Return-Path: william@bourbon.usc.edu
Delivery-Date: Mon Nov 17 09:15:17 2008
X-Spam-Checker-Version: SpamAssassin 3.2.3 (2007-08-08) on merlot.usc.edu
X-Spam-Level: 
X-Spam-Status: No, score=-2.4 required=5.0 tests=AWL,BAYES_00 autolearn=ham
	version=3.2.3
Received: from bourbon.usc.edu (bourbon.usc.edu [128.125.9.75])
	by merlot.usc.edu (8.14.1/8.14.1) with ESMTP id mAHHFH6Y004240
	for <cs551@merlot.usc.edu>; Mon, 17 Nov 2008 09:15:17 -0800
Received: from bourbon.usc.edu (localhost.localdomain [127.0.0.1])
	by bourbon.usc.edu (8.14.2/8.14.1) with ESMTP id mAHHBnTW024667
	for <cs551@merlot>; Mon, 17 Nov 2008 09:11:49 -0800
Message-Id: <200811171711.mAHHBnTW024667@bourbon.usc.edu>
To: cs551@merlot.usc.edu
Subject: Re: Store question
Date: Mon, 17 Nov 2008 09:11:48 -0800
From: Bill Cheng <william@bourbon.usc.edu>

Someone wrote:

  >      Upon your comments about STORE message below, I conclude that when 
  > receiving STORE message, the node doesn't need to check if it already 
  > has a copy of the file. Because it's impossible since the nonce must be 
  > different.

Correct.

  >      What about when forwarding GET message? I think after it flips the 
  > coin and decides to cache the file, it needs to check if it already has 
  > a copy of the file, correct?

Correct.

  >      If it is correct, besides forwarding GET message and receiving GET 
  > message, is there any other situation we need to check if it already has 
  > a copy of the file?

I cannot think of anything at this point.  If you see a
situation where it needs to be done, then you need to write
code for it.
--
Bill Cheng // bill.cheng@usc.edu <URL:http://merlot.usc.edu/william/usc/>





  Bill Cheng wrote:
  > Someone wrote:
  > 
  >   > Had a few doubts on the store feature ...
  >   > Is it possible for the same file to be stored twice on the
  >   > network?
  > 
  > Yes.
  > 
  >   > Seems possible so when I get a store response on a node
  >   > I need to check if the file already exists on the node before
  >   > storing it (in the Cache area).
  > 
  > You don't need to check if you already has a copy of the file
  > if you are just caching it.  (Of course, you need check if
  > you have seen the *message* by looking at the message UOID
  > and discard duplicate messages -- this is what you do for
  > messages of all types anyway.)
  > 
  >   > While matching should the
  >   > filename and the SHA value be enough or should we match the
  >   > keywords also ?
  > 
  > No.  FileName, SHA1, *and* Nonce.
  > 
  >   > Should we consider the files to be different if
  >   > they have the same name and content but different keywords ?
  > 
  > Just FileName, SHA1, *and* Nonce.  If the keywords are
  > different for the same file, Nonce must also be different!
  > 
  >   > If I already have the file do I still need to probabilistically
  >   > flood it ?
  > 
  > Yes.  You should *not* even be checking if you have the
  > file already if you are forwarding a file.
  > --
  > Bill Cheng // bill.cheng@usc.edu <URL:http://merlot.usc.edu/william/usc/>