[SAGA-RG] missing(?) method reporting last modification time

[Thilo Kielmann]

John,

what would be the special thing with a timestamp and everything else,
like file size, content, permissions... that we all have already?

Thilo

On Fri, May 29, 2009 at 06:21:40AM -0700, John Shalf wrote:
> Cc: saga-rg at ogf.org
> From: John Shalf <jshalf at lbl.gov>
> To: Thilo Kielmann <kielmann at cs.vu.nl>
> Subject: Re: [SAGA-RG] missing(?) method reporting last modification time
> 
> For the async version of the SAGA interface, what consistency model to  
> you propose for the modification time information?  POSIX semantics do  
> not address this, which is precisely why POSIX is so damned slow on  
> distributed/remote filesystems.  It seems we'd need to at least  
> propose an unambiguous consistency model for the time-stamps and how  
> this would interact with concurrent async read/write calls that might  
> be in progress.
> 
> (just making the consistency model based on current state at the  
> remote side is fine, but from the client side, you might end up with  
> absurd situations when you do an async timestamp request concurrent  
> with an async file open for example.)
> 
> -john
> 
> On May 29, 2009, at 6:15 AM, Thilo Kielmann wrote:
> >Folks,
> >
> >within our group we are currently delving into issues with accessing
> >remote file systems. What strikes us is that such access is SLOW.
> >As such, it would be very beneficial if one could find out when (and
> >thus whether) a remote file or directory has been modified.
> >
> >While returning this piece of information sounds to be "trivial", it  
> >strikes
> >us that the SAGA spec has no such call in the name space package  
> >(where files
> >reside).
> >
> >In POSIX terms, this is the info returned by the stat system call
> >(see: man 2 stat), with the st_mtime parameter.
> >
> >In Java, files have a method lastmodified().
> >
> >Both POSIX and Java report the time in milliseconds since 01/01/1970  
> >(epoch).
> >
> >
> >Of course, it looks like nobody has ever been thinking about such a  
> >use case,
> >but here we are! Our feeling is that the last modification time is  
> >very
> >essential meta data about files, so such a call should certainly be  
> >there.
> >With our current problem certainly not being the only use case for  
> >finding
> >out how old/new a given file or directory is...
> >
> >Our favourite proposal is to add a method that returns the last  
> >modification
> >time to both ns_entry and ns_directory as this makes sense with  
> >physical as
> >well as with logical (replicated) files.
> >
> >
> >Any reactions/objections ???
> >
> >
> >Thilo Kielmann
> >-- 
> >Thilo Kielmann                                 
> >http://www.cs.vu.nl/~kielmann/
> >--
> > saga-rg mailing list
> > saga-rg at ogf.org
> > http://www.ogf.org/mailman/listinfo/saga-rg
> 



-- 
Thilo Kielmann                                 http://www.cs.vu.nl/~kielmann/