Hi,
Duplexed requests are more costly than simplex requests. Generally
applications "feel" this most significantly via longer service times.
In terms of comparing the actual CPU cost to the two CF's for
processing a duplexed requests, the correct answer is "it depends". It
depends on what operations the application is driving to the structure and
the z/OS implementation. Some examples of the sorts of things that come
into play here:
- For many operations, the same command will be sent to both facilities.
Here I'd expect equal CPU cost.
- For some operations, the commands sent to the two structures are
different. For example, if the application is doing a "read and delete" of
an object, both CF's need to delete the object but only one of them needs
to do the work to send back the data.
- For some operations, z/OS issues a simplex request to one of the
structure instances to determine what objects are to be processed, and then
drives duplex commands to both CFs to process those objects. Again, those
duplexed commands will generally be identical, but I would not be surprised
if there are cases where they are different.
In current practice, it is reasonable to assume that the CF CPU cost
of for the secondary structure instance is no worse than the cost for the
primary instance.
Mark A. Brooks
z/OS Sysplex design and development
845-435-5149 T/L 8-295-5149
Poughkeepsie, NY
mabr...@us.ibm.com
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