These are the packages that would be merged, in order:

Calculating dependencies ... done!
Dependency resolution took 2.00 s (backtrack: 0/20).

[ebuild  N     ] sys-libs/db-6.0.35-r5:6.0::gentoo  USE="-cxx -doc -examples -tcl -test" 35677 KiB
[ebuild     U  ] dev-lang/perl-5.42.2:0/5.42::gentoo [5.42.0-r1:0/5.42::gentoo] USE="berkdb* gdbm -doc -minimal" PERL_FEATURES="ithreads (-debug) -quadmath" 14278 KiB
[ebuild  N     ] virtual/perl-DB_File-1.859.0-r1::gentoo  0 KiB

Total: 3 packages (1 upgrade, 2 new), Size of downloads: 49954 KiB

The following USE changes are necessary to proceed:
 (see "package.use" in the portage(5) man page for more details)
# required by virtual/perl-DB_File-1.859.0-r1::gentoo
# required by =virtual/perl-DB_File-1.859.0-r1 (argument)
=dev-lang/perl-5.42.2 berkdb

emerge: there are no ebuilds built with USE flags to satisfy "=dev-lang/perl-5.42*[berkdb]".
!!! One of the following packages is required to complete your request:
- dev-lang/perl-5.42.0-r1::gentoo (Change USE: +berkdb)
(dependency required by "virtual/perl-DB_File-1.859.0-r1::gentoo" [ebuild])
(dependency required by "=virtual/perl-DB_File-1.859.0-r1" [argument])