DB2 UDB for z/OS Version 8 Performance Topics - IBM Redbooks

= MVS EXTENDED REGION SIZE (MAX) - MVS 31 BIT EXTENDED LOW PRIVATE
or
1628.00 - 24.64 = 1603.36 MB
► C is the basic cushion constant of 200 MB.
► F is the value for fixed areas
or
= TOTAL GETMAINED STORAGE + TOTAL GETMAINED STACK STORAGE + TOTAL FIXED STORAGE
599.18 + 26.77 + 0.30 = 626.25 MB
The maximum theoretical number of threads can therefore be estimated as:
V/TF
For our example, the theoretical maximum number of threads can be estimated as:
(1603.36 - 200 - 626,25) / 0.3 = 777.11 / 0.30 = 2590.37.
This is also reported in the report as MAX NUMBER OF POSSIBLE THREADS as 2593.01.
The difference between 2590 and 2593 can be explained because the above calculation is
based on the rounded MB values of the report, while Performance Expert uses the exact byte
values of IFCID 225.
Be warned that this is a maximum theoretical limit and should only be used as a guide or
rough estimate. It does not provide for things such as growth in buffer pools and more
compression dictionaries that may be required to support the extra workload.
The stack storage size is directly proportional to the number of threads, not FIXED. Even
Getmained ones are really not fixed. Threads would typically be much bigger in an
environment which has many more threads. If a measurement run has 100 threads and the
maximum is calculated much higher for the projection, such as 1000, the result in the
maximum number of threads allowed tends to be much higher than really possible.
So, what has changed in DB2 V8?
Example 4-2 shows the same extract from a DB2 PE V8.1 Statistics Long Trace, but this time
it shows the DBM1 STORAGE STATISTICS section for a DB2 V8 subsystem. Once again, the
report was produced with the fix for APAR PQ91101 applied to DB2 and the fix for APAR
PQ94872 applied to DB2 PE.
Example 4-2 DBM1 Storage Statistics for a DB2 Version 8 subsystem
DBM1 AND MVS STORAGE BELOW 2 GB QUANTITY DBM1 AND MVS STORAGE BELOW 2 GB CONTINUED QUANTITY
-------------------------------------------- ------------------ -------------------------------------------- ------------------
TOTAL DBM1 STORAGE BELOW 2 GB (MB) 539.30 24 BIT LOW PRIVATE (MB) 0.21
TOTAL GETMAINED STORAGE (MB) 236.09 24 BIT HIGH PRIVATE (MB) 0.43
VIRTUAL BUFFER POOLS (MB) N/A 31 BIT EXTENDED LOW PRIVATE (MB) 30.45
VIRTUAL POOL CONTROL BLOCKS (MB) N/A 31 BIT EXTENDED HIGH PRIVATE (MB) 553.99
EDM POOL (MB) 234.38 EXTENDED REGION SIZE (MAX) (MB) 1628.00
COMPRESSION DICTIONARY (MB) N/A EXTENDED CSA SIZE (MB) 256.83
CASTOUT BUFFERS (MB) N/A
DATA SPACE LOOKASIDE BUFFER (MB) N/A AVERAGE THREAD FOOTPRINT (MB) 0.46
HIPERPOOL CONTROL BLOCKS (MB) N/A MAX NUMBER OF POSSIBLE THREADS 2377.81
DATA SPACE BP CONTROL BLOCKS (MB) N/A
TOTAL VARIABLE STORAGE (MB) 231.47
TOTAL AGENT LOCAL STORAGE (MB) 195.72
TOTAL AGENT SYSTEM STORAGE (MB) 2.32
NUMBER OF PREFETCH ENGINES 6
NUMBER OF DEFERRED WRITE ENGINES 10
NUMBER OF CASTOUT ENGINES 0
NUMBER OF GBP WRITE ENGINES 0
NUMBER OF P-LOCK/NOTIFY EXIT ENGINES 0
TOTAL AGENT NON-SYSTEM STORAGE (MB) 193.40
TOTAL NUMBER OF ACTIVE USER THREADS 500
Chapter 4. DB2 subsystem performance 163