rsync - Dec 2009 - DO NOT REPLY [Bug 6946] New: Enable timestamp comparison with multiple file owners

https://bugzilla.samba.org/show_bug.cgi?id=6946

           Summary: Enable timestamp comparison with multiple file owners
           Product: rsync
           Version: 3.1.0
          Platform: Other
        OS/Version: Linux
            Status: NEW
          Severity: enhancement
          Priority: P3
         Component: core
        AssignedTo: wayned at samba.org
        ReportedBy: james at phsys.co.uk
         QAContact: rsync-qa at samba.org


Currently if multiple users using group write permissions update the same
folder then they can't always update file timestamps. This is because the
file
may be owned by a separate user. Furthermore, changing the timestamp may be
undesirable if files are being updated from various sources, since timestamps
moving backwards can confuse some software.

Disabling timestamp updates does not impair rsync's functionality but it can
severely reduce performance. It is forced to fully read each file, on both
sides of the transfer, in order to obtain a checksum.

I propose caching these checksums, against a file's timestamp, in order to
avoid this performance problem. This method does not require an update of the
file's timestamp. It would require a database of some sort linking files and
timestamps to the calculated checksum. Whenever a file's timestamp changed,
the
checksum would need recalculating.

To operate efficiently this would need to operate at both sides of the
connection. Basically instead of reading a file to determine its timestamp the
cache would first be checked. If the cache did not contain a timestamp then it
would be calculated and stored in the cache for future reference.

I'd suggest specifying the cache location for local and remote connections
via
a parameter initially.

I intend to have a go at adding this functionality myself, although I'd be
very
interested to hear any comments. Also if anyone has done anything similar, or
if I am missing some simpler solution to this problem.


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https://bugzilla.samba.org/show_bug.cgi?id=6946





------- Comment #1 from matt at mattmccutchen.net  2009-12-05 00:32 CST -------
Note that several of the maintained patches have to do with checksum caching:
the ones with "checksum" in the name as well as "db.diff". 
See the bottom of
http://rsync.samba.org/download.html for how to access these patches.


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