I finally found the time to try parallel computing in R using snowfall/snow thanks to this article in the first issue of the R Journal (replacement of R News). I didn’t try parallel computing before because I didn’t have a good toy example, and it seemed like a steep learning curve. Snow and Snowfall is perfect for ‘embarrassingly parallel’ jobs, eg, a simulation study, bootstrap, or a cross-validation. I do simulation studies a lot, eg, assessing the properties of a statistical methodology, so implementing parallel computing will be very useful.

I got the toy example to work, but it was parallel on a single computer with multiple cores. Thanks to Michael Zeller, I got it to work on multiple machines. If we use multiple nodes, make sure we enable passwordless ssh.

Credit for getting snowfall to work on the BDUC servers (uci-nacs) goes to Harry Mangalam.

Here is a script, with a few examples:

 <pre class="src src-sh"><span style="color: #ff4500;">## </span><span style="color: #ff4500;">Example 1 - Multi-core on a single computer</span>

sink(‘SnowFallExample.Rout’, split=TRUE) .Platform .Machine R.version Sys.info()

library(snowfall) # 1. Initialisation of snowfall. # (if used with sfCluster, just call sfInit()) sfInit(parallel=TRUE, cpus=2)

# 2. Loading data. require(mvna) data(sir.adm) # 3. Wrapper, which can be parallelised. wrapper <- function(idx) { # Output progress in worker logfile cat( “Current index: “, idx, “\n” ) index <- sample(1:nrow(sir.adm), replace=TRUE) temp <- sir.adm[index, ] fit <- crr(temp$time, temp$status, temp$pneu) return(fit$coef) } # 4. Exporting needed data and loading required # packages on workers. sfExport(“sir.adm”) sfLibrary(cmprsk)

# 5. Start network random number generator # (as “sample” is using random numbers). sfClusterSetupRNG() # 6. Distribute calculation

start <- Sys.time(); result <- sfLapply(1:1000, wrapper) ; Sys.time()-start # Result is always in list form. mean(unlist(result)) # 7. Stop snowfall sfStop()

## Example 2 – Multiple nodes on a cluster (namely, the family-guy cluster at uci-ics) sink(‘SnowFallExample.Rout’, split=TRUE) .Platform .Machine R.version Sys.info()

library(snowfall) # 1. Initialisation of snowfall. # (if used with sfCluster, just call sfInit()) sfInit(socketHosts=rep(c(‘peter-griffin.ics.uci.edu’,‘stewie-griffin.ics.uci.edu’, ‘neil-goldman.ics.uci.edu’, ‘mort-goldman.ics.uci.edu’,‘lois-griffin.ics.uci.edu’),each=2), cpus=10,type=‘SOCK’,parallel=T)

# 2. Loading data. require(mvna) data(sir.adm) # 3. Wrapper, which can be parallelised. wrapper <- function(idx) { # Output progress in worker logfile cat( “Current index: “, idx, “\n” ) index <- sample(1:nrow(sir.adm), replace=TRUE) temp <- sir.adm[index, ] fit <- crr(temp$time, temp$status, temp$pneu) return(fit$coef) } # 4. Exporting needed data and loading required # packages on workers. sfExport(“sir.adm”) sfLibrary(cmprsk)

# 5. Start network random number generator # (as “sample” is using random numbers). sfClusterSetupRNG() # 6. Distribute calculation

start <- Sys.time(); result <- sfLapply(1:1000, wrapper) ; Sys.time()-start # Result is always in list form. mean(unlist(result)) # 7. Stop snowfall sfStop()

## Example 3 – Multiple nodes on a cluster (namely, the BDUC servers of uci-ics) ## ssh to bduc, then ssh to one of their claws (the head node is 32bit whereas the other wones are 64) ## put something like ## export LD_LIBRARY_PATH=/home/vqnguyen/lib:/usr/local/lib:/usr/lib:/lib:/sge62/lib/lx24-x86 in .bashrc ## or ## Sys.setenv(LD_LIBRARY_PATH=”/home/vqnguyen/lib:/usr/local/lib:/usr/lib:/lib:/sge62/lib/lx24-x86″) ## in an R session. Note: modify path to your home directory ## might have to install required packages elsewhere, like ~/Rlib, and use .libPaths() to add library path. Put this in .Rprofile sink(‘SnowFallExample.Rout’, split=TRUE) .Platform .Machine R.version Sys.info()

# 1. Initialisation of snowfall. # (if used with sfCluster, just call sfInit()) library(snowfall) sfInit(socketHosts=rep(c(‘claw1′, ‘claw2′),each=4), cpus=8,type=‘SOCK’,parallel=T)

# 2. Loading data. require(mvna) data(sir.adm) # 3. Wrapper, which can be parallelised. wrapper <- function(idx) { # Output progress in worker logfile cat( “Current index: “, idx, “\n” ) index <- sample(1:nrow(sir.adm), replace=TRUE) temp <- sir.adm[index, ] fit <- crr(temp$time, temp$status, temp$pneu) return(fit$coef) } # 4. Exporting needed data and loading required # packages on workers. sfExport(“sir.adm”) sfLibrary(cmprsk)

# 5. Start network random number generator # (as “sample” is using random numbers). sfClusterSetupRNG() # 6. Distribute calculation

start <- Sys.time(); result <- sfLapply(1:1000, wrapper) ; Sys.time()-start # Result is always in list form. mean(unlist(result)) # 7. Stop snowfall sfStop()

This is a good general reference for snowfall. Next thing to try is getting rpvm (PVM) to work for snowfall!