)
)
QCR and Message Buffer Pool. One queue control record buffer is required for each input 2740 and one for each 1050 telecommunication line to be serviced. step 4 of stage 2 of IMS/360 system definition adds the procedure to the user-defined procedure library named IMSO.
The calculated number of QCR buffers required is defined in the DOD positions of the PARM= operand on the EXEC card. In that procedure, a number of message buffers are defined in the EEE positions of the PARM=
operand for the system defined by the user. Message buffers are utilized for handling multiline messages.
The main storage requirements for these buffers may be determined by using the following sizes per buffer:
Queue control record buffer 176 bytes
One QCR buffer is required for each input communication line and each message region.
Message buffer 880 bytes
One message buffer is required for each simultaneous input or output request for a multisegment message.
Data Base Buffer Pool. When a program is scheduled into a message
region or when a Type 2 batch program is scheduled" the buffers required for the data bases used by that program are obtained from a general data base buffer pool. When the application program terminates., the assigned buffers are returned to the pool. The output of each DBD generation Step 2 (linkage editor) includes a SETSSI value produced in Step 1.
This value is the data base buffer byte requirement in hexadecimal required for use of the data base
byan application program in an IMS/360 Type 1 or 2 region. If data base logging is specified for any data base referenced by a message or batch Type 2 program, the size of a message buffer (80 bytes) plus 72 bytes (152 bytes total) must be added to the total buffer requirements for that program. The pool of data base buffers provided for use in the IMS/360 Type 0 region must be at least as large as that required by the message program or batch program in a Type 2 region which uses the largest number of data base buffer bytes. As an example, assume that program X, the largest user of data base buffers" uses three data bases which require 5000 bytes of buffer storage each. The absolute minimum requirement for the data base buffer pool will be 15,000 bytes. If more than one Type 1 or 2 region is to execute concurrently, the data base buffer pool must be large enough to obtain the buffers £or the data bases to be used in each message and Type 2 region concurrently.. If the data base buffer requirement
associated with an application program cannot be satisfied at the time the program is to be scheduled for execution, IMS/360 will wait until buffer space becomes available. The IMSO procedure provides a default size for the data base buffer pool in the HHH positions of the PARM=
operand of the EXEC card.
In addition to data base buffers, space in this pool is used to
supply buffers during a /DBDUMP execution. These additional buffers are used for the HSAM data base image of the HISAM data base to be dumped.
The total buffer space requirement is equal to twice the buffer requirement for the largest data base to be dumped.
2740/1050 Output Line Buffer Pool. Output messages to be transmitted via communication lines are read from queue control record and message buffers, edited to include line control characters, translated., and placed in output line buffers. Output line buffers are contained in the output line buffer pool. The size of this pool is defined by the HHH positions of the PARM= operand of the EXEC card in the IMSO procedure .•
The value specified for the
HHHpositions of the PARM= operand should
include the output line buffer pool requirements in addition to the data
base buffer pool requirements. A reasonable pool size requirement might
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be 200 bytes per buffer and one buffer per three output 2740/1050I communication lines. Howeverr if response is inadequate, the number of buffers should be increased.
2260 Line Buffer Pool. Buffers required for communication line control operations with a 2260 terminal are obtained from the 2260 line buffer pool. The size of this pool is defined by the HHH positions of the PARM= operand of the EXEC card in the IMSO procedure. The value
'specified for the HHH positions of the PARM= operand should include the
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2260 line buffer pool requirements in addition to the 1050/2740 output line buffer and data base buffer pools. One puffer of 1000 bytes should be included for each active 2260 line.PSB and DMB Pool Sizes. A control block called a PSB exists on the PSB library for each message or batch Type 2 program. This block is loaded into core storage when the program is scheduled, and is retained as long as possible. The PSB is maintained in the PSB pool. A control block called the DBD also exists on the DBD library for each data base. This block is loaded into core storage and modified to create a DMB when the data base is initially used. The DMB is retained' as long as possible in the DMB pool. The DMB contains DCB"s for the data base in an OPEN
state. The ability of IMS/360 to retain PSB's and DMB"s in core depends upon their respective pool sizes.
The sizes of the PSB and DMB pools are determined by the values specified in the FFF and GGG positions of the IMSO procedure PARM=
operand. A default value is assigned by IMS/360 system definition to the FFF and GGG positions of the IMSO procedurePARM= operand. These values must be at least large enough to contain the largest PSB as expanded during loading and all DMB's required by the application program that uses the largest number of data bases.
The size of a typical PSB is 500 to 1000 bytes. The size of a
typical DMB is 600 bytes per data set group in the data base. The more PSB's and DMB's that remain resident, the greater the performance of the IMS/360 system. The maintenance of PSB's and DMB's in their respective pools is based upon frequency of use. The more often a program is scheduled and its data bases accessed, the greater the probability of retention of the block in core storage. The user can retain all PSB's and DMB's in core if the pools are defined large enough.
