From mboxrd@z Thu Jan  1 00:00:00 1970
To: 9fans@cse.psu.edu
Subject: Re: [9fans] venti block score & type
In-Reply-To: Your message of "Thu, 11 Dec 2003 20:05:10 PST."
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From: "Russ Cox" <rsc@swtch.com>
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Date: Thu, 11 Dec 2003 23:25:49 -0500
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> > > Similarly, that attempting to write a block whose score is already in
> venti,
> > > but with a different type, will fail?
> >
> > No.  A new index entry will be written for the new type.
> >
> > Types are really just to help a little in interpreting the
> > data.  They're almost purely advisory.  (Almost, because
> > the answer to your first question is yes.)  Since blocks are
> > zero-truncated before storing, the zero-length block
> > might reasonably be interpreted as a data block or as
> > a pointer block of any depth.  Similarly, if I store a file
> > whose contents are the SHA1 hash of a small file, that
> > contents will be stored as data, but storing the small file
> > itself would use the same block as a first-level pointer
> > block.
>
> So venti stores a list of types written for each score?  Thus reading a
> block would require that the type be in that list, but writing a block would
> add the type to the list if it was not already present?

Sure, that would be one way.

In the current Venti server, writing a block with
a new type adds a whole new (score, type) index
entry.    The index entries only have one type,
not a list.

Russ