# 5 Technical

This chapter provides an overview of technical details of the mlr3 framework.

Parallelization

At first, some details about Parallelization and the usage of the future are given. Parallelization refers to the process of running multiple jobs simultaneously. This process is employed to minimize the necessary computing power. Algorithms consist of both sequential (non-parallelizable) and parallelizable parts. Therefore, parallelization does not always alter performance in a positive substantial manner. Summed up, this sub-chapter illustrates how and when to use parallelization in mlr3.

Database Backends

The section Database Backends describes how to work with database backends that mlr3 supports. Database backends can be helpful for large data processing which does not fit in memory or is stored natively in a database (e.g. SQLite). Specifically when working with large data sets, or when undertaking numerous tasks simultaneously, it can be advantageous to interface out-of-memory data. The section provides an illustration of how to implement Database Backends using of NYC flight data.

Parameters

In the section Parameters instructions are given on how to:

• define parameter sets for learners
• undertake parameter sampling
• apply parameter transformations

For illustrative purposes, this sub-chapter uses the paradox package, the successor of ParamHelpers.

Logging and Verbosity

The sub-chapter on Logging and Verbosity shows how to change the most important settings related to logging. In mlr3 we use the lgr package.

Transition Guide

Lastly, we provide a Transition Guide for users of the old mlr who want to switch to mlr3.