MD5(Timestamp+message)

I strongly suggest that you keep the timestamps outside of (separate from) whichever digest function you use. Digests are inherently unorderable with respect to time.

The open part of the question is: which shortcuts I can apply to avoid exchanging full lists of messages?

In the following assume: messageNo is a monotonically increase number from oldest to newest; messageId is timestamp+digest[+deviceId+deviceId].

  1. Swap counts; same and you're done.
  2. Otherwise; swap messageId of the message at messageNo (smaller count/2) from the beginning.
  3. Same; add (smaller count/4) to previous messageNo (smaller count/2) and exchange messageIds. goto step 3.
  4. Different; subtract (smaller count/4) from previous messageNo and exchange messageIds. goto step 3.

Basically; do a binary search (oldest->newest) to locate the first difference; and then move forward from that point; exchanging first messageIds; then full messages if needed.

With the rise and rise of 'Social' network sites: 'Computers are making people easier to use everyday'
Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error.
"Science is about questioning the status quo. Questioning authority".
In the absence of evidence, opinion is indistinguishable from prejudice.
I'm with torvalds on this Agile (and TDD) debunked I told'em LLVM was the way to go. But did they listen!

In reply to Re^3: [OT] Merging messages between users on different machines by BrowserUk
in thread [OT] Merging messages between users on different machines by Anonymous Monk

Title:
Use:  <p> text here (a paragraph) </p>
and:  <code> code here </code>
to format your post, it's "PerlMonks-approved HTML":


  • Posts are HTML formatted. Put <p> </p> tags around your paragraphs. Put <code> </code> tags around your code and data!
  • Titles consisting of a single word are discouraged, and in most cases are disallowed outright.
  • Read Where should I post X? if you're not absolutely sure you're posting in the right place.
  • Please read these before you post! —
  • Posts may use any of the Perl Monks Approved HTML tags:
    a, abbr, b, big, blockquote, br, caption, center, col, colgroup, dd, del, details, div, dl, dt, em, font, h1, h2, h3, h4, h5, h6, hr, i, ins, li, ol, p, pre, readmore, small, span, spoiler, strike, strong, sub, summary, sup, table, tbody, td, tfoot, th, thead, tr, tt, u, ul, wbr
  • You may need to use entities for some characters, as follows. (Exception: Within code tags, you can put the characters literally.)
            For:     Use:
    & &amp;
    < &lt;
    > &gt;
    [ &#91;
    ] &#93;
  • Link using PerlMonks shortcuts! What shortcuts can I use for linking?
  • See Writeup Formatting Tips and other pages linked from there for more info.