Confusing error message with too-large file in pg_basebackup

Version: 9.4.5
Summary: confusing error message for too-large file failure in pg_basebackup

Details:

1. PostgreSQL previously core dumped on this system and left behind a
9gb core file, which was never deleted.

2. Attempted to pg_basebackup the server.

3. Got this error message:

pg_basebackup: could not get transaction log end position from server:
ERROR:  archive member "core" too large for tar format

This was very confusing to the user, because they weren't requesting tar
format, and even setting -Fp got the same error message.  I can only
hypothesize that tar is used somewhere under the hood.

pg_basebackup doesn't need to work under these circumstances, but maybe
we could give a less baffling error message?

--
Josh Berkus
PostgreSQL Experts Inc.
http://pgexperts.com