Sage advice. Thanks.

Trust me, I'm not ignoring anything. I've already determined that DBI/mysql can connect, that the XS-modules are being loaded... from the correct locations (i.e. the site's local CPAN). This much I now know. The CGI-environment, only, throws the _login mesage. I have examined INC, and ENV, (what's %::?) very closely throughout.

The crux of the question is:   what in the heck is different about this environment vs. the command line?” I can see that I have lots of XS-modules that are working just fine.

As I read perldoc DBI::DBD, I see that “The variables $DBD::Driver::{dr|db|st}::imp_data_size are not defined here, but in the XS code, because they declare the size of certain C structures.“, this is obviously a very-direct clue when considered in light of the messages that “imp_data_size was unexpectedly expanded.” I see that DBI.so and mysql.so both contain this symbol, viz:

grep -rilw imp_data_size . | grep \.so | xargs grep imp_data_size

BTW, there is method to my bulldog-madness. I'm “chatting” on this thread partly because I well know that there are interested-parties. These are not written to be “rants.” Anyone who (follows|has followed) in this rocky path will (see|have seen) these same rocks. When this thread finally reaches its successful conclusion, I hope it will be useful both in its final-post and in the posts leading up to it. That's my intention, anyway.