[RFC] dynamic checksum size

jw schultz jw at pegasys.ws
Mon Mar 24 03:46:44 EST 2003

On Mon, Mar 24, 2003 at 01:02:28AM +1100, Donovan Baarda wrote:
> On Mon, Mar 24, 2003 at 12:54:26AM +1100, Donovan Baarda wrote:
> > On Sun, Mar 23, 2003 at 03:46:34AM -0800, jw schultz wrote:
> > > On Sun, Mar 23, 2003 at 05:45:47PM +1100, Donovan Baarda wrote:
> > > > On Sun, 2003-03-23 at 07:40, jw schultz wrote:
> A thought occurred to me after writing this; a viable blocksize heuristic is
> just a fixed block size. This makes the signature size almost proportional
> to the filesize, except for the growth in blocksum size.
> I don't necisarily advocate it though. I think increasing the blocksize is a
> good idea as files grow because file and signature size also contribute to
> CPU load.

There are a number of cases where a fixed block size makes
sense, but they are entirely dependant on content.
Generally they will be files where the data is block
oriented, block aligned, and subject to reordering.

Filesystem images (ISO leaps to mind) would probably benefit
from an rsync block size that is a multiple of the
filesystem block size.  Oracle tablespaces might make sense
to have a rsync block size that corresponds to the block
size used by Oracle.  This is why i said that DBAs would
gripe if the option were absent. 

	J.W. Schultz            Pegasystems Technologies
	email address:		jw at pegasys.ws

		Remember Cernan and Schmitt

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