[Bug 10380] New: Non-Nested Folder Optimisation

[Perry Smith]

I may be missing the point but the contents of a file within a directory can 
change without affecting the directory.

> ls -ld . dog
> drwxrwxrwt  24 root    wheel  816 Jan 14 11:39 .
> -rw-rw-r--   1 pedzan  wheel    0 Jan 14 11:41 dog
> 
> echo more >> dog
> 
> ls -ld . dog
> drwxrwxrwt  24 root    wheel  816 Jan 14 11:39 .
> -rw-rw-r--   1 pedzan  wheel    5 Jan 14 12:39 dog

dog changed.  Its timestamp changed.  But the containing
directory's timestamp did not.  This is on a Mac but I think
this is generally true.  If you add or delete a file, the directory's
modified time changes but not if the files within it change.

On Jan 14, 2014, at 11:22 AM, samba-bugs at samba.org wrote:

> https://bugzilla.samba.org/show_bug.cgi?id=10380
> 
>           Summary: Non-Nested Folder Optimisation
>           Product: rsync
>           Version: 3.1.0
>          Platform: All
>        OS/Version: All
>            Status: NEW
>          Severity: enhancement
>          Priority: P5
>         Component: core
>        AssignedTo: wayned at samba.org
>        ReportedBy: me at haravikk.com
>         QAContact: rsync-qa at samba.org
> 
> 
> One handy feature of most (all?) unix file systems is that if the contents of a
> folder are changed, then the folder's modified time will be updated as well,
> which presents an opportunity for optimised comparisons.
> 
> Quite simply, if a folder's modified time is the same as the corresponding
> folder in the destination, then no comparison of its contents needs to be
> performed.
> At least, that is true if the folder doesn't contain any nested folders, as
> modifications to these do not affect the parent folder's modified time.
> 
> What I would like to propose is that when rsync begins generating a file list
> for a destination directory, that it should attempt to mark any directories
> that do no contain nested directories. When it comes time to compare such a
> directory, the comparison can be done using only the modified times (if rsync
> is operating in that mode), and only needs to compare file lists if these times
> differ. Provided rsync is able to generate enough of the destination file-list
> in advance, then this should allow many unchanged folders to be skipped in
> their entirety, without having to delve further into their contents.
> 
> This feature could be enhanced by the use of a metadata file (see bug 10379) by
> storing a flag in a destination folder if it contains no nested directories.
> This way, so long as the metadata file is valid, there is no need to process
> the directory's file-list before an optimised comparison is performed.
> 
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