Re: [HACKERS] Write Ahead Logging for Hash Indexes

Stephen Frost <sfrost@snowman.net> writes:
> I do see that mdwrite() should handle an out-of-disk-space case, though
> that just makes me wonder what's different here compared to normal
> relations that we don't have an issue with a sparse WAL'd hash index but
> we can't handle it if a normal relation is sparse.

*Any* write has to be prepared to handle errors.  There's always a risk of
EIO, and on a COW filesystem you might well get ENOSPC even when you think
you're overwriting previously-allocated storage.  All that we are doing by
pre-allocating storage is reducing the risks a bit, not guaranteeing that
no error will happen.
        regards, tom lane