Caching {filePath,mtime64,checksum} values to speed up execution-time

Doug Robinson doug.robinson at
Wed Mar 12 13:38:35 MDT 2014


(your reply did finally show up)

On Tue, Mar 11, 2014 at 6:20 PM, Kevin Korb <kmk at> wrote:

> >OK, in that case you should try using --ignore-times instead
>- --checksum.  With --ignore-times rsync will redo the delta transfer of
>all files.  This is usually faster than --checksum and won't cause
>much additional data transfer.
>Unless --whole-file is in play.

If I use --ignore-times then every file will be checksummed via the normal
mechanism (per "").  The point
of my proposal was to prevent all of the checksum work (I/O,CPU) at the time
of copy by pre-computing the whole-file checksums for comparison.  Yes,
this means using the --checksum option, but then most of the work done by
generator and sender in computing block checksums can be skipped at the
time of sync simply by comparing the whole-file checksums and matching.

My goal is to spread out the I/O and CPU intensive portions of the sync to
"before" the actual invocation-to-sync is made.  Cache validation is as I
described - although possibly adding in 64-bit ctime to the mix would catch
even those trying to fake non-modification by reseting the 64-bit mtime (a
trick noted in

That last URL was a find by one of my co-workers.  Now I need to go track
the "db.diff" patch that Wayne notes and see if I can tweak it to do the
stuff and so on.

Thank you.

Doug Robinson

WANdisco // *Non-Stop Data*

t. 925-396-1125
e. doug.robinson at


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