Re: rsync and streaming replication

2011/11/14 Scott Ribe <scott_ribe(at)elevated-dev(dot)com>:
> On Nov 14, 2011, at 10:59 AM, Jean-Armel Luce wrote:
>
>> just for the value : rsync --checksum is the option to use to prevent
>> copying of identical files
>
> No, that's not what it's used for. It already avoids sending identical blocks by using checksums. --checksum forces a checksum on files that have identical sizes & mod times, thus catching files that have different contents despite having the same mod times & sizes.

no, you are wrong.
-c, --checksum
"This changes the way rsync checks if the files have been changed and
are in need of a transfer. Without this option, rsync uses a "quick
check" that (by default) checks if each file's size and time of last
modification match between the sender and receiver. This option
changes this to compare a 128-bit checksum for each file that has a
matching size. Generating the checksums means that both sides will
expend a lot of disk I/O reading all the data in the files in the
transfer (and this is prior to any reading that will be done to
transfer changed files), so this can slow things down significantly. "
...

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