Using Xapian through a pipe

To avoid linking with Xapian you can use a port:

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xapian_server:open(Path, [port]).

C-port allows to use Erlang VM and Xapian in different memory spaces. If a port crashes, Erlang VM will be still alive.

But I think, it does not help to avoid GPL restrictions: the whole program will be a derivative work.

GPL is a sly license. :)