Asynchronous CF Lock Duplexing with SAP Performance Report from IBM zSystems
Document Author: Additional Author(s):
Seewah Chan, Paul Lekkas
DB2 for z/OS and OS/390; IBM System z; Parallel Sysplex; SAP
Abstract: Asynchronous CF Lock Duplexing is a new enhancement to IBM’s parallel sysplex technology that was made generally available in October 2016. It is an alternative to the synchronous system managed duplexing of coupling facility (CF) lock structures that has been available for many years. The new Asynchronous CF Lock Duplexing feature was designed to be a viable alternative to synchronous system managed duplexing. The goal was to provide the benefits of lock duplexing without the high performance penalty. It eliminates the synchronous mirroring between the CFs to keep the primary and secondary structures in sync.
The IBM SAP on z Systems Performance Team, located in Poughkeepsie, NY, conducted a number of tests on an IBM z13 to evaluate the performance effects of using the Asynchronous CF Lock Duplexing protocol. We used the SAP Banking Services (SBS) Day Posting workload. We ran tests with simplex CF lock structures (i.e. no lock duplexing), synchronous system managed CF lock structures, and asynchronous duplexed CF lock structures with various distances between our CFs. We started our testing using virtual CF links (i.e. no distance between the CFs) to verify our configurations and the various locking protocols. We then moved on to testing with 150 meter CF links (short distance) and then with 10 Km CF links (long distance). We also tested a recovery scenario while running the SAP Day Posting workload using asynchronous duplexed CF lock structures where we failed the CF with the primary lock structure. We wanted to confirm that the new protocol was essentially keeping the secondary structure in sync with the primary.