"I still think a 3 tape sort should be a required early assignment (learn that not everything can fit into memory at once).
TTFN - Guy" Second. Lee C. On Fri, Oct 30, 2015 at 12:15 PM, Guy Sotomayor <g...@shiresoft.com> wrote: > > > On Oct 30, 2015, at 11:35 AM, Paul Koning <paulkon...@comcast.net> > wrote: > > > > > >> On Oct 30, 2015, at 2:16 PM, Noel Chiappa <j...@mercury.lcs.mit.edu> > wrote: > >> > >> ... > >> Apparently nobody had ever told them that a number in memory is... just > a > >> number. At which point it became clear that they needed to know a little > >> more about how a computer actually worked. > > > > That reminds me of an exchange I had with a younger colleague who was > writing a document describing how to do incremental TCP checksum update > correctly. He was tripping over the issue of negative zero. I told him > the answer simply was to subtract the complement with end around borrow. > He didn't believe me and ended up proving it by exhaustively testing every > case. > > > > > My favorite of this class of issues, was when I was working at a startup > doing an embedded product with Linux as the OS. We all had Linux machines > for building/testing. I was responsible for the Linux kernel at the > company. I had someone come up to me and said “the VM system is broken…my > program works fine on my desktop but I keep getting page faults on the > embedded platform”. The conversation was something like this: > Me: So, what’s the program doing memory wise? > Him: I allocate an array of structures and I read them off of disk into > the array. > Me: How big are the structures? > Him: About 4K > Me: How many are you allocating? > Him: 100,000 > Me: Rolls eyes. That’s 4GB. We don’t have 4GB on the embedded platform. > You don’t even have that on your workstation. > Him: But it works there and not on the embedded platform. > Me: We don’t have paging turned on in the embedded platform. > Him: Can’t we turn it on? It makes my code so simple! > Me: No! Go allocate a *reasonable* sized array (say 100) and shuffle in > from the disk when the data you need isn’t there. You walk the data > structure mostly sequentially anyway, so there’s no reason to have the > entire file in memory. > > I still think a 3 tape sort should be a required early assignment (learn > that not everything can fit into memory at once). > > TTFN - Guy > > -- Lee Courtney +1-650-704-3934 cell
