block check sum sizing

[Chris Shoemaker]

On Mon, Jun 14, 2004 at 01:35:28PM -0400, Wallace Matthews wrote:
> When I dont specify --block-size but have --write-batch=xxx, I get a xxx.rsync_csum file that is 76 Kbytes in size.
> The size of the file varies as the size of the "reference" file is varied. --stats showed matched data that is roughly 6 block lengths
> based on the square root of the newer file. 
> 
> I copy the original data back to the target directory so that I can repeat the experiment. 
> I compute a block size that is the square root of the size of the "reference" file and use --block-size= the computed size.
> The xxx.rsync_csum file is 12 K bytes in size. The xxx.rsync_delta file is the size of the newer file and --stats shows 0 for matched data.
> 
> I copy the original data back to the target directory. 
> I vary the block size to half the previous example. I rerun the experiment. The xxx.rsync_csum file is still 12 K bytes in size. The xxx.rsync_delta file is still the size of the newer file and --stats shows 0 for matched data.
> 
> This is non intuitive. If I got 6 matched blocks when the square root is 181,272 then I would expect to get 6 matched blocks when I specify --block-size = 181,272 and 12 when --block-size is 90636. 
> 
> I would also expect to see xxx.rsync_csum size to double when I divide the blocksize by 2.
> 
> What am I missing??

I don't know.  Are you sure you accurately know the block size used when
no block size is forced?  Did you add some output to show the block size
used?  What if you double the block size?  Is there any choice of block
size that induces changes in the size of xxx.rsync_csum and the --stats
matched data?

-chris

> 
> wally
> 
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