Unreal Engine projects take too long to build from Rider

Problem

When executing an Unreal Engine project build from Rider, one can encounter build performance issues. Rider will take more time to build the project compared to building the same project from CLI.

Cause

Often, this problem stems from the limit of the worker threads spawned by Unreal Build Tool (UBT). Before initiating the project build, UBT checks for available memory to determine the number of build worker threads. It calculates the number of worker threads Free RAM in bytes by the MemoryPerActionBytes value. The default value assigned to MemoryPerActionBytes is 1.5 GiB.

Resolution

Increasing the machine's physical memory is the quickest way to improve the build performance.

If the target system has a lot of swap available on a fast storage device, the build speed can be optimized by either reducing the MemoryPerActionBytes value or disabling this check completely using the value 0. This can be achieved by modifying <MemoryPerActionBytes> value located in the BuildConfiguration.xml. The following snippet illustrates how the memory check can be deactivated:

<ParallelExecutor>
  <MemoryPerActionBytes>0</MemoryPerActionBytes>
</ParallelExecutor>

Here's how BuildConfiguration.xml without any other options might look like:

<?xml version="1.0" encoding="utf-8" ?>
<Configuration xmlns="https://www.unrealengine.com/BuildConfiguration">
	<ParallelExecutor>
		<MemoryPerActionBytes>0</MemoryPerActionBytes>
	</ParallelExecutor>
</Configuration>