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

– DATASPACE BP CONTROL BLOCKS = 0 MB (data spaces are not used here)
– DATASPACE LOOKASIDE BUFFER = 0 MB
In our example, buffer pools and control structures use a total of 451.17 MB, which represents
almost 58% of the total DBM1 storage.
Besides the virtual storage required for the buffer pools, other components can be large
consumers of virtual storage in the DBM1 address space depending on the workload and
system parameter settings:
► The EDM pool containing active and skeleton plans and packages, dynamic statements,
and Database Descriptors (DBDs). The maximum size is specified by the system
parameter EDMPOOL in DSNZPARM. The storage used is shown by the following
indicator:
– EDM POOL = 146.48 MB
► Compression dictionaries can also consume significant amounts of storage in the DBM1
address space, especially when a compression dictionary is required for every partition of
a partitioned table space. The compression dictionary for each table space/partition that is
opened. The size of a compression dictionary is 64 KB. The storage required is shown by
the following indicator:
– COMPRESSION DICTIONARY = 0 MB (compression is not used here)
► DB2 allocates Castout buffers only in a data sharing environment. Castout buffers are
used by DB2 to read changed pages from the GBP into the DBM1 address space, as a
part of writing them out to disk. Since 128 KB are allocated per castout engine, and you
can have up to 600 castout engines, the total can be up to 77 MB of storage.
– CASTOUT BUFFERS = 0.00 MB (data sharing is not used)
Variable pools
The TOTAL VARIABLE STORAGE contains storage used by threads or agents as working
storage, RID pool, RDS OP pool, Pipe manager subpool (working storage pools used by
parallel tasks), local dynamic statement cache control blocks, thread copies of cached SQL
statements (each thread’s Local Dynamic Statement Cache) and storage for various trace
tables. Agent storage is further itemized into storage for “system agents” (such as prefetch
engines, deferred write engines, castout engines, GBP write engines, P Lock exit engines)
and “non-system agents”, which includes the number of all active allied threads and active
DBAT threads.
► TOTAL AGENT LOCAL STORAGE = 109.16 MB combines both TOTAL AGENT SYSTEM
STORAGE and TOTAL AGENT NON-SYSTEM STORAGE.
► TOTAL AGENT SYSTEM STORAGE = 3.54 MB. This is the total storage consumed in the
variable pools by the various system agents (for example, prefetch engines, deferred write
engines, and castout engines).
► TOTAL AGENT NON-SYSTEM STORAGE = 105.63 MB. This is the total storage
consumed in the variable pools by all the active threads. The normal range for DB2 V8 is
200 KB to 10 MB per thread. Simple threads like CICS transactions can be as low as 200
KB while SAP threads can be as much as 10 MB per thread.
► RID POOL = 0.57 MB. This is the total storage consumed in the variable pools for the RID
pool. The RID pool is used for list prefetch, multiple index access processing, and hybrid
joins. The maximum size is specified by the DSNZPARM parameter MAXRBLK.
► The Local Dynamic Statement Cache size is indirectly determined by the DSNZPARM
parameter MAXKEEPD when KEEPDYNAMIC(YES) is used. The storage used in the
virtual pools is shown by the following indicators:
160 DB2 UDB for z/OS Version 8 Performance Topics