Short writes

We are currently debugging a problem with error messages like this:

ERROR:  53100: could not write block 2427137 of relation 
1663/706306048/706314280: No space left on device

The device has plenty of space left.  The problem appears to be this 
curious code in src/backend/storage/file/fd.c:
/* if write didn't set errno, assume problem is no disk space */if (returnCode != amount && errno == 0)    errno =
ENOSPC;

What is the rationale for making this assumption?

We haven't yet figured out why the above error happens, but I suggest 
that we at least make a more accurate error message.

-- 
Peter Eisentraut
http://developer.postgresql.org/~petere/