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Re: [ftpbench] Wrapper for poll()

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  • shane@time-travellers.org
    ... Yeah, okay. Next time I m in the U.S. (or the next time you re in Amsterdam) we can hook up. We ll bring a laptop to the bar. ;) ... Yeah okay. I
    Message 1 of 6 , Aug 18, 2000
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      On Fri, 18 Aug 2000, Zach Brown wrote:

      > you're on :) I honestly don't care what the result of this
      > 'experiment' would be, I just want to see either of us try and drink
      > that much tequila :)

      Yeah, okay. Next time I'm in the U.S. (or the next time you're in
      Amsterdam) we can hook up. We'll bring a laptop to the bar. ;)

      > > I guess I just don't get this. Why would a signal mechanism be any more
      > > efficient than a poll() mechanism at I/O? Is the idea to establish an
      > > I/O buffer shared by the user process and kernel, and use that to avoid
      > > the extraneous copy on read or write operations (this would be nice)?
      > It gives you light weight event notification. each poll() call you're
      > forced to tell the kernel about what you're interested in. That's
      > expensive. With the signal stuff you register a process that should
      > receive a signal when a descriptor has work to do. You then get a queue
      > of these signals for lots of fds..

      Yeah okay. I guess this could seriously affect you if you had a lot of
      connections waiting a long time for data to show up - as is the case in an
      SQL server. I can easily imagine the worst case: a corporation with
      50,000 SQL connections open, with only 50 performing a query at any given
      time, which still maxes out disk and network I/O for long periods of time.


      (Of course, these folks should probably consider a different architecture,
      but they probably weren't expecting this behavior when the salesmen told
      them how great their centralized database would be.)

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