OPEN modes for shared-update processing

The first user who opens an ISAM file may specify any possible combination of the values valid for OPEN and SHARUPD. The following table shows which combinations of OPEN and SHARUPD are permitted for user B if user A has already opened the file. If the file has already been opened by more than one user, the OPEN/SHARUPD combination specified by user B is compared with all other OPEN/SHARUPD combinations. Uer B may open the file only if the results of this comparison permit it.

USER B

SHARUPD=

*YES

*NO

OPEN mode

I N P U T

I N O U T

E X T E N D

O U T I N

O U T P U T

I N P U T

I N O U T

E X T E N D

O U T I N

O U T P U T

U S E R A

*YES

INPUT INOUT EXTEND OUTIN OUTPUT

X X X X X

X X X X X

X X

X

X X

*NO

INPUT INOUT EXTEND OUTIN OUTPUT

X

X

Table 57: ISAM: Permissible SHARUPD/OPEN combinations

X indicates that this OPEN mode is permitted for user B.

Note on the NK-ISAM access method

When files are accessed in SHARUPD=YES mode, it is possible that processing will result in a file < 32 GB growing to become a file >= 32 GB.

Here it is necessary to distinguish between two cases:

• Callers who are prepared for this situation (with the specification
  LARGE_FILE=*ALLOWED in the FCB macro or EXCEED-32GB=*ALLOWED in the ADD-FILE-LINK command)

• Unprepared callers (specification LARGE_FILE=*FORBIDDEN in the FCB macro or EXCEED-32GB=*FORBIDDEN in the ADD-FILE-LINK command).

On each SVC entry, the size of the NK-ISAM file in question is checked on the basis of the extent list present in the File Entry Table. If this check indicates that the file size is greater than 32 GB and if the caller has set the attribute LARGE_FILE=*FORBIDDEN in the FCB then processing is canceled. In this case, NK-ISAM issues the return code.

X'00000A23' FILE SIZE GREATER 32 GIGABYTES IS NOT ALLOWED.

(or the corresponding DMS message: DMS0A23)

The K-ISAM access method (BLKCTRL=PAMKEY ) is not affected by this problem.