On 12/04/11 01:58, Evan Rempel wrote:
I am looking at add some code to the rsync tool but want to
know if I am "totally out to lunch".
I realize that my example is so trivial that I am sure I will
get replies of "don't do it that way", but bear in mind
that it is just an example, and there are real world cases
where I think this functionality would be useful.
I am trying to figure out if rsync can do something like
cat myfile.dat | rsync - remoteHost:/some/path/myfile.dat
which would take a stream of data and send/store it onto the
remote host.
Not possible with rsync (as far as I know), but is possible with
librsync (which is a completely different code base than rsync itself).
My questions is more about "can the rsync algorithm
do this?".
As far as I can tell, you need two passes on one end (either the
receiving or the sending). There is no reason for the other end to be
completely one pass.
Technically, the question boils down to "Is rsync a single pass
algorithm, or is it a multi-pass algorithm?"
If it is a single pass algorithm then all is good.
If it is a multi-pass algorithm then how big of a buffer does it
need to perform the passes?
The definition of "one pass" is "can be performed with one reading of
the file and a O(1) buffer". If you can answer the question, then it is,
by definition, one pass.
Namely, is it a block by block multi-pass,
or is it a complete file/object multi-pass algorithm.
Again, the question is meaningless. If you can apply an algorithm one
block at a time, then it's one pass by definition.
Shachar
--
Shachar Shemesh
Lingnu Open Source Consulting Ltd.
http://www.lingnu.com
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