Sysplex shared data coherency method

TLDR: In this article, a method for controlling coherence of data elements sharable among a plurality of independently-operating central processing complexes (CPCs) in a multi-system complex (called a parallel sysplex) which contains sysplex DASDds (direct access storage devices) and a high-speed SES (shared electronic storage) facility is presented.

Abstract: A method for controlling coherence of data elements sharable among a plurality of independently-operating CPCs (central processing complexes) in a multi-system complex (called a parallel sysplex) which contains sysplex DASDds (direct access storage devices) and a high-speed SES (shared electronic storage) facility. Sysplex shared data elements are stored in the sysplex DASD under a unique sysplex data element name, which is used for sysplex coherence control. Any CPC may copy any sysplex data element into a local cache buffers (LCB) in the CPC's main storage, where it has an associated sysplex validity bit. The copying CPC executes a sysplex coherence registration command which requests a SES processor to verify that the data element name already exists in the SES cache, and to store the name of the data element in a SES cache entry if found in the SES cache. Importantly, the registration command communicates to SES the CPC location of the validity bit for the LCB containing that data element copy. Each time another copy of the data element is stored in any CPC LCB, a registration command is executed to store the location of that copy's CPC validity bit into a local cache register (LCR) associated with its data element name. In this manner, each LCR accumulates all CPC locations for all LCB validity bits for all valid copies of the associated data element in the sysplex -- for maintaining data coherency throughout the sysplex.