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PDSE DATA SET SHARING Basics

Question & Answer


Question

What are the two supported PDSE SHARING modes and what constitutes improper PDSE sharing?

Answer

PDSE supports two modes of PDSE data set sharing, NORMAL and EXTENDED.


PDSESHARING NORMAL
  • Default PDSESHARING mode, specified by the PDSESHARING(NORMAL) IGDSMSxx parameter.
  • Provides the ability to share PDSE data sets on the data set level.
  • PDSESHARING(NORMAL) and PDSE_RESTARTABLE_AS(YES) are mutually exclusive parameters.
  • All sharing LPARs must be members of a single GRSPLEX (GRS RING).
  • allows multiple readers or a single writer
  • GRS enqueues are used to insure PDSE data set integrity.

The PDSESHARING NORMAL protocol provides a limited form of inter-system sharing. Many systems can concurrently access a PDSE that is OPEN for INPUT, or one system can access a PDSE that is OPEN for OUTPUT.

When a system accesses a PDSE that is OPEN for OUTPUT, that PDSE cannot be accessed for INPUT by any other system. Conversely, if any system accesses a PDSE that is OPEN for INPUT, that PDSE cannot be accessed for OUTPUT by any other system.

Updates in a PDSESHARING NORMAL environment require exclusive access and any updated attempt fails with an IEC143I 213-70 if the PDSE is opened for any level of access on another system in the GRSPLEX.



PDSESHARING EXTENDED
  • Recommended form of PDSESHARING
  • Implemented via the IGDSMSxx PDSESHARING(EXTENDED) parameter.
  • Facilitates the sharing of PDSE data sets at the member level.
  • All sharing LPARS must be members of the same SYSPLEX (XCFPLEX).
  • XCF signaling and GRS enqueues are used to insure and protect data set integrity. A coupling facility is not necessary as XCF communications can be across CTCs.
  • When processing under this environment any PDSE data set can be opened by multiple readers (OPEN for INPUT) and multiple writers (OPEN for OUTPUT).
The PDSESHARING EXTENDED protocol enhances the ability to share PDSE data set. Under EXTENDED sharing PDSEs can be shared by multiple systems for the reading of old members and the creation of new members.

EXTENDED sharing does not support member updates (OPEN for UPDATE) while the PDSE is shared. Update-in-place of existing members requires the PDSE to be accessed by only one system. If the PDSE is OPEN by some system other than the system doing the Update-in-place, the update-in-place fails.



Improper PDSESHARING

Improper PDSE sharing is defined as attempting to share PDSE data sets between systems that are not within a single GRSPLEX (NORMAL sharing) or among systems that are not within a single XCFPLEX (EXTENDED sharing).

Improper PDSE sharing can result in the corruption of the PDSE data set directory or PDSE member data.
                                                  
The directory of a PDSE data set is cached into the SMSPDSE or SMSPDSE1 address space when the data set is opened. This cached directory structure is maintained until the PDSE data set is closed. In a PDSESHARING EXTENDED environment notification (via IGWNOTIF macro) is communicated to all sharing systems when a PDSE is updated. This notification is sent via XCF and receipt of this notification causes the sharing systems to invalidate cached directory records and to reread the directory of the changed PDSE data set from DASD.

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Document Information

Modified date:
03 September 2021

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isg3T1027532

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