At 21:45 -0700 29/07/08, Robert O'Callahan wrote:
On Tue, Jul 29, 2008 at 11:20 AM, Dave Singer
<<mailto:[EMAIL PROTECTED]>[EMAIL PROTECTED]> wrote:
Caching is on a full URL basis, of course. Once that is decided,
then yes, I think that pre-cached items for a given URL are in the
general cache for that site.
A site that uses this feature is likely to be fragile. It will have
to have z.html both in the archive and available directly from the
server, in case z.html is requested before the load of the archive
has finished.
No. The definition *for MPEG-21 files* (which is all I have
specified so far) is that accesses to the matching absolute URL (or
relative URL) from within the archibe MUST find the resource within
the archive. Since, as I say, this format starts with a directory,
you know whether you have it or not. If ZIP or JAR files don't have
a directory, then yes, they have a different trade-off and must load
the whole thing before they know.
You only need a resource *outside* the archive if it is requested
'nakedly' from outside the archive. If you do that, it might indeed
hurt, but that's your choice as a site.
The performance trade-off is very simple; if you have many small
resources it may be much more efficient to ftch them as a package
than individually. The downside is that this is a single connection
in a pre-defined order whereas multiple resources could be fetched on
parallel connections, and as needed. I doubt more connections to the
same server gets you more bandwidth, however, and the mpeg-21 format
also allows extent-based interleaving so that e.g. a lareg HTML page
and and large JPEG can be loaded progressively together.
And if those copies ever get out of sync you're in very big trouble,
because depending on the context, either the archive version or the
direct version is likely to consistently win the load race, so just
occasionally some clients will get the wrong version. This seems
like a highly error-prone design.
Rob
--
"He was pierced for our transgressions, he was crushed for our
iniquities; the punishment that brought us peace was upon him, and
by his wounds we are healed. We all, like sheep, have gone astray,
each of us has turned to his own way; and the LORD has laid on him
the iniquity of us all." [Isaiah 53:5-6]
--
David Singer
Apple/QuickTime
