# Runtime Performance

GraalVM optimizes R code that runs for extended periods of time. The speculative optimizations based on the runtime behaviour of the R code and dynamic compilation employed by the GraalVM runtime are capable of removing most of the abstraction penalties incurred by the dynamism and complexity of the R language.

Examine the algorithm in the following example which calculates the mutual information of a large matrix:

```
x <- matrix(runif(1000000), 1000, 1000)
mutual_R <- function(joint_dist) {
joint_dist <- joint_dist/sum(joint_dist)
mutual_information <- 0
num_rows <- nrow(joint_dist)
num_cols <- ncol(joint_dist)
colsums <- colSums(joint_dist)
rowsums <- rowSums(joint_dist)
for(i in seq_along(1:num_rows)){
for(j in seq_along(1:num_cols)){
temp <- log((joint_dist[i,j]/(colsums[j]*rowsums[i])))
if(!is.finite(temp)){
temp = 0
}
mutual_information <-
mutual_information + joint_dist[i,j] * temp
}
}
mutual_information
}
system.time(mutual_R(x))
# user system elapsed
# 1.321 0.010 1.279
```

Algorithms such as this one usually require C/C++ code to run efficiently:^{1}

```
if (!require('RcppArmadillo')) {
install.packages('RcppArmadillo')
library(RcppArmadillo)
}
library(Rcpp)
sourceCpp("r_mutual.cpp")
x <- matrix(runif(1000000), 1000, 1000)
system.time(mutual_cpp(x))
# user system elapsed
# 0.037 0.003 0.040
```

(Uses r_mutual.cpp.)

However, after a few iterations, GraalVM runs the R code efficiently enough to make the performance advantage of C/C++ negligible:

```
system.time(mutual_R(x))
# user system elapsed
# 0.063 0.001 0.077
```

The GraalVM R runtime is primarily aimed at long-running applications. Therefore, the peak performance is usually only achieved after a warmup period. While startup time is currently slower than GNU R’s, due to the overhead from Java class loading and compilation, future releases will contain a native image of R with improved startup.

^{1} When this example is run for the first time, it installs the `RcppArmadillo`

package,which may take a few minutes.
Note that this example can be run in both GraalVM’s R runtime and GNU R.