Performance implications of duplexing

The process of establishing duplexing can be somewhat disruptive because access to the group buffer pool structure is quiesced while the secondary structure is allocated. Also, changed pages are copied from the primary structure to the secondary structure (or cast out to disk).

Transactions that need access to the group buffer pool structure during this process are suspended until the process is complete. Because of this disruption, you need to establish duplexing at a time of low activity on the system. How long the process takes depends on how many pages are copied to the secondary group buffer pool structure.

In general, more processor and elapsed time is needed to do duplexed group buffer pool structure writes and castout processing than to do simplexed group buffer pool structure writes and castout processing. Workloads that are more update-intensive will probably experience a slight increase in host CPU usage when duplexing is activated. In most cases, the majority of the CPU increase occurs in the Db2 address space. Duplexing can cause a slight increase in the transaction elapsed time. Read performance is unaffected by duplexing.

The statistics and accounting trace classes contain information about structure duplexing.