rsync - May 2002 - Does the rsync/xdelta algorithm *need* to write a new file?

Hello,

lately I've been playing with the idea of doing in-place updates 
of systems using either rsync or xdelta. However, both rsync
and xdelta seem to be dead set on writing a new file first, and
then atomically exchanging it with the old file.

Now, as I want to apply a binary delta to a full filesystem, bigger 
than the available temporary space, this really makes rsync and
xdelta extremely tough to use (I could work around it, only updating 
blocks of half the size of the temporary space at a time, but that 
would defeat some of the savings gotten by calculating a delta over
the full filesystem: moves of data over block boundaries would incur 
extra overhead delta's)

Has anybody thought about doing in-place patching of files using
delta's?

Another application where this would do wonders is people that rsync
complete ISO images: they would not need to reserve space for an
entire extra ISO on their systems.

Doei, Arthur. (Wondering if it is at all possible...)

-- 
+- Arthur van Leeuwen, Systems Consultant, arthurvl@xos.nl -+
|  X/OS Experts in Open Systems BV                          |
|  Kruislaan 419                     Phone: +31 20 6938364  |
|  1098 VA  Amsterdam                Fax:   +31 20 6948204  |

Arthur,

I've added Randal Burns to the CC list on this reply.  He has done
a lot of great research on in-place delta updates and will be 
happy to provide further details, I'm sure.  Short summary: You 
can translate a traditional delta to be applied in-place with minor 
loss of compression.

-josh

Quoting Arthur van Leeuwen (arthurvl@xos.nl):
> Hello,
> 
> lately I've been playing with the idea of doing in-place updates 
> of systems using either rsync or xdelta. However, both rsync
> and xdelta seem to be dead set on writing a new file first, and
> then atomically exchanging it with the old file.
> 
> Now, as I want to apply a binary delta to a full filesystem, bigger 
> than the available temporary space, this really makes rsync and
> xdelta extremely tough to use (I could work around it, only updating 
> blocks of half the size of the temporary space at a time, but that 
> would defeat some of the savings gotten by calculating a delta over
> the full filesystem: moves of data over block boundaries would incur 
> extra overhead delta's)
> 
> Has anybody thought about doing in-place patching of files using
> delta's?
> 
> Another application where this would do wonders is people that rsync
> complete ISO images: they would not need to reserve space for an
> entire extra ISO on their systems.
> 
> Doei, Arthur. (Wondering if it is at all possible...)
> 
> -- 
> +- Arthur van Leeuwen, Systems Consultant, arthurvl@xos.nl -+
> |  X/OS Experts in Open Systems BV                          |
> |  Kruislaan 419                     Phone: +31 20 6938364  |
> |  1098 VA  Amsterdam                Fax:   +31 20 6948204  |
-- 
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