On Wed, 16 Oct 2002, Jan Harkes wrote:

> > I see the fact that coda has to download the entire file at once before
> > any reads can take place as a rather serious limitation.  There are many
> > times when only the first part of of a file is read in and the user has no
> > intention of reading the rest of the file.  For example when scanning a
> > directory of JPEGS with previews or Music files for the tag information.  
> > Etc...  The larger the files are the more of an issue this becomes.
> 
> Actually mp3v1 tags are typically at the end of a file, so you'd have to
> wait for the whole file anyways. 

Um no, you can seek to the end of the file and only read the end.

> With mp3v2 it is even worse, because
> tags are allowed to be interspersed anywhere within the file, you
> actually need to read everything to extract all possible tags.

I am do not know any better so I am not going to argue with you.

> It is an application problem, not a filesystem problem. Other
> filesystems do have the same semantics as Coda, for instance a
> hierarchical storage system where files are pulled of a tape by a robot
> if they are not available on disk.

Yes others file systems have the same semantics as Coda but most general 
purpose file systems don't.  With most file systems you can seek anywhere 
in the file and only read part of it.  Applications should not have to 
rework the way they work in order to work around limitations of an of an 
specific file system which does not have the expected behavior of a 
general purpose file system.

> The image viewer I often use does it right, it has the previews in a
> subdirectory '.xvpics', as separate files and as such has no problem.
> Same thing with my mp3 car radio (riocar/empeg player) It stores a
> database of all the tags in a separate file, so that it doesn't have to
> scan through every file on the disk to show a playlist, or do searches.

This approach has its advantages such as not having to seek as much but 
for a general purpose file system reading the first couple of bytes of a 
file is generally not a problem.

> > And when dealing with huge files 1+ Gig files it really matters.  I really
> > don't want to download the entire file just to preview the first couple of
> > seconds.
> 
> If you're only working with blocks of a couple of seconds, split the
> huge 1Gig files in blocks of a couple of seconds, problem solved.

Um that is a lot easier said than done.  Once again this is a workaround 
due to the limits of the Coda file system which I do not think should be 
necessary.

--- 
http://kevin.atkinson.dhs.org