[R] Which CRAN mirror is the fastest ?

[Barry Rowlingson]

2009/7/30 Uwe Ligges <ligges at statistik.tu-dortmund.de>:

> Hard to lee, you have to try out, I fear.
>
> The speed you see highly depends on the connection from your country to
> others, but of course, there are also some mirrors that are not the fastest
> themselves.

I figured you could write a function that got the CRAN mirror list and
tested their response. Here's my 'cranometer':

cranometer <- function(ms = getCRANmirrors(all = FALSE, local.only = FALSE)){

  dest = tempfile()

  nms = dim(ms)[1]
  ms$t = rep(NA,nms)
  for(i in 1:nms){
    m = ms[i,]
    url = paste(m$URL,"/src/base/NEWS",sep="")
    t = try(system.time(download.file(url,dest),gcFirst=TRUE))
    if(file.exists(dest)){
      file.remove(dest)
      ms$t[i]=t['elapsed']
    }else{
      ms$t[i]=NA
    }
  }
  return(ms)
}

 It works by downloading the latest NEWS file (376Kbytes at the
moment, so not huge) from each of the mirror sites in the CRAN mirrors
list. If you want to test it on a subset then call getCRANmirrors
yourself and subset it somehow.

 I'm running it now on the full CRAN list and I've yet to find a
timeout or error so I'm not sure what will happen if download.file
fails. It retuns a data frame like you get from getCRANmirrors but
with an extra 't' column giving the elapsed time to get the NEWS file.

 CAVEATS: if your network has any local caching then these results
will be wrong, since your computer will probably be getting the
locally cached NEWS file and not the one on the server. Especially if
you run it twice. Oh, I should have put cacheOK=FALSE in the
download.file - but even that might get overruled somewhere. Also,
sites may have good days and bad days, good minutes and bad minutes,
your network may be congested on a short-term basis, etc etc.

 Other ideas: how about combining the CRAN list with my geonames
package to work out distances from where you are to the CRAN site? I
might write that later if I get a minute...

Barry