superlifter design notes and rZync feedback

Ben Escoto bescoto at
Thu Jul 18 19:49:02 EST 2002

>>>>> "WD" == Wayne Davison <wayned at>
>>>>> wrote the following on Thu, 18 Jul 2002 10:19:40 -0700 (PDT)

  WD> Re: rzync's name cache.  I've revamped it to be a very
  WD> dependable design that no longer depends on lock-step
  WD> synchronization in the expiration of old items (just in the
  WD> creation of new items, which is easy to achieve).

Could you possibly explain this a little more?  I'm not sure I follow
you here with the "expiration of old items" talk.  Or tell me if there
is some basic document I should read that explains all this.  The
rdiff-backup protocol is not sophisticated and certainly has a lot to
gain from these design considerations (not to say that I'll be
motivated enough to do anything about it).

  WD> If we just register the active items that are currently being
  WD> sent over the wire, the name will need to live through the
  WD> entire sig, delta, patch, and (optionally) source-side-delete
  WD> steps.  When the files are nearly up-to-date, having only 16 of
  WD> them will, I believe, be overly restrictive.  Part of the
  WD> problem is that the buffered data on the sig-generating side
  WD> delays the source-side-delete messages quite a bit.  If we had a
  WD> high-priority delete channel, that would help to alleviate
  WD> things, but I think you'll find that having several hundred
  WD> active names will be a better lower limit in your design
  WD> thinking.

For what it's worth, if I understand what you mean by "active names"
correctly, I believe rdiff-backup's protocol can sometimes have
hundreds of active names.

Ben Escoto

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