ACCESS M::::THOD Size 1 Size 2 - The information contained in this

GSAM Input/Output invalid

HISAM Primary(KSDS) Overflow(ESDS)

SHISAM Primary(KSDS) N/A8

HDAM Data(ESDS) invalid'

HIDAM Data(ESDS) invalid 10

INDEX Primary(KSDS) Overflow(ESDS)

DED8 Data(ESDS)10 invalid

Figure 33. Relation of SIZE subparameters to Access Methods

Although there ~s a choice of whether to use the BLOCK~

RECORD

SIZE

parameters for the various data base organizations, there is a recommended parameter combination fQr each of the available organizations.

For a GSAM data base, the

BLOCK

and

RECORD

parameters should be used in conjunction. The control interval size that will be used for the GSAM data base is the product of the specifications 'for the blocking factor and the record length plus the system overhead rounded up to the next larger valid control interval size. The valid control interval sizes are described in section "Control Interval and Control Area Definition and Concept" on page 4. The system overhead included in the calculation of the control inter-val size is shown in Figure 34 on page 57.

for HISAM~ SHISAM and INDEX data bases, it is suggested that the

SIZE

parameter be used instead of

BLOCK

and

RECORD.

DEDB data bases must be defined with the

SIZE

parameter. When

SIZE

is used, the value specified is the actual control interval size that is desired. This value must be equal to one of the valid control interval sizes. If i t is not~ then the value is

-~rounded upwards to the next valid size and DBD generation will issue a warning message. Although there is no overhead added to the value

speci-8

A SHISAM data base has no Overflow component and it is therefore invalid to specify the

'size 2'

subparameter for SHISAM'

The

SIZE

parameter applies only to the data component of the HD data base organizations and the

'size 2'

subparameter is meaningless when specified for either of the HD organizations.

The

SIZE

parameter is reguired for a DEDB data base.

f ied for the

SIZE

parameter, the user must be aware of the overhead requirements in order to be able to select the appropriate control inter-val size. The overhead requirements for these data base organizations is shown in Figure 34.

When either HDAM or HIDAM data base are being defined the second form of the

BLOCK

parameter is to be used. The size specified is for the data (ESDS) component of the data base. In this case, the value specified for the

BLOCK

parameter is the amount of space required for the segments that are to be placed in each block. DBD generation will add to this value the space needed for root anchor points, a free space anchor point and the VSAM control information. The result is then rounded up to the next valid control interval size.

The amount of space required for the anchor points and VSAM control infor-mation is shown in Figure 34.

Access Character- VSAM DL/I Total

Method isties Overhead Overhead Ovrhd

GSAM Block = 1 3(RDF) + 4(CIDF) 0 7

GSAM ^/ fixed rcd.

SHISAM Bloclc > 1 2*3CRDF) + 4(CIDF) 0 10 GSAM variable rcd. 3*block.factorCRDF)

Block > 1 + 4(CIDF) 0 >=10

HISAM 3CRDF) + 4CCIDF) 5 12

INDEX unique lcey 11 3(RDF) + 4(CIDF) 0 7

INDEX nonunique key 3(RDF) + 4(CIDF) 4 1 1

HDAM 3(RDF) + 4(CIDF) 4 for FSAP

4 per RAp12 >=15

HIDAM 3(RDF) + 4(CIDF) 4 for FSAp13

4 for 1 RAP 11/15

Figure 34. VSAM and DL/I overhead to be used for CI size calculation

11 This case also applies to the Primary Index of an HIDAM data base which, by definition must have unique keys.

12 The number of Root Anchor Points (RAPs) in each control interval is determined by the value specified as the second subparameter of the

RMNAM~ macro as explained in "RMNAME" on page 51.

13 A Free Space Anchor Point (FSAP) will only be used in an HIDAM data base if no pointers other than Hierarchical Forward .and Physical Twin Pointers are specified for the root segment.

4.1.2.4 RECFM for GSAM/VSAM

This parameter applies only to GSAM data bases and may not be specified for any other data base organization.

The values of this parameter which may be used with a VSAM-based GSAM data base are:

F indicates that the records are fixed length.

FB

indicates that the records are fixed length and blocked.

Y indicates that the records are of variable length.

VB

indicates that the records are of variable length and are blocked.

When the GSAM data base is specified as having variable length records~ it is assumed that the first two bytes of the record contain the record length. This record length must be supplied by the user when creating new records and is supplied by DL/I when the records are retrieved.

For the fixed length record formats, the record length need not be speci-fied. The use of blocked formats is recommended for VSAM unless the size of the GSAM data base records is such that only one record will fit into a control interval.

4.1.2.5 FRSPC

The

FRSPC

parameter is only applicable to HDAM and HIDAM data bases. When this parameter is used for a VSAM data base, it specifies the amount of free space to be allowed in the ESDS component of the data base at initial load time. The ESDS component of an HIDAM data base is that portion con-taining the actual data segments. For an HDAM data base, the parameter applies only to that portion of the ESDS which has been defined to be the root addressable area using the

RMNAME

parameter as explained in "RMNAME"

on page 51 .

This parameter has the following format:

FRSPC=(Free Block Frequency Factor,Free Space percentage Factor)

The meaning and use of the the subparameters has been discussed earlier in

"DL/I - ESDS Free Space" o·n page 24.

4.1.2.6 Fast Path Parameters

for fAST PATH data sets which

must

VSAM

data sets the parameters UOW (Unit-of-Work) and ROOT must be specified. A detailed description of their function and specification is included in chapter "fast Path Feature" on page 103. The format of the UOW parameter is as follows:

UOW=(number 1, overflow 1)

The format of the ROOT parameter is as follows:

ROOT=(number 1, overflow 1)

4.1.3 other

DBO

Parameters That Affect VSAM

Because the other macros in DBD generation do not affect VSAM in as direct.

a manner as do the

DBD

and

DATASET macros,

the remaining parameters for which there are VSAM considerations are treated as a group rather than macro by macro.

4.1.3.1 Pointer Specifications

The use of pointers in the data base organizations has a bearing on VSAM in that it will affect the size of segment prefiKes. These segment pre-fixes must be included in the total size of the segments when making the determination of control interval sizes.

Dans le document The information contained in this (Page 64-67)