hole punching performance

[Bradley C. Kuszmaul]

Where can I read about extents and xfs?

On Sun, Jan 13, 2013 at 4:26 AM, Florian Weimer <fw at deneb.enyo.de> wrote:

> * Bradley C. Kuszmaul:
>
> > The question I have:  What will happen to the performance of other
> > threads doing read() and write() operations?  Will hole-punching slow
> > down the other read() and write() operations running in other threads?
>
> Assuming that hole-punching creates extents (not sure if it does, you
> can check with filefrag or other tools), you might experience a
> slowdown during open(), when the entire list of extents is read from
> disk.
>
> I once was a heavy Berkeley DB user and had files with dozens of
> gigabytes containing hundreds of thousands of extents, and open()
> times in the order of minutes were not unusual with a cold cache and
> other concurrent read activities from the same RAID device.  But these
> files grew over time—perhaps hole punching results in better locality
> of the extent data, so that reading it doesn't take so much time in
> your case.
>
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