zfs discuss - May 2006 - Sparse file support in Java?

Does anyone know if there is support in Java for creating holes in a
sparse file (like one can do via fcntl(F_FREESP) in C)?  Would like to
avoid writing JNI code if there is already support for this somewhere in
the JDK.

	Chuck

The reason this is pertinent to ZFS is because you can do things with a
ZFS file that you can''t with other file systems.  In particular, with
ZFS you can use fcntl to free space from the file.  For example, a zfs
file can be used quite nicely to implement a circular queue.  Instead of
having to worry about wrap conditions, one can simply keep writing to
the end and punching increasingly larger holes starting at the
beginning.  This assumes, of course, that 2**64 is large enough to never
worry about a real wrap.  Just seeking and writing does not give you the
ability to change the size of an existing hole.

	Chuck  

-----Original Message-----
From: Bart Smaalders [mailto:Bart.Smaalders at Sun.COM] 
Sent: Monday, May 15, 2006 10:13 AM
To: Gehr, Chuck R
Subject: Re: [zfs-discuss] Sparse file support in Java?

Gehr, Chuck R wrote:
> Does anyone know if there is support in Java for creating holes in a 
> sparse file (like one can do via fcntl(F_FREESP) in C)?  Would like to
> avoid writing JNI code if there is already support for this somewhere 
> in the JDK.
> 
> 	Chuck

Not sure why this is on the zfs list....

just seek to where you wish to write; block-sized & aligned areas will
be "holey".

- Bart


-- 
Bart Smaalders			Solaris Kernel Performance
barts at cyber.eng.sun.com		http://blogs.sun.com/barts