free to
use AUTOMATIC for DB2 LUW database configuration values for utility heap size, database
heap, catalog cache, lock list, package cache and bufferpools. If SHMMAX is less than
SHMALL or if SHMALL is less than the physical memory available on the LINUX server then
you should configure utility heap size, database heap, catalog cache, lock list, package
cache and bufferpools so that the total bytes of shared memory they use is equal to or
less than the LINUX segment maximum limit of shared memory limit, which ever is smaller.
You can set up a spreadsheet with formulas that will help you make sure that your DB2 LUW
database configuration and bufferpool configuration will be equal to or less than the max
seg size limit on the LINUX server. Here is an example of one way you could do this.
ipcs -l command
Shared Memory Limits
max number of segments
max seg size (kbytes)
max total shared memory (kbytes)
min seg size (bytes)
Semaphore Limits
max number of arrays
max semaphores per array
max semaphores system wide
max ops per semop call
semaphore max value
Messages: Limits
max queues system wide
max size of messages (bytes)
default max size of queue (bytes)
Composed by Mark Mulligan
Value
Measure
Bytes
4,096
262,144
8,388,608
1,024
250
32,000
32
32,768
1024
1024
268,435,456
8,589,934,592 util_heap_sz
1 dbheap
catalogcache_sz
locklist
pckcachesz
BUF32K
BUFF8K
IBMDEFAULTBP
DB2 Shared memory
Current
Configuration
5000
1200
384
1500
512
1500
1000
90000
1,024
65,535
65,536
Page 3 of 3
4/29/2017 9:57:00 PM
Page
Size
4,096
4,096
4,096
4,096
4,096
32,768
8,193
4,096
Bytes
20,480,000
4,915,200
1,572,864
6,144,000
2,097,152
49,152,000
8,193,000
368,640,000
461,194,216
Propos
5,0
1,2
3
1,5
5
1,5
1,0
42,9