variable lookups possible?

[Fairlight]

On Wed, Jul 21, 2004 at 02:32:28PM -0400, Walter Vaughan may or may not have
proven themselves an utter git by pronouncing:
> Fairlight wrote:
> > I now believe that I can make the pseudo-RSS parsing module a reality
> 
> How does this add any fuctionality that rsync doesn't already offer?
> Interesting minds want to know.

Glad you asked.  I just went through the man page for rsync again to make
sure, (rsync 2.5.6 protocol 26)

Basically the docs even claim it's basically just a fancy replacement for
rcp that can use multiple transport layers.

The problem with this is that it has no way to let fP know that it may be
working on the file (ie., it may be only partially copied/diff'd at any
given point during its execution).

In short, you could end up working with a corrupt table if you hit
something at the wrong time.  The docs for rsync make zero mention of any
sort of file locking options or functionality.  Every search for 'lock'
only referred to blocking/non-blocking I/O, or the block size.  In short, I
think it's unsafe for use during fP's continued operation, and you couldn't
really rely on this without making fP inaccessible via some downtime with
httpd, or via code that checks for a lockfile that's created/removed by a
wrapper around rsync, etc.

My plan makes it more transactional, where you use fP itself to make any
changes using its own mechanisms, thus relying on its own locking to make
sure nothing is currently unusable.  You're also never actually mangling
the disk layer by altering the file itself.  So Bill Vermillion's trick of
pre-expanding files and letting them sit and just fill up so they never
fragment would still work, whereas I suspect rsync may defeat that scheme.

Yes, you could rsync more than nightly, or even a few times a day.  But as
you do, your chances of colliding would naturally go up.  :(

This avoids all of that.

mark->
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