/usr/lib/x86_64-linux-gnu/libdb_cxx.so is in libdb6.0++-dev 6.0.19-3ubuntu1.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/lib/x86_64-linux-gnu/libdb_cxx-6.0.so
/usr/lib/x86_64-linux-gnu/libdb_cxx-6.0.so