George Dranes wrote:
I'm assuming the Server Pac install (z/os 1.7) used copymod to populate the linklib originally. There has been updates and deletes from maintenance being applied. I did compress the library before my copymod test. Copymod must be cleaning up some things in the process. As I said earlier, we usually use copy rather than copymod unless circumstances require copymod (blksize changes, device changes etc.).
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ServerPac has been using COPYMOD for some time, and was certainly using it prior to z/OS R7.
I believe what you are seeing is the effect of new and changed text blocks created by the Binder and by COPY being collapsed into a minimum number of text blocks by COPYMOD.
I think it very likely that COPY processing for compress only rearranges the text blocks you already have. The library was loaded originally with COPYMOD but then some members were modified, their original order was changed, and the result was an increase in unused space on some tracks. (I'd expect all those before the first altered member to be unaffected, and for things to "line back up" at some point after the last altered member if the data set has enough subsequent members.)
COPYMOD will realign all the text blocks with respect to track boundaries while minimizing their number for the data set's block size (you *are* using 32760, right?), and decrease the unused space in the data set. (You can only see this if you have a track mapping tool of some sort or if you dump the tracks and look.) There is gory detail in a post I made some time ago, which you can find in the archives.
The decrease in unused space will afford some improvement in Program Fetch performance for uncached modules, and when the system is near or at 100% busy the reduction in the percentage of time a PCI is missed can afford some savings in cycles, too.
Maybe Mark and I can talk about whether COPYMOD is worth it in San Diego...
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