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

Josh MacDonald jmacd at CS.Berkeley.EDU
Thu May 23 07:32:01 EST 2002


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.


Quoting Arthur van Leeuwen (arthurvl at
> 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 at -+
> |  X/OS Experts in Open Systems BV                          |
> |  Kruislaan 419                     Phone: +31 20 6938364  |
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