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

[Doug Robinson]

Folks:

When using rsync to copy huge amounts of data I've found that a significant
amount of time is spent computing the checksums.  Sometimes hours, ...
sometimes days - it depends on the total amount of data checked!  And after
that sometimes it's only a few files that need to be updated.

I've pulled the latest git (rsync-3.1.1pre1) and didn't see anything to
address this (or I missed it?).

I was wondering what folks thought of a proposal to enhance rsync to be
able to create and maintain a cache of {filePath, 64-bit mtime, checksum}
beforehand on both source and target systems and then use that cache later
on when asked to sync the two systems together?  Then cache entry
validation would be a quick stat64() to make sure that the 64-bit mtime
didn't change before sending the checksum over the wire for comparison.

Clearly the cache would need to be completely invalidated (or re-created)
if the file system became corrupt.  That could be handled via an "rm -rf"
of the cache.

Thoughts?

Thank you.

Doug
--
WANdisco // *Non-Stop Data*

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e. doug.robinson at wandisco.com

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