User specifications for file attributes are mapped onto actual values by means of defaulting mechanisms; these supply any values not explicitly specified by the user and may even modify explicitly specified values, where necessary. The following defaulting mechanisms exist:
defaults for individual location-relevant attributes via storage classes and default storage classes (STORAGE-CLASS attribute)
default for the file format (FILE-PREFORMAT attribute)
default for the availability (AVAILABILITY attribute)
default for the performance-related attributes (PERFORMANCE attribute)
default for file type “work file” (WORK-FILE attribute)
default for the S0-MIGRATION attribute
default for the MIGRATE attribute
These mechanisms are explained below for the command interface (mostly CREATE-FILE and MODIFY- FILE-ATTRIBUTES). The comments apply analogously to the program interfaces (macros CATAL and FILE).
Assigning defaults for the individual location-relevant attributes via storage classes and default storage classes
Storage classes must be defined by systems support. The values defined in a storage class are used to determine the location-relevant file attributes WORK-FILE, PERFORMANCE, USAGE, DISK-WRITE, FILE-PREFORMAT and AVAILABILITY. The performance value may be reduced by the system, taking the user authorization DMS-TUNING-RESOURCES into account.
Default storage classes (user- and pubset-specific)
Systems support can define a specific default storage class for each user on each SM pubset. This causes the attribute settings of the user-specific storage class to be assumed for each initial storage space allocation on the pubset under that user ID unless any of the following specifications is made:
Explicit specification of a storage class
PERFORMANCE *)
STORAGE-CLASS=*NONE (*)
USAGE *)
WORK-FILE=*NO *)
DISK-WRITE *)
WORK-FILE=*YES
AVAILABILITY *)
Physical allocation
*) | If there is no authorization to perform physical allocation then the default storage classoverrides the specifications marked with *) (and not vice versa). |
The command SHOW-USER-ATTRIBUTES PUBSET=...,INFORMATION=*PUBSET-ATTRIBUTES indicates whether or not a user-specific default storage class exists.
The user can define a default storage class for each file generation group in an SM pubset (STOR-CLASS-DEFAULT operand of the CREATE-FILE-GROUP command). During initial storage space allocation for a file generation, the attribute settings of this storage class are used subject to the same conditions as for files. The default storage class of a file generation group can be specified explicitly, or the user-specific default storage class (STOR-CLASS-DEFAULT=*STD) of the SM pubset where the file generation group is created is assigned.
Assigning a storage class
A storage class can be assigned to a file (or file generation) either explicitly (by specifying STORAGE-CLASS=<composed-name>) or via the default (STORAGE-CLASS=*STD). A file or file generation cannot be assigned a storage class until it is allocated storage space. At that time the location-relevant attributes are assigned as well.
Until a file has been allocated storage space, the values of the location-relevant file attributes AVAILABILITY, WORK-FILE and FILE-PREFORMAT as well as the storage class assignment are undefined. This also applies if a file was allocated space and the entire space has been released (commands DELETE-FILE or MODIFY-FILE-ATTRI-
BUTES...,SPACE=*RELEASE(...)).
The following must be taken into account when cancelling a storage class assignment for a file (MODIFY-FILE-ATTRIBUTES...,STORAGE-CLASS=*NONE):
The name of the storage class is removed from the catalog entry. Only location-relevant attributes specified explicitly are modified. To ensure that contingents, if any, are not ignored, the PERFORMANCE and AVAILABILITY values for files with the (derived) attribute S0-MIGRATION=*FORBIDDEN may, however, be modified in accordance with the corresponding values of the volume set on which the file is residing.
Default file preformat
The commands CREATE-FILE and MODIFY-FILE-ATTRIBUTES, as well as the commands for creating and modifying storage classes permit the value *BY-PUBSET-DEFAULT, which is also the default value, to be specified for the PREFORMAT attribute. The effect of this default value differs, depending on whether the file was created via physical allocation or not:
A file created via physical allocation is assigned the format of the volume set on which it is created as preformat.
A file not created via physical allocation is assigned the default file format of the SM pubset as preformat. The preformat is taken into account for the selection of a suitable volume set.
In addition, the preformat has an influence on the final file format assigned when the file is opened for creation: If the user opens the file without specifying a format explicitly (ADD-FILE-LINK or FCB), the preformat is used as default.
See the sections on "Determining the preformat" and "Determining the file format" for more details about determining the file preformat and the final file format.
