| From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
|---|---|
| To: | Stephen Frost <sfrost(at)snowman(dot)net> |
| Cc: | Amit Kapila <amit(dot)kapila16(at)gmail(dot)com>, Robert Haas <robertmhaas(at)gmail(dot)com>, Jesper Pedersen <jesper(dot)pedersen(at)redhat(dot)com>, Jeff Janes <jeff(dot)janes(at)gmail(dot)com>, pgsql-hackers <pgsql-hackers(at)postgresql(dot)org> |
| Subject: | Re: Write Ahead Logging for Hash Indexes |
| Date: | 2017-03-15 14:43:24 |
| Message-ID: | 2328.1489589004@sss.pgh.pa.us |
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| Lists: | pgsql-hackers |
Stephen Frost <sfrost(at)snowman(dot)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
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