When a PSB is removed from the PSB pool to accommodate a new PSB, all DMB's used by that PSB and not concurrently used by other PSB"s at time of PSB removal are removed from the DMB pool. This means the closing of the associated data sets. The user may avoid the removal of HISAM DMB's through the use of the second position in the PARM= operand on the EXEC card of the IMSO or IMSl procedure. However" the user must stipulate a DMB pool large enough to accommodate all HISAM DMB's used for online processing and his largest HSAM DMB or the HSAM DMB used in data base dump for the largest HISAM data base.
PSB Size Calculation. The exact main storage occupancy for a PSB may 'be calculated by adding the size of the PSB prefix (PSBPFX), the size of a teleprocessing program communication block (TPCBSZ), and the size of each data base program communication block (DPCBSZ). The formula for the calculation is:
PSBSIZE=PSBPFX + (TPCBSZ*n) + DPCBSZ, ••• +DPCBSZn
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)
,
~e~:
PSBPFX = 44 bytes
TPCBSZ = 96 bytes if the PSB generation PSBGEN statement contains the keyword LANG = PL/I
= 40 bytes. i f keyword LANG=COBOL or ASSEM
OPCBSZ = 112+(132*OSGn)+(44*SSEGn) + (LEVs*LEVn)+MKFBs + (12*FLOn) where:
OSGn = number of data set groups defined; varies from 1 through 9
SSEGn = number of sensitive segment names defined: varies from 1 through 255
LEVs = 16 bytes plus the length of largest key field as defined by a FLDK statement in the associated data base
definition. rounded up to the next fullword
LEVn = number of levels in the data base hierarchy: varies from 1 through 15
MKFBs = length of maximum concatenated key as specified in the KEYLEN = keyword of the PCB statement
FLDn = number of FLD statements in the associated data base definition
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Note: If the OBOUMP command is to be used, the PSB pool must be large enough to contain a PSB that is twice the size of the largest possible data base PCB plus the PSBPFX size.DMB Size Calculation. The exact storage occupancy for a OMB may be calculated by adding the size of the DMB prefix to the size of the DCB's required for each data set group (DSG) that comprises the data base and the number of segment types times a constant. The formula for size calculation is:
DMBSIZE = [(IDCBSZ + ODCBSZ + DSGPFX) * DSGN] + DMBNSZ + (NSEGT * 4) which reduces to:
OMBSIZE = where:
IDCBSZ
=
ODCBSZ = DSGPFX = DMBNSZ = NSEGT = DSGN =
(488 * OSGN) + 8 + (NSEGT * 4)
252 bytes for an ISAM DCB 228 bytes for an OSAM DCB eight bytes
eight bytes for OMB name
number of segment types, where O<NSEGT< 256 number of data set groups in the data base Operating System/360 Requirements
Additional core storage is required in the IMS/360 Type 0 region for some Operating System/360 modules and control blocks. In addition, when MVT is used. core storage is required in the system queue space area.
MFT:
Task I/O Table (TIOT) = 28 + 16n + 4d n
=
number of DD cards d=
number of I/O devicesProgram Request Blocks (PRB) (two required) = 64 bytes supervisor Request Blocks (SVRB) (at least one
required)
=
96 bytesLoaded Program Request Blocks (LPRB) (38 required) = 1520 bytes Data Extent Blocks (DEB) - 160 bytes each
(one required per communication line group) (five DEB's required for log and message queues) (one DEB per ISAM data set in each data base) Data set Integrity (see MVT)
System Fetch Work Area OPEN/CLOSE/EOV Work Area ABEND Work Area
Input/Output Blocks (IOB)
(one IOB per communication line) (two IOB's per data set)
390 bytes 1200 bytes 1000 bytes 136 bytes
MVT: The MVT requirements are divided between the space required in System Queue Space and the IMS/360 Type 0 region.
System Queue Space:
TIOT
=
(28 + 16n + 4d) bytes n = number of DD cards d=
number of I/O devicesMain storage Control Blocks and Misc.
PRB's (two required) SVRB (one required)
LLE,XLr
&
CDE (40 required) DEB's - 160 bytes each(one per communication line group) (one per ISAM data set)
(two per OSAM data set)
(five for log and message queues) TCB's (three required)
Data Set Integrity Queue Blocks
500 bytes 64 bytes 96 bytes 1160 bytes
504 bytes
sum of nd (14 + L) where nd is number of data sets allocated and L is number of bytes in the data set name including concatenation characters
/'
)
)
Type 0 Region:
System Fetch Work Area OPEN/CLOSE/EOV Work Area ABEND Work Area
16 - 2740/1050 communication lines (16 terminals) 1 - 2260 line (four terminals) Basic Storage Requirement
2740 Station Control, Autopoll, Checking
"2260
1050 - Nonswitched with Autopoll
lMS/360 Control Blocks (step 36 system definition)
Total lMS/360 Requirements 155,708