Access path describes the order
in which records are to be read.
Access paths can be kept on the
system permanently (such as physical or logical file) or temporarily.
OPNQRYF command may create a
temporary access path for use one time, and then discard the access path.
Types of Access Path
Arrival sequence access path
Keyed sequence access path
sequence access path
ü Sequentially, where each record is taken from the next sequential
physical position in the file.
ü Directly by relative records number, where the record number is
identified by its position from the start of the file.
Keyed sequence access path
It is based on the contents of
the key fields as defined in DDS. This type of access path is updated in the
contents of a key field is changed.
There are three ways of bounding the access path:
Access path maintenance
(MAINT) parameter of a physical file
Change Physical File (CHGPF)
Type choices, press Enter.
Physical file . . . . . . . . . Name
Library . . . . . . . . . . . *LIBL Name, *LIBL, *CURLIB
System . . . . . . . . . . . . . *LCL *LCL, *RMT, *FILETYPE
Source file . . . . . . . . . . *NONE Name, *NONE
Library . . . . . . . . . . . Name, *LIBL, *CURLIB
Expiration date for member . . . *SAME Date, *SAME, *NONE
Maximum members . . . . . . . . *SAME Number, *SAME, *NOMAX
Access path size . . . . . . . . *SAME *SAME, *MAX4GB, *MAX1TB
Access path maintenance . . . . *SAME *SAME, *IMMED, *REBLD, *DLY
Access path recovery . . . . . . *SAME *SAME, *NO, *AFTIPL, *IPL
*** The MAINT parameter specifies how access
paths are maintained for closed files.
While a file is open, the system maintains the access paths as
changes are made to the data (this data may be key field data of other file) in
But the same data can have access path in multiple file. Some files
may be open at that time and some file may be closed at that time. For open
file, the access path for will change at the time related data is modified. But
for closed file how the access path will change is being decided by this MAINT
e.g. The account no. field may be used by many a files as a part of
composite key field. In such a case if a file is updating this account no.
field or adding one more account no., in
such a case what should be the effect of this change if the other file using
this filed is not open at that time the change is made.
The three ways of maintaining access paths of closed files are:
*IMMED: Immediate maintenance of an access path
means that the access path is maintained as changes are made to its associated
data, regardless if the file is open.
*REBLD: Rebuild maintenance of an access path
means that the access path is only maintained while the file is open, not when
the file is closed; the access path is rebuilt when the file is opened the next
time. When a file with rebuild maintenance is closed, the system stops
maintaining the access path. When the file is opened again, the access path is
*DLY: Delayed maintenance of an access path
means that any maintenance for the access path is done after the file member is
opened the next time and while it remains open. However, the access path is not
rebuilt as it is with rebuild maintenance. Updates to the access path are
collected from the time the member is closed until it is opened again. When it
is opened, only the collected changes are merged into the access path.
*Note: If you
do not specify the type of maintenance for a file, the default is immediate maintenance.