Default availability
*STD is the default availability value for files not created via physical allocation. For files created via physical allocation, the attribute value is determined on the basis of the user specifications as follows:
AVAILABILTY value of the volume set on which the file is created | User-specified file attribute AVAILABILITY | Resulting value of the file attribute AVAILABILITY |
|---|---|---|
HIGH | not explicitly specified | HIGH |
STD | not explicitly specified | STD |
If S0-MIGRATION=*FORBIDDEN is set (explicitly via the MODIFY-FILE-ATTRIBUTES command or implicitly via physical allocation) and the file occupies storage space on a volume set with the attribute AVAILABILITY=*HIGH, the same value AVAILABILITY=*HIGH is set for the file (even if the user explicitly specifies AVAILABILITY=*STD).
Defaults for static performance-related attributes
A distinction is made between static and dynamic values of performance attributes (see section "Sequence of OPEN processing"). Static values are stored in the catalog entry, dynamic values are either stored in the TFT or specified in the TU FCB. Explicit user specifications or values taken from the storage classes may be reduced by the system, taking the DMS-TUNING-RESOURCES entry for the file owner into account.
To ensure that contingent monitoring cannot be ignored when creating a file via physical allocation, the CREATE-FILE command may replace user-specified values or existing settings for the static PERFORMANCE attribute by higher values depending on the performance characteristic of the predefined volume set.
PERFORMANCE values of the volume set | User-specified file attribute PERFORMANCE | Resulting file attribute PERFORMANCE with physical allocation |
|---|---|---|
STD [,HIGH] [,VERY- | not explicitly specified | STD |
HIGH [,VERY-HIGH] | not explicitly specified | HIGH |
VERY-HIGH | not explicitly specified | VERY-HIGH |
The higher settings effected by CREATE-FILE may even exceed the file owner's DMS-TUNING-RESOURCES authorization.
The value for static file performance determined by the MODIFY-FILE-ATTRIBUTES command is dependent on the value of the S0-MIGRATION attribute after execution of the command:
If command execution results in S0-MIGRATION=*FORBIDDEN, the user-specified performance (in the event of explicit specification) or the static performance hitherto assigned to the file may be modified automatically. The rules for creating a file via physical allocation apply in this case as well. Again, the resulting static performance value may exceed the file owner's DMS-TUNING-RESOURCES authorization.
If command execution results in S0-MIGRATION=*ALLOWED, the performance explicitly specified by the user will be reduced to avoid exceeding the DMS-TUNING-RESOURCES. In the absence of any explicit performance specification, the current performance value is retained.
Default for file type “work file”
By default, files are created as permanent files (WORK-FILE=*NO). A work file can be created using the following mechanisms:
explicit specification of WORK-FILE=*YES
physical allocation (explicit specification of a disk that belongs to a work volume set by means of the VOLUME operand or explicit specification of a work volume set via the VOLUME-SET operand)
specification of a storage class for which WORK-FILE=*YES applies.
No file already occupying storage space can be redefined as a work file.
Default for the S0-MIGRATION attribute
The CREATE-FILE command sets the default value for this attribute. With physical allocation, this results in the allocation S0-MIGRATION=*FORBIDDEN, otherwise in S0-MIGRATION=*ALLOWED.
In the MODIFY-FILE-ATTRIBUTES command, the specification S0-MIGRATION=*UNCHANGED sets the default value for this attribute. For files already occupying storage space, this causes the current value to be retained even if the command simultaneously extends the file via physical allocation. For files which do not yet occupy any storage space and are assigned storage space using the MODIFY-FILE-ATTRIBUTES command, the S0-MIGRATE value is determined as for a newly created file.
Default for the MIGRATE attribute
The CREATE-FILE command sets the default value for this attribute. With physical allocation at volume or block level, this results in MIGRATE=FORBIDDEN. For files not created via physical allocation, a distinction is made between permanent and temporary files: for temporary files MIGRATE=INHIBITED is assigned, and for permanent files MIGRATE=ALLOWED.
In the MODIFY-FILE-ATTRIBUTES command, the specification MIGRATE=*UNCHANGED sets the default value for this attribute.
The effect is different for files already occupying storage space and those not yet occupying storage space:
For files already occupying storage space, the current value of MIGRATE is retained unless the file is simultaneously converted from a temporary to a permanent file.
Temporary files are automatically assigned MIGRATE =INHIBITED. Any extension of the file via physical allocation has no effect on the setting of the MIGRATE value.
For files not yet occupying any storage space and being assigned storage space via the MODIFY-FILE-ATTRIBUTES command, the MIGRATE value is determined as for a newly created file.