Multi-user mode

A PAM file can be created or processed in parallel using the following access methods:

• FASTPAM

• UPAM (see chapter "UPAM - User Primary Access Method" (UPAM - User Primary Access Method))

• DIV (see chapter "DIV - Data In Virtual" (DIV - Data In Virtual))

Permissible combinations of opening a file in parallel

			USER B
	SHARUPD=		*YES			*NO			*WEAK
		OPEN mode	I N P U T	I N O U T	O U T I N	I N P U T	I N O U T	O U T I N	I N P U T	I N O U T	O U T I N
U S E R A	*YES	INPUT INOUT OUTIN	X O O	O O O		X			X X X
	*NO	INPUT INOUT OUTIN	X			X			X X X
	*WEAK	INPUT INOUT OUTIN	X	X		X	X		X X X	X

Table 47: FASTPAM: Permissible SHARUPD/OPEN combinations

X:	OPEN permitted
O:	OPEN permitted only if the same block-oriented access method is used by all (either UPAM/FASTPAM or DIV) and the same value is used by all for the LOCKENV operand (either LOCKENV=*HOST or LOCKENV=*XCS) and all are running on the same host or, with LOCKENV=*XCS, in an XCS network

Notes

• A file can be opened with SHARUPD=*WEAK for concurrent reading and writing. (SHARUPD=*WEAK is possible with UPAM and DIV only.)

  Exception:
  When users read with DIV-SHARUPD=*WEAK after specifying LOCVIEW=*MAP in the OPEN call, parallel opening for writing with UPAM/FASTPAM is not permissible.

  The conditions applying to reading with UPAM/FASTPAM-SHARUPD=*WEAK also apply to reading with DIV-SHARUPD=*WEAK after specifying OPEN LOCVIEW= *NONE.

• Users opening with DIV-SHARUPD=*YES are not compatible with users opening with UPAM/FASTPAM-SHARUPD=*YES.

• Read operations are always compatible irrespective of the access method, the values specified for SHARUPD and LOCKENV and the host.

• Illegal combinations result in an OPEN error.

• 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).

  The size of the file in question is checked after every allocator call. If this check indicates that the file size is >= 32 GB and the LARGE_FILE=*FORBIDDEN attribute is set in the associated FCB, then processing is canceled and a corresponding return code is output in the local parameter list FPAMSRV(I) or a DMS message is issued.

The following points apply to the FASTPAM access method:

• A file can be concurrently processed with FASTPAM by multiple tasks (multiple OPENs with SHARUPD=*YES and MODE=*OUTIN/*INOUT).

  When a file is accessed in shared-update mode, appropriate synchronization routines must be supplied by the user if no such routines are built into the software product being used. In contrast to UPAM, FASTPAM does not provide any locking mechanism for this purpose.

• Opening with FASTPAM and UPAM

  A file can be opened in parallel by multiple tasks with FASTPAM as well as UPAM. Processing of the file is controlled by the operands MODE and SHARUPD (see below) of the OPEN function. Although FASTPAM does not support SHARUPD=*WEAK, it otherwise behaves exactly like UPAM: both for exclusive FASTPAM open operations and also when UPAM and FASTPAM are mixed.

  When a file is concurrently accessed with UPAM and FASTPAM, the UPAM user must also synchronize operations with the FASTPAM user, since UPAM page locks are only effective when used by both sides, and since FASTPAM has no page-locking mechanism.

• Opening with FASTPAM and DIV

  FASTPAM interacts with DIV exactly like UPAM. Parallel processing is permitted only if the file is opened with INPUT by all users.

• Files on shared pubsets (SPVS) are supported by FASTPAM: FASTPAM users can access an SPVS from different systems and read from it concurrently and can also read in parallel with UPAM and DIV users.

• Cross-system file access (RFA) is not supported.