There are a number of concepts and terminologies that are useful to understand in order to use disk.frame effectively.

## What is a disk.frame and what are chunks?

A disk.frame is nothing more a folder and in that folder there should be fst files named “1.fst”, “2.fst”, “3.fst” etc. Each of the “.fst” file is called a chunk.

## Workers and parallelism

Parallelism in disk.frame is achieved using the future package. When performing many tasks, disk.frame uses multiple workers, where each worker is an R session, to perform the tasks in parallel.

It is recommended that you should running these to set-up immediately after you library(disk.frame). For example:

library(disk.frame)
setup_disk.frame()

# this will allow unlimited amount of data to be passed from worker to worker
options(future.globals.maxSize = Inf)

For example, suppose we wish to compute the number of rows for each chunk, we can clearly perform this simultaneously in parallel. The code to do that is

# use only one column is fastest
df[,.N, keep = "first_col"]

or equivalent using the srckeep function

# use only one column is fastest
srckeep(df, "first_col")[,.N, keep = "first_col"]

Say there are n chunks in df, and there are m workers. Then the first m chunks will run chunk[,.N] simultaneously.

To see how many workers are at work, use

# see how many workers are available for work
future::nbrOfWorkers()