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/