Slow SBT launch with many projects

Question

I have an SBT project with ~ 40 subprojects. There are several plugins, the largest of which are Play and sbt-native-packager. There are no global plugins.

On some pretty promising equipment, the launch (after the first time) takes 20-25 s. I know that this is not all due to the launch of the JVM, since a small project (net overhead) starts in 3-4 seconds.

How to find out why sbt takes longer to run in a larger project?

I tried sbt -Dsbt.task.timings = true, but it does not include what takes up most of the time. After the last prints of time, but before

Install the current project as an example (in the build file: / home / paul / lucid / example /)

there is a pause of 15 seconds.

How can I find the reason for the slow start?

Answer 1

Try creating project/debug.sbt :

 logLevel := Level.Debug 

and look what you find. This is often a compilation of assembly files if you have project/*.scala .