Robert, * Robert Haas (robertmh...@gmail.com) wrote: > On Wed, Mar 15, 2017 at 10:34 AM, Tom Lane <t...@sss.pgh.pa.us> wrote: > > FWIW, I'm not certain that Stephen is correct to claim that we have > > some concrete problem with sparse files. We certainly don't *depend* > > on sparse storage anyplace else, nor write data in a way that would be > > likely to trigger it; but I'm not aware that we need to work hard to > > avoid it. > > That theory seems inconsistent with how mdextend() works. My > understanding is that we zero-fill the new blocks before populating > them with actual data precisely to avoid running out of disk space due > to deferred allocation at the OS level. If we don't care about > failures due to deferred allocation at the OS level, we can rip that > logic out and improve the performance of relation extension > considerably. If we do care about failures due to deferred > allocation, then leaving holes in the file is a bad idea.
That is a fantastic point. Thanks! Stephen
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