[R] foreach performance

[Dom Pazzula]

I'm noticing a huge performance hit when using foreach with doSNOW.  Any ideas on why the parallel loop runs ~8 times slower than the same foreach run sequentially?
 
> require(doSNOW)
Loading required package: doSNOW
Loading required package: foreach
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Loading required package: iterators
Loading required package: snow
> cl = makeSOCKcluster(rep("localhost",3))
> registerDoSNOW(cl)
> 
> system.time((
+ x = foreach(i=seq(1,5000)) %dopar% {
+     arima.sim(n = 250, list(ar=c(0.8897, -0.4858), ma=c(-0.2279, 0.2488)),
+         rand.gen = function(n, ...) sqrt(0.1796) * rt(n, df = 5))
+ }
+ ))
   user  system elapsed 
   4.46    0.22   50.27 
> 
> system.time((
+ y= foreach(i=seq(1,5000)) %do% {
+     arima.sim(n = 250, list(ar=c(0.8897, -0.4858), ma=c(-0.2279, 0.2488)),
+         rand.gen = function(n, ...) sqrt(0.1796) * rt(n, df = 5))
+ }
+ ))
   user  system elapsed 
   6.25    0.01    6.27 
> system.time((
+ for (i in seq(1,5000)) {
+ x = arima.sim(n = 250, list(ar=c(0.8897, -0.4858), ma=c(-0.2279, 0.2488)),
+         rand.gen = function(n, ...) sqrt(0.1796) * rt(n, df = 5))
+ }
+ ))
   user  system elapsed 
   2.76    0.00    2.76 


Dominic J. Pazzula
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dompazz at yahoo.com