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Re: [Bug-tar] Detection of sparse files is broken on btrfs
From: |
Tim Kientzle |
Subject: |
Re: [Bug-tar] Detection of sparse files is broken on btrfs |
Date: |
Wed, 17 Jan 2018 20:49:53 -0800 |
> On Jan 17, 2018, at 1:09 PM, Andreas Dilger <address@hidden> wrote:
>
>> So is there some other way to quickly identify sparse files so we can avoid
>> the SEEK_HOLE scan for non-sparse files?
>
> Given that calling SEEK_HOLE is also going to have some cost, my suggestion
> would be to ignore st_blocks completely for small files (size < 64KB) and
> just read the file in this case, since the overhead of reading will probably
> be about the same as checking if any blocks are allocated. If no blocks are
> allocated, then the read will not do any disk IO, and if there are blocks
> allocated they would have needed to be read from disk anyway and SEEK_HOLE
> would be pure overhead.
If I understand, you’re basically suggesting not bothering
with the sparse-file storage for small files (size < 64k).
This makes a lot of sense to me: sparse file storage
is most important for applications (e.g., databases) that
use large files as randomly-accessible swap space and need
to preserve sparseness (to not blow out disk) and/or
non-sparseness (so that overwrites don’t require
allocations).
So skipping the SEEK_HOLE check for common
small files seems like a good optimization.
Cheers,
Tim
- Re: [Bug-tar] Detection of sparse files is broken on btrfs, (continued)
- Re: [Bug-tar] Detection of sparse files is broken on btrfs, Paul Eggert, 2018/01/08
- Re: [Bug-tar] Detection of sparse files is broken on btrfs, Joerg Schilling, 2018/01/08
- Re: [Bug-tar] Detection of sparse files is broken on btrfs, Paul Eggert, 2018/01/08
- Re: [Bug-tar] Detection of sparse files is broken on btrfs, Joerg Schilling, 2018/01/08
- Re: [Bug-tar] Detection of sparse files is broken on btrfs, Paul Eggert, 2018/01/08
- Re: [Bug-tar] Detection of sparse files is broken on btrfs, Joerg Schilling, 2018/01/09
- Re: [Bug-tar] Detection of sparse files is broken on btrfs, Tim Kientzle, 2018/01/09
- Re: [Bug-tar] Detection of sparse files is broken on btrfs, Paul Eggert, 2018/01/09
- Re: [Bug-tar] Detection of sparse files is broken on btrfs, Joerg Schilling, 2018/01/10
- Re: [Bug-tar] Detection of sparse files is broken on btrfs, Andreas Dilger, 2018/01/17
- Re: [Bug-tar] Detection of sparse files is broken on btrfs,
Tim Kientzle <=
- Re: [Bug-tar] Detection of sparse files is broken on btrfs, Andreas Dilger, 2018/01/18
- Re: [Bug-tar] Detection of sparse files is broken on btrfs, Joerg Schilling, 2018/01/18
- Re: [Bug-tar] Detection of sparse files is broken on btrfs, Paul Eggert, 2018/01/09
- Re: [Bug-tar] Detection of sparse files is broken on btrfs, Joerg Schilling, 2018/01/10
- Re: [Bug-tar] Detection of sparse files is broken on btrfs, Paul Eggert, 2018/01/17
- Re: [Bug-tar] Detection of sparse files is broken on btrfs, Ralph Corderoy, 2018/01/17
- Re: [Bug-tar] Detection of sparse files is broken on btrfs, Andreas Dilger, 2018/01/17
- Re: [Bug-tar] Detection of sparse files is broken on btrfs, Joerg Schilling, 2018/01/18
- Re: [Bug-tar] Detection of sparse files is broken on btrfs, Paul Eggert, 2018/01/18
- Re: [Bug-tar] Detection of sparse files is broken on btrfs, Joerg Schilling, 2018/01